LITHUANIAN UNIVERSITY OF HEALTH SCIENCES

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LITHUANIAN UNIVERSITY OF HEALTH SCIENCES

Department of Endocrinology

Yizhaq Lan

Clinicopathological factors predicting outcomes of papillary thyroid

carcinoma:

Systematic Review

Master’s Thesis

Thesis Supervisor

Prof. Birutė žilaitienė MD, PhD

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1. SUMMARY

Author: Yizhaq Lan.

Title: Clinicopathological factors predicting outcomes of papillary thyroid carcinoma, a systematic review Interdiction: Papillary thyroid carcinoma (PTC) is the most common type of endocrine malignancy and

the most common type of thyroid malignancy accounting for 85% of all thyroid malignancies (1) (2). PTC usually harbors a favorable prognosis with 10-years survival rate of more than 90% of cases (3) (4). There are many studies showing variable value of different clinicopathological features of PTC and their

prognosis ability. In this study we reviewed, discussed and showed the power of each clinicopathological feature separately.

Research Aim: To review the current literature of the prognostic value of clinicopathological features of

papillary thyroid carcinoma.

Objectives: 1. Review the relationship between clinicopathological features and PTC prognosis. 2. Provide an insight for future diagnostic and prognostic aids of PTC.

Methodology: A systematic review was conducted through PubMed electronic database search. 36 most

relevant articles were included based on inclusion criteria of last 10 years, English language and human trials.

Results: This study reviewed and evaluate the value and correlation of the most common 8

clinicopathological factors of PTC and their association with histological variants and prognosis of the disease. This study showed strong correlation between older age, primary tumor size, extrathyroidal extension (ETE), lymph node metastasis (LNM), distant metastasis and BRAFV600E mutation and poor prognosis of PTC, while gender has shown to be less valuable clinically. This study also reviewed new aids for future use in the work-up of PTC.

Conclusions: Our conclusion was that although many factors are used clinically to help predict the

prognosis of PTC, some of these factors are able to “stand out” of the others in their value relative to other clinicopathological factors. Our conclusion regarding the importance of the clinicopathological factors reviewed in this study named according their value from the most to the least valuable is as follow: Distant metastasis > LNM > mutation > ETE > size = age. This study was also pointing two new diagnostic aids, Contrast-enhanced ultrasound (US) and thyroid stimulating hormone receptor (TSHR) mRNA which can be implicated in the diagnosis, prognosis and work-up of PTC.

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1. SANTRAUKA

Autorius: Yizhaq Lan.

Pavadinimas: Klinikopatologiniai veiksniai prognozuojant papilinės skydliaukės karcinomos baigtis,

Sisteminė apžvalga

Įžanga: Papilinė skydliaukės karcinoma (PSK) yra dažniausias endokroninės sitemos piktybinis navikas ir

dažniausias skydliaukės navikas, sudarantis 85% visų skydliaukės piktybinių navikų (1) (2). PSK pasižymi gera prognoze – 10 metų išgyvenamumas nustatomas 90% ligos atvejų (3) (4). Daugybė tyrimų rodo kintamas skirtingų klinikopatologinių PSK požymių reikšmes ir jų prognozavimo galimybes. Šiame tyrime mes apžvelgėme, aptarėme ir aprašėme skirtingų klinikopatologinių požymių svarumą atskirai.

Tyrimo tikslas: Apžvelgti dabartinę literatūrą papilinės skydliaukės karcinomos klinikopatologinių

požymių prognozinės reikšmės tema.

Uždaviniai: 1. Įvertinti ryšį tarp klinikopatologinių požymių ir PSK prognozės.

2. Pateikti įžvalgų apie būsimas PSK diagnostines ir prognozines priemones.

Tyrimo metodika: Sisteminė apžvalga buvo atlikta per PubMed duomenų bazę. Pagal tai, ar straipsnis

anglų kalba, išleistas per pastaruosius 10 metų bei jame aprašytas klinikinis tyrimas atliktas su žmonėmis, buvo atrinkti 36 aktualiausi straipsniai.

Rezultatai: Šis tyrimas apžvelgė ir įvertino 8 dažniausių klinikopatologinių PSK požymių reikšmę ir

koreliaciją su histologiniais variantais ir ligos prognoze. Tyrimu nustatyta stipri koreliacija tarp vyresnio amžiaus, pirminio naviko dydžio, užskydliaukinio išplitimo (ETE), metastazių limfmazgiuose (LNM), tolimųjų metastazių bei BRAFV600E_{mutacijų ir blogos PSK prognozės, tuo tarpu lytis turėjo mažesnę}

klinikinę reikšmę. Šis tyrimas taip pat apžvelgė naujas priemones būsimam PSK diagnozavimui ateityje.

