The Role of Ultrasound in
Population-Based Breast Cancer Screening Programs
Edward Azavedo
156
Breast cancer is the most common malignancy that can affect a woman during her lifetime. In Sweden, breast cancer accounts for 26% of all the malignancies that affect women in our country. Even though we have made tremendous progress with both surgical and nonsurgical therapies, it is well documented that early detection is the best way to handle this disease. It is only through early detection that we can change the natural course of this disease with benefits both to individuals and to the entire society.
The first report regarding the beneficial use of early detection to fight this disease came from the HIP study in New York, wherein women who were offered mammog- raphy had a statistically significant lower mortality in breast cancer as compared to women who were not offered mammography. The other major report that revolu- tionized early detection was from the two-county study from Sweden published by Tabar et al. [1]. After that report many countries implemented nationