Oncology—Urology
I. KIDNEY CANCER
Renal cell carcinoma (RCC) arises from the renal tubular epithelium and accounts for the majority of the adult kidney tumors. The tumor is highly angioinvasive and results in widespread hematogenous and lymphatic metas- tases especially to the lung, liver, lymph nodes, bone, and brain. Metastases are present in about 50% of patients at initial presentation. Radical nephrectomy is the main treatment for the early stages of disease, although palliative nephrec- tomy may also be performed in advanced disease with intractable bleeding.
Solitary metastasis may also be resected. RCC responds poorly to chemo- therapy. Radiation therapy for RCC is used for palliation of metastatic sites, specifically, bone and brain. Immunotherapy with biologic response modifiers such as interleukin-2 and interferon alpha has the most impact on the treat- ment of metastatic disease. The five-year survival may be as high as 80–90% for early stages of disease, while advanced disease carries a poor prognosis.
Current imaging tests, including CT, MRI, and skeletal scintigraphy, are not sufficiently accurate to detect recurrent and metastatic disease. Preliminary studies of PET imaging of RCC have revealed a promising role in the evaluation of indeterminate renal masses, in pre-operative staging and assessment of tumor burden, in detection of osseous and non-osseous metastases, in restaging after therapy, and in the determination of effect of imaging findings on clinical management. However, few other PET studies have demonstrated less enthusi- astic results and no advantage over standard imaging methods.
A relatively high false-negative rate of 23% has been reported with FDG PET in the preoperative staging of RCC when compared to histological analy- sis of surgical specimens. Other studies have reported high accuracy in charac- terizing indeterminate renal masses with a mean tumor-to-kidney uptake ratio of 3.0 for malignancy. The superiority of FDG PET in evaluating skeletal metas- tases as compared to bone scintigraphy has also been shown. These mixed observations are probably related to the heterogeneous expression of GLUT-1 in RCC, which may not correlate with the tumor grade or extent.
FDG PET can also alter clinical management in up to 40% of patients with suspicious locally recurrent and metastatic renal cancer (Fig. 1). In a recent study of the utility of FDG PET in re-staging RCC, a sensitivity of 87% was reported at a specificity of 100%. In another report, the diagnostic performance of FDG revealed a sensitivity of 71%, specificity of 75%, accuracy of 72%, neg- ative predictive value of 33%, and positive predictive value of 94%. Therefore, FDG PET appears to offer modest diagnostic accuracy in re-staging RCC. A negative study may not exclude disease, while a positive study is highly suspi- cious for malignancy. The diagnostic accuracy of FDG PET appears not to be improved by semi-quantitative analysis, which is probably due to the funda- mental variability of glucometabolism in RCC. Since FDG is excreted in the urine, the intense urine activity may confound lesion detection in and near the renal bed. Intravenous administration of furosemide (lasix) has been proposed to improve urine clearance from the renal collecting system, although the exact
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A
Figure 1: A 49-year-old male with metastatic right renal cell carcinoma. A: Chest and abdomen CT studies demonstrate multiple bilateral pulmonary lesions and a large necrotic right renal mass.
benefit of such intervention in improving lesion detection remains undefined.
Other PET tracers (e.g., C-11 acetate) may also suitable in the imaging evalua- tion of patients with suspected RCC.
II. BLADDER CANCER
Bladder cancer is the most frequent malignant tumor of the urinary tract and more common in patients aged 50 to 80. Typical presentation is hematuria.
Depth of tumor penetration into the bladder wall forms the basis for disease
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Figure 1: (Continued) B. Coronal PET shows intense hypermetabolism at the rim of the renal mass and in the pulmonary lesions.
staging and is the most important prognostic factor. Transitional cell carcino- ma is the most common histopathology but squamous cell and adenocarcino- ma may also occur (Fig. 2). Diagnostic procedures may include cystoscopy with biopsy, excretory urography or retrograde pyelogram, pelvis ultrasound and CT
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B
Figure 2: A 54-year-old male with invasive squamous cell carcinoma of the urethra.
A. MRI shows 3 × 2-cm penile mass originating from the bulbous portion of the urethra encroaching upon the corpora cavernosum and spongiosum, located 1 cm anterior to the external sphincter. B. PET shows a corresponding oval-shaped area of elevated tracer uptake in the urethra at midline.
of the chest, abdomen, and pelvis. Superficial lesions may be treated with endo- scopic resection, fulguration, or photodynamic therapy. Cystectomy with uri- nary diversion is indicated when the tumor is invasive. Radiotherapy may be employed as adjuvant therapy, in combination with other therapies, or as a palliative measure. There is no established systemic chemotherapeutic regimen for the treatment metastatic bladder carcinoma. The five-year survival is about 90% for superficial disease and about 60% for invasive disease. Systemic disease has a dismal prognosis.
FDG PET has been found to be modestly accurate in the diagnosis of blad- der cancer and in the detection of pelvic lymph node and distant metastases.
The intense excreted FDG activity in the urinary bladder is main hindrance in the evaluation of the organ and the adjacent pelvic structures, including the lymph nodes. Use of furosemide (lasix) and/or bladder lavage may help in reducing the urine activity but the exact utility of such intervention is not established. The primary bladder carcinoma and the lymph node metastases may exhibit an SUV in the range 1.7 to 6.2. For lymph node staging, a sensitiv- ity of 67% and a specificity of 86% have been reported. Other PET radiotracers including C-11 methionine and C-11 choline may also be potentially useful in the imaging evaluation of bladder carcinoma.
BIBLIOGRAPHY Kidney Cancer
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