Išvados: Priėjome išvada, jog iš daugelio veiksnių, naudojamų klinikinėje praktikoje PSK diagnostikoje,

kai kurie gali “išsiskirti” iš kitų savo reikšme sąsajoje su kitais klinikopatologiniais veiksniais. Atsižvelgiant į klinikopatologinių veiksnių svarbą, juos galima išskirti nuo didžiausios vertės turintį iki mažiausią vertę turinčio: Tolimosios metastazės > LNM (metastazės limfmazgiuose)> mutacija > ETE (išplitimas už skydliaukės) > dydis = amžius. Šiame tyrime taip pat aptartos dvi naujos diagnostinės priemonės- kontrastu sustiprintas ultragarsas (UG) ir skydliaukę stimuliuojančių hormonų receptorių (TSHR) iRNR- gali būti panaudoti PSK diagnozavimui, prognozavimui ir diagnostikai.

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2. CONFLICT OF INTEREST

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3. CLEARANCE ISSUED BY THE ETHICS COMMITTEE

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4. ABBREVIATIONS

AJCC- American Joint Committee on Cancer CCP- Columnar cell variant

cPTC- Classical papillary thyroid carcinoma ETE- Extrathyroidal extension

FNA- Fine needle aspiration GFR- Growth factor receptor

HCG- Human chorionic gonadotropin LNR- Lymph node ratio

mRNA- Messenger RNA

PRISMA- Preferred reporting items for systematic reviews and meta-analysis PTC- Papillary thyroid carcinoma

RET- Receptor tyrosine kinase

sPTMC- Solitary nodule papillary thyroid microcarcinoma SVPTC- Solid variant papillary thyroid carcinoma

TCV- Tall cell variant

TgAb- thyroglobulin antibody TSH- Thyroid stimulating hormone

TSHR- Thyroid stimulating hormone receptor US- Ultrasound

VEGF- Vascular endothelial growth factor

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5. TERMS

BRAF- refers to proto-oncogene located on chromosome 7. It encodes a protein which takes part in the

MAPK signaling pathway and play a role in cell growth and proliferation

I131 _{– Iodine- 131 is radioactive and toxic substance taken up by the thyroid gland, used for the treatment} of thyroid tumor

MAPK pathway- intracellular signaling pathway composed of many proteins which upon activation

leads to gene translation and proliferation taking part in cell growth and proliferation.

Thyroidectomy- a surgical operation aim to remove the thyroid gland partially or completely TNM stage- classification of tumors according size, lymph node and metastasis

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6. INTRODUCTION

Papillary thyroid carcinoma (PTC) is the most common type of endocrine malignancy and the most common type of thyroid malignancy accounting for 85% of all thyroid malignancies(1) (2), although being the most common type of endocrine malignancy its part in the general cancer incidence is relatively small accounting for only 1.5% of total cancer incidence. PTC usually harbors a favorable prognosis with 10-years survival rate of more than 90% of cases (3) (4). However, some studies have been presented 8-23% recurrence after treatment (5) (6). There are 4 major subtypes of thyroid carcinoma: 1. Papillary (80%) 2. Follicular (5-15%) 3. Anaplastic (5%) 4. Medullary (5%). Most carcinomas are derived from the follicular epithelium of the gland and the vast majority are well differentiated lesions.

The pathogenesis of all thyroid carcinomas are strongly associated with genetic factors, the most common genetic factor is alternation in the growth factor receptor (GFR) pathway. PTC is strongly associated with gain of function mutation of the receptor tyrosine kinase (RET) and BRAF (part of the MAPK pathway). RET gene located on chromosome 10q11, the gene it codes usually not expressed by thyroid follicular cells, this mutation is present in about 20-40% of PTC. RET mutation is found to be markedly elevated in patients who had prior radioactive exposure. BRAF mutation is the most associated gene alternation in PTC responsible for 30-50% of all PTC. BRAF mutation is a gain of function mutation which is a Valine to Glutamate substitution in position 600 (BRAFV600E), the mutation found to be associated with more aggressive form of PTC characteristics like metastatic disease, extra thyroid extension (ETE), high rate of recurrence and higher mortality rate. The presence of BRAF mutation in PTC tissue is one of the markers of possible malignancy. But data on BRAF mutation prognostic value is still contradictory and majority of the available PTC clinical guidelines use clinicopathological features of PTC to predict aggressiveness of the cancer. PTC is not only affected by genetic factors, the environmental factors such as ionizing radiation exposure in the first 2 decades of life is also strongly associated with the disease.

PTC occur throughout life mostly between 25-50 years of age. Most common risk factor is exposure to prior radiation. The course of disease is mostly asymptomatic, but may appear with hoarseness, dysphagia, cough and dyspnea in more advanced forms of the disease. There is one main test to diagnose PTC which is fine needle aspiration (FNA). The development in cytology accuracy made FNA the preferred method to use for diagnosis.

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Many studies have been done trying to link different clinicopathological features and histological variants to the prognosis of PTC. Factors like age, gender, extra thyroidal extension, LNM, distant metastasis, multifocality and genetic mutation have been shown to effect prognosis differently. In this study we are going to systematically review the most recent studies that showed correlation between different clinicopathological features, evaluate their prognostic value and give a future insight to a new prognostic and diagnostic factors for PTC which can be implicated in future medicine in order to improve effectiveness of diagnosis, treatment and follow up.

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7. AIM AND OBJECTIVES

Research Aim:

To review the current literature of the prognostic value of clinicopathological features of papillary thyroid carcinoma.

Objectives:

1. Review the relationship between clinicopathological features and PTC prognosis. 2. Provide an insight for future diagnostic and prognostic aids of PTC.

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8. RESEARCH METHODOLOGY AND METHODS

Search strategy:

This systematic review was conducted following the PRISMA (preferred reporting items for systematic reviews and meta-analysis) statement (7). Total of 66 literature sources were reviewed. Literature was selected through a search of PubMed electronic database. The most 36 relevant (by abstracts and full text review) articles were selected. The search was restricted to English and last 10 years articles only (with an exception of 2 articles from 2002, studying the Chernobyl nuclear reactor meltdown influence on PTC) .

Types of publication and studies:

This review included systematic reviews and clinical trials published in English during the last 10 years.

Information source:

The information source was MEDLINE-PubMed electronic database.

Selection criteria:

The search terms and keywords used include:

- “Papillary thyroid carcinoma/cancer and clinicopathological factors/features” - “Papillary thyroid carcinoma/cancer prognostic factors”

- “Papillary thyroid carcinoma/cancer and/or age and/or gender and/or size and/or lymph node and/or metastasis and/or genetic mutations and/or histological/pathological variants.”

The search was restricted to English language, last 10 years publications and human trails.

Exclusion criteria:

- More than 10 years publication (except of 2 studies from 2002). - Less relevant articles (by abstract review).

-trials done not on human

Data collection process:

The search results provided 673 articles. After reduction for not more than 10 years, human trials and English language 373 articles left. Out of this 66 articles left based on title exclusion and exclusion for

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duplication. Finally 36 articles were selected based on abstract and full text review. Figure 1. Show Flow chart for articles exclusion and inclusion processes in the study.

Figure 1. Flow chart for articles exclusion and inclusion processes in the study

673 Articles identified using the keyword electronic database search

373 potentially relevant articles

300 articles were excluded after reduction for last 10 years, human trails and English language

307 Articles excluded based on title review and duplication

66 Abstract reviewed

30 Articles excluded based on abstract and full text review

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9. RESULTS AND THEIR CONCLUSIONS

9.1 Age and its effect on PTC prognosis

Table 1. Age and its effect on recurrence of PTC

Reference Recurrence/Number of patients<45 age Recurrence/Number of patients>45 age Statistically significant correlated with poor prognosis (p-value<0.05) yes/not Raymon H. Grogan 2013 57/196 (29%) 42/73 (57.5%) Yes

Hye Jeong Kim 2013

72/990 (7.2%) 66/1105 (5.9%) No

In Sun Ryu 2014

9/137 (6.5%) 12/146 (8.2%) No

Age is a very important prognostic feature of PTC, especially for cancer related death. Age as a clinicopathological factor for the prediction of PTC poor prognosis is an example of a factor which has been widely investigated in many studies. The UICC/AJCC (American Joint Committee on Cancer) TNM staging system (8) implicated age as a risk factor and divides PTC age risk between patients younger or older than 45 years of age. Table-1 summarize the researches reviewed in this study and showing age and its correlation with PTC prognosis.

In a study done by Grogan et-al (9) evaluated the risk factors of 269 patient for the prognosis of PTC. Out of all the risk factors that have been investigated age was found to be the only patient characteristic associated with increased risk of recurrence using univariate analysis. They suggested to divide age group differently according 3 age groups model: <45, 45-60 and >60, they found that group aged<45 had the best prognosis while age group 45-60 had the greatest disease related mortality and group aged >60 mostly died from other reason than PTC. In another study was done by Ito at-al. (2) 5897 patient with PTC checked for their risk factors association with overall survival and cause-specific survival. The most important prognostic value for overall survival was patient age (>55 years), even more then distant metastasis (M1) indicate an indolent course of disease. In contrast other studies did not find age to be a statistically

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significant factor in the prognosis of PTC. For instance in a study was done by Kim et-al. (10) and investigate multifocality of PTC As a poor prognostic characteristic and what clinicopathological features influence it, the study reported that age was not found to be statistically significant related to a poor disease outcomes. In another study done by Ryu et-al. (11) lymph node ratio was investigated as a predictive clinicopathological factor. In this study age (>45 years) was not found to be statistically significant correlated with disease survival or recurrence rate although the author reported that age was not found to be correlated potentially due to relatively young age of the study cohort. In a study was done by Eranga et-al (12) thyroglobulin antibody (TgAb) blood level after initiet-al surgery were checked as a clinicopathologicet-al factor for the predication of PTC prognosis and where compared to other clinicopathological factors, Although age was found to be a factor associated with poor prognosis, when TgAb was focused, age was not found to be correlated with PTC prognosis. In a meta-analysis was done by Guo et-al (13) a total of 13 studies (2008-2014) with 7048 PTC patients were investigated in order to point out what clinicopathological factors are correlated with poor disease prognosis, in this study age (>45 years) was not found to be statistically significate associated with PTC prognosis. However, when stratified the participants by location, Asian countries (China, Korea, and Japan) and Western countries (America, France, Italy and Australia) a statistically significant correlation for age was found in Western countries but none in Asian.

9.2. Gender and its effect on PTC prognosis

Table 2. Gender and its effect on the recurrence of PTC

Reference Recurrence/Male Recurrence/Female Statistically significant correlated with poor

prognosis (p-value<0.05) yes/not Raymon H. Grogan 2013 39/89 (43.8%) 60/180 (33.3%) Not

Hye Jeong Kim 2013 28/275 (10%) 110/1820 (6%) Yes Schelto kruijff 2014 33/246 (13.4%) 61/937 (6.5%) Yes In Sun Ryu 2014 6/60 (10%) 15/223 (6.7%) Not Wei Zhang 2016 21/80 (26%) 44/456 (9.6%) Yes

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Gender disbalance in cancers incidence, aggressiveness, recurrence and mortality have been shown in many cancer types. For example, in gender- specific organ such as prostate, ovary, breast and uterus the disbalance can be explained easily. However, in some other shared organs like liver, lung and thyroid, the difference in incidence and prognosis is well established and yet more difficult to be explained (14).

Thyroid cancer incidence is one of the fastest to grow worldwide. It is almost 3 times more common in females then in males, makes it the 7th most common cancer among female, but it is not even among the 15th most common cancers in males (14). The gender disbalance in thyroid cancer is also well correlated with specific histological subtypes of the tumor. The more aggressive subtypes of thyroid cancer which also harbor a poorer prognosis are undifferentiated/anaplastic thyroid cancer and medullary thyroid cancer showed equal incidence in both genders. However, the more differentiated thyroid cancer which are less aggressive and showed to be associated with a better prognosis, follicular thyroid carcinoma and PTC, are much more common in females. Moreover, in most of the studies male gender has shown to be significantly more associated with poorer prognosis, higher recurrence, lower disease-free survival and higher mortality.

Table-2 summarize the researches reviewed in this study and showing gender and its correlation with PTC prognosis. In a study done by Grogan et-al. (9) male gender was not found to be associated with higher recurrence or increased mortality. In a study done by Kim et-al. (10) male gender was found to be statistically significant related to PTC multifocality and increased risk for recurrence and mortality. In a study done by Kruigiff et al. (15) male gender was found to be associate with higher recurrence and increase incidence of reoperative surgery. In a study done Ryu et al. (11) male gender was not found to be associated with higher recurrence or mortality when PN1a (lymph node metastasis in paratracheal, prelaryngeal, or upper mediastinal). In a study done by zhand et-al. (16) male gender was found to be associated with both higher recurrence and mortality.

It has been hypothesized that environmental, dietary, reproductive and menstrual factors may contribute to the gender disbalance. Radiation exposure from external beam and ionized radiation especially in young age has been well shown to be associated with PTC. Studies that have been investigating the atomic bomb events in Japan and Chernobyl reactor meltdown showed that almost all radiation- associated thyroid cancers were PTC and the greatest risk was for children (17). A meta-analysis of 7 studies showed that female had almost 2 times increased incidence of thyroid cancer. However, no individual study was

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able to show a statistical significant correlation between the genders. Sex hormones influence on PTC has been hypothesized to be a cause of the gender difference. However, many studies checking the influence of age of menarche, menopause and number of pregnancies showed inconclusive results. Some female hormones such as HCG (human chorionic gonadotropin) are known to be molecularly similar to thyroid stimulating hormone (TSH) and caused rapid growth of thyroid tumors (benign and malignant) (14). Moreover, estrogen showed to increase the growth of thyroid nodules but has not shown to effect malignant nodule (18). In another study that was done by Jonklas et el (19) gender disbalance was found only before the age 55 years, with women having better prognosis than men when diagnosed at younger age. The study also found no difference in prognosis between the genders when the disease was diagnosed at older age. The study suggested that women have better prognosis because they tend to be diagnosed at younger age due to fluctuating size of benign thyroid nodule. When they adjusted the study for age and stage of the disease, no difference between the genders was found. In a pool analysis done by Kai et al. (13) 13 studies (2005-2014) with a total of 7048 PTC patients have shown statistically significant association between male gender and higher incidence of recurrence and mortality rate among PTC patients.

9.3 Lymph node metastasis and its effect on PTC prognosis

PTC main way of spreading is through lymph node metastasis. The mechanism by which PTC spreads to lymph node is not well understood. However recent studies suggests that the tumor secrets cytokines such as vascular endothelial growth factor C and D (VEGF C/D) which binds VEGF receptors on the endothelium of lymph node and cause proliferation of capillaries and lymph nodule tissue. The diagnosis of lymph node metastasis is done by several tests such as FNA and cytology, ultrasonography, scintigraphy and positron emission tomography. Many studies pointed out some important factors that can predict lymph node metastasis such as male gender, absence of primary tumor capsule, tumor size of more than 2cm, older age and ETE are among the major factors contributing to increase risk of lymph node metastasis in PTC. Recurrence of PTC in lymph node after the initial surgery has been associated with adverse survival rate especially in patients older than 45 years of age. Current guidelines of the AJCC TNM staging system (8) for PTC suggests affected lymph node and their location should be accounted for only older patients (more than 45 years old) and the staging predict only higher mortality rate but not recurrence. Lymph node metastasis in PTC paints has been proven in many studies to be correlated with higher rate of recurrence and mortality (9) (10) (16).

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In a meta-analysis done by kai et-al (13) and evaluated the clinicopathological factors of a total of 7049 patient with PTC concluded sharply that lymph node metastasis is statistically significate associated with higher recurrence and mortality rate. In another study done by Ryu et-al (11) and checked whether lymph node ratio of central compartment can predict the likelihood of recurrence in PTC, they found that in younger age (less than 45 years old) lymph node ratio is statistically significant associated with recurrence rate and suggest to monitor more closely patient who have more than 3 lymph node involved and a ratio of more than 0.65.

9.4 Primary tumor size and its effect on PTC prognosis

Table 3. Size and its effect on the recurrence of PTC

Reference >2cm/Recurrenace >2cm/Recurrenace Statistically significant correlated with poor

prognosis (p-value<0.05) yes/not Raymon H. Grogan 2013 43/94 (45.7%) 22/128 (17%) Yes Schelto kruijff 2014 69/578 (12%) 18/615 (2.9%) Yes In Sun Ryu 2014 8/66 (12%) 8/217 (3.6%) Yes Wei Zhang 2016 71/382 (18.5%) 8/151 (5.2%) Yes

Larger primary tumor size in PTC has been shown and proven to be correlated with poor prognosis of PTC in many studies. Table-3 summarize the researches reviewed in this study and showing size and its correlation with PTC prognosis. In a study done by Grogan et-al (9) which tried to estimate what risk factors of PTC are most associated with poor prognosis under prolonged follow up, primary tumor size of more than 2 cm was associated with higher risk of recurrence but not with increase mortality. They were also been able to show that patient with tumor size of more than 1 cm may have benefit of reduced recurrence when radioactive iodine (RAI) treatment was added to their regime. In another study done by Kruijff et-al. (15) 1183 patients with PTC checked for their risk factors of postoperative recurrence, this study showed that primary tumor size of more than 2 cm was associated with postoperative lateral neck compartment reoccurrence and reoperation. In another study done by Ryu et-al (11) Lymph node ratio (LNR) was

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comperes to other clinicopathological risk factors in order to predict its value. In this study, out of most clinicopathological risk factors a univariate analysis showed that only large primary tumor size and LNR were associated with increased risk of recurrence. In another study done by Zhang et-al. (16) a tumor size of more than 2 cm was associated with increased risk of recurrence and it was concluded in this study that patient with a primary tumor size of more than 1 cm should undergo total thyroidectomy in order to decrease risk of recurrence.

9.5 Extrathyroidal extension and its effect on PTC prognosis

Table 4. Extrathyroidal extension and its effect on the recurrence of PTC

Reference Recurrence/ETE(+) Recurrence/ETE(-) Statistically significant correlated with poor

prognosis (p-value<0.05) yes/not Raymon H. Grogan 2013 28/34 (82.3%) 71/235 (30.2%) Yes

Hye Jeong Kim 2013 99/1260 (7.8%) 39/835 (4.6%) Yes Schelto kruijff 2014 58/387 (15%) 36/796 4.5%) Yes In Sun Ryu 2014 13/205 (6.3%) 4/78 (5.1%) Not Wei Zhang 2016 21/120 (17.5%) 44/416 (10.5%) Yes

Extrathyroidal extension (ETE) means invasion of the primary tumor into adjacent tissues. ETE has been studied widely and it has been considered as an important clinicopathological factor which can predict prognosis of PTC. The AJCC staging system (8) of PTC considers T3 if the primary tumor size is bigger than 4cm. however AJCC considers any ETE as T3 regardless of the primary tumor size, teaching us the significance of ETE. The most common sites for PTC invasion are the perithyroid soft tissue, sternothyroid muscle, larynx, subcutaneous tissue, trachea, recurrent laryngeal nerve and esophagus.

The diagnosis of ETE can be performed before or after the surgery. The establishment of ETE requires in most of the cases additional treatment with RAI. Table-4 summarize the researches reviewed in

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this study and showing ETE and its correlation with PTC prognosis. In a study done by Park et-al (20) which checked the significance of non/micro/macro ETE on the outcomes of PTC concluded that the degree of ETE is correlated with the Prognosis of PTC, in which micro ETE was associated with lower 5-year reoccurrence free survival than non ETE. However macro ETE was associated with lower 5-year recurrence free survival than micro ETE. In a study done by Grogan et-al. (9) and checked the impact of clinicopathological factors in PTC prognosis over long term period of follow up concluded that ETE is associated with increased risk of recurrence. However they were not able to show correlation between ETE and increased risk of death. In another study done by Kim et-al (10) and checked the value of multifocality and bilaterality on PTC prognosis, they found that ETE was statistically significant associated with multifocality which was correlated with increased risk of recurrence and death compere to solitary primary tumor. In another study done by Kruijff et-al (15) and checked the pattern of recurrence in PTC found that ETE was statistically significant associated with higher rate of recurrence as well. However in another study done by Ryu et-al (11) found no statistical significant correlation between ETE and recurrence of PTC. In a recent study done by Zhang et-al (16) checked 2 sites of extension, to muscle/fat tissue and adjacent organ. In both cases the extension was associated with increased risk of recurrence. Moreover they suggested more extensive surgery for those with ETE, prolonged and closer monitoring and follow up after the operation.

9.6 Distant metastasis and its effect on PTC prognosis

Distant metastasis of PTC is by far the most important clinicopathological risk factor which is predictable of poor prognosis in PTC. PTC mainly spreads through the lymphatic tissue which makes lymph metastasis and regional metastasis the most common sites for metastasis. Distant metastasis spread rate in PTC is relatively small accounting for only about 1% of cases. There are 2 main sites for metastasis in PTC which are the lungs and bones, other less common sites of PTC metastasis include the brain, skin, liver, kidneys, pancreas, stomach, adrenal gland, big blood vessel, muscles and heart. The AJCC staging system (8) classifying PTC as stage IVc (the most advanced stage) for any metastasis (M1) regardless of the size (any T) and lymph node (any N) state. All the studies which were reviewed in this systematic review found distant metastasis as major clinicopathological factor which predicting poor prognosis in term of higher risk of recurrence and mortality rate. Some studies tried to characterize the significates of different sites and extent of PTC metastasis.

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In a study done by Kwong et-al (21) it was demonstrated that patient with distant active pulmonary metastasis may remain stable for long time on TSH suppression treatment without any other treatment. Nixon et-al (22) showed in their study that more than 50% of patient with well differentiated thyroid tumor who have distant metastasis die within 5 years despite surgery and RAI therapy, they also concluded that extra-pulmonary metastasis harbor a poorer prognosis than pulmonary metastasis in PTC. However in another study done by Farina et-al (23) and checked the significance of rare sites metastasis of PTC conclude that although rare sites of metastasis such as pancreas, liver skin etc. usually represents more aggressive disease and poor prognosis in some cases if they are localized, diagnosed early in the course of the disease and resected completely, they may have a better prognosis than those tumors with more common sites of metastasis such as lungs and bones. In their study they also suggested some different methods for early diagnosis such as persistent high level of thyroglobulin, because rare sites metastasis tend to be undiagnosed until late stage or misdiagnosed which may lead to poorer prognosis.

9.7 Genetic mutations and its effect on PTC prognosis

The vast majority of causative mutation in PTC are BRAFV600E_{, RET/PTC and RAS. Of these,} BRAFV600E_{is the most common mutation to be associated with PTC. The}_BRAFV600E_{mutation activates the}

MAPK signaling pathway leading to accelerated cell growth and proliferation.

In a study done by Zhen et-al. (24) BRAFV600E _{mutation found to be associated with poor prognosis}

even in patient with solitary nodule papillary thyroid microcarcinoma (sPTMC) which is usually less aggressive compere to PTC, They also suggested more aggressive treatment and longer period of follow up for those diagnosed with BRAFV600E_{sPTMC. In another study done by Liu et-al. (25)}_BRAFV600E _mutation

was found to be associated with tall cell variant (TCV) PTC which is the most aggressive variant of PTC. In another study done by Choi et-al. (26) found that BRAFV600E _{mutation is associated with SUVmax on}

preoperative PET/CT scan in PTC. In contrast a study done by Geng et-al (27) checked the significance of

BRAFV600E _{mutation in pediatric PTC found that the}_BRAFV600E _{mutation was associated with earlier diagnosis}

of PTC and better outcomes. Vuong et-al. (28) investigated the significant of BRAFV600E _{and telomerase}

reverse transcriptase (TERT) mutations on PTC prognosis, they found that aggressiveness of PTC can be classified according 3 subtypes of genetic mutation combination written from the most to the least

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aggressive: BRAFV600E_{+ TRET>> TRET only=}_BRAFV600E _{only>> non mutation. In a meta-analysis done by}

Liu at-al. (29) a total of 20764 patient with PTC were checked for their BRAFV600E _mutation,

In their study BRAFV600E _{mutation was found to be associated with ETE, LNM, higher TNM stage, higher}

recurrence and mortality. However there was no statistical significance correlation between BRAFV600E

mutation and distant metastasis which is the most important clinicopathological feature of PTC.

9.8 Histological variants and its effect on PTC prognosis

Pathological and histological evaluation of PTC plays a major role in the diagnosis, work-up and prognosis of the disease. PTC derived from follicular epithelial cells. There are many histological variants of PTC such as classical, cystic, follicular, solid, cribrifom-morular, oncocytic, diffuse sclerosing, tall cell, columnar cell, some of which have prognostic implications (e.g. tall cell and columnar cell variants are considered to have a worse prognosis, while the classical has good prognosis) (30) .

The international guidelines does not fully support the existence of TCV to be a major risk factor. TCV histology is classified as a low-risk factor according to the European Thyroid Association guidelines (31) and as an intermediate risk factor according to the American Thyroid Association guidelines (32).

In a recent study done by Gunlap et-al. (33) and evaluate the prognostic value of TCV compere to classical variant PTC (cPTC) which considered to have good prognosis (30) (31) (32). Their results showed that in all stages, the incidence of ETE, lympho-vascular invasion and lymph node metastasis was statistically significant higher in TCV compered to cPTC. They also found that in all stages recurrence and recurrence with distant metastasis was significantly higher in TCV. They conclude that TCV is an independent poor prognostic factor, even when it was diagnosed at early age. Patients with TCV required more aggressive therapy and closer follow-up. In a recent meta-analysis done by Liu et-al. (25) the clinicopathological factors of TCV were compered cPTC. Their results showed that Patients with TCV were statistically significant more associated with higher TNM stage, multifocality, extrathyroidal extension, vascular invasion, distant metastasis, lymph node metastasis, BRAF mutation, lower disease-specific survival, and overall survival.

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Columnar cell variant (CCV) PTC is another histological type associated with poor prognosis, yet not as common as TCV. In study done by Jiang et-al. (34), CCV was compered to encapsulated variant PTC, which is associated with good prognosis. Their results showed that CCV tumors tended to be larger And appeared in older males (>65 years age). Moreover CCV was associated with higher rates of ETE, multifocality, lymph node and distant metastases. In terms of recurrence and survival, CCV was found to be associated with both, higher recurrence rate and poor survival. In another study done by Baloch et-al. (35) and compered the most aggressive histological variants of PTC highlighted 2 histological subtypes of PTC. The most common aggressive variant of PTC is TCV, the aggressiveness was ascribed to clinicopathological features and the histological subtype and CCV although not as common as TCV, was also found to be associated with poor prognosis particularly in symptomatic older patients, with larger tumors. In meta-analysis study done by Vuong et-al. (36) and investigate the prognostic value of a rare, solid variant PTC (SVPTC). In their work 11 studies were analyzed and compered the significance of SVPTC with cPTC. They found that SVPTC showed a significantly higher risk for vascular invasion, recurrence and mortality compared to cPTC. They also mentioned a unique genetic profile associated with SVPTC. BRAF mutations incidence was lower in SVPTC compare with cPTC. On the other hand, gene fusion RET/PTC or NTRK1/3, were more prevalent in SVPTC.

9.9 Future insight into clinicopathological features of PTC researches

PTC is the most common endocrine cancer. LNM occurs in 30-40% of cases, and microscopic LNM may occur in 80-90% (37). As discussed earlier in this study, LNM is an important clinicopathological risk factor which can predict the prognosis of PTC. Regional metastasis to lymph node could be considered as the second most valuable predictor of PTC after distant metastasis. Identifying regional lymph node and characterized them is an important clinical practice which can aid in personalizing treatment and work-up of patients.

Recent studies have been focused on how to screen high risk patients, FNA is the gold standard in the diagnosis work-up of patients with PTC. Current guidelines basically suggests doctors to aspirate any nodule seems suspicious during US examination (32). US is used extensively in the diagnosis and preoperative staging of PTC to determine the extent of operation. Yet LNM and especially microscopic LNM may not appear abnormally on US examination. In a recent research done by Liu Y. et-al (38) in 2017

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checked the value of contrast-enhanced US examination of LNM based on the findings of another research (39), found that LNM has more extensive blood flow which is a direct correlation with the ability of the tumor to secrets VEGF. In their study they were able to show for the first time that patients with LNM and microscopic LNM has earlier and faster enhancement on contrast-enhanced US. They suggested this method as a screening tool to determine which lymph node should be aspirated for more effective diagnostic and treatment of PTC.

In study done in 2017 by Liu R. at-al (40) a new blood marker has been investigated for its value in early Non-invasive diagnosis, prognosis and follow-up of PTC. In this study peripheral blood thyroid stimulating hormone receptor (TSHR) mRNA levels were measured pre and postoperatively and compered to normal thyroid and other thyroid-associated diseases patients. It was found that in PTC patients peripheral blood of TSHR mRNA levels were elevated and associated significantly with other clinicopathological factors such as older age, capsular invasion, LNM, BRAFV600E mutation and distant metastasis. It was also found that TSHR mRNA elevated levels were correlated with higher recurrence of PTC. Their findings suggested that TSHR mRNA level in peripheral blood promising a novel biomarker for non-invasive, early detection, diagnosis, treatment and follow-up of PTC. In a study done in 2017 by Yang et-al. (41) a gene expression of PTC was investigated and found that PTC under-express autophagy-associated gene, Becilin-1 and microtubule-associated protein-Becilin-1 light chain 3 (LC3). Their research conclude that compared with healthy thyroid gland tissue, Beclin-1 and LC3 were under-expressed in PTC patient regardless of patient’s age, tumor size and gender, especially in patient with metastatic tumor. In a study done in 2017 by Liang et-al. (42) checked the tyrosine kinase-like orphan receptor-2 and its ligand Wnt 5a, pro-tumorigenic role in PTC. In this study the expression of orphan receptor 2 and its ligand Wnt 5a were found to be significantly elevated in PTC patients and were correlated with tumor stage and LNM. Moreover it was suggested that orphan receptor-2 can be a future target of treatment of PTC.

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10. CONCLUSIONS

In this study 8 different most important clinicopathological risk factors of PTC were reviewed and discussed separately for their clinical value in the prediction of PTC prognosis.

• Age- although older age has been shown in some studies not to be significantly associated with adverse PTC prognosis. Yet most studies shows older age to be correlated with poor PTC prognosis. Moreover the UICC/AJCC TNM staging system (6) consider older age as a major risk factor.

• Gender- this study has shown that although PTC is much more common among female gender than male. Yet gender as a prognosis factor for PTC is a much less effective feature to relay on relative to other feature reviewed in this study. Too many studies showed contradicting results regarding the significance of gender as a predictive factor.

• LNM- The main way of PTC spreading is through lymph tissue and as such LNM is a well-known major risk factor for poor PTC prognosis with new methods focusing on better detection of LNM.

• Primary tumor size- This study showed consensus regarding Primary tumor size and prognosis of PTC with larger primary lesion being associated with more adverse outcomes.

• ETE- Is another well-known major risk factor has been shown in this study as well to be associated with poor PTC prognosis.

• Distant metastasis- This factor is by far the most important clinicopathological factor of PTC. All studies that have been investigating clinicopathological features of PTC as well as this study point out distant metastasis as the single most valuable clinicopathological factor for the prediction of PTC prognosis. • Genetic mutation- As in many other different malignancies genetics plays an important role in the

genesis and prognosis. This study showed the major genetic alternation, BRAFv600e to be associated with poor prognosis of PTC.

• Histological variants- careful pathological-histological examination of PTC plays a major rule in the diagnosis, work-up and prognosis of the disease. In this study the most common histological variants associated with poor prognosis of PTC were highlighted. TCV and CCV have been shown to be the most important clinically in terms of poor prognosis because they were not only common histological variants of PTC, but also associated with worse clinicopathological features, higher recurrence rate and poor survival rate.

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In this study we also gave an insight for new diagnostic and prognostic markers which can help in the work-up of PTC. There are many new studies which try to investigate new diagnostic and prognostic markers for PTC, out of all the studies which were reviewed in this article two were able to show outstanding results.

• Contrast enhanced US- This new method is based on the fact that PTC secrets VEGF and has increased blood supply which makes even small and very hard to diagnose nodule to be better visualized under US and help evaluate the extant of the disease better.

• TSHR mRNA- This study was able to find new blood marker which can be measured non-invasively and is correlated with the aggressiveness of the disease, this marker potentially can be used alongside other clinicopathological feature to better evaluate the extant and prognosis of the disease in individual patient.

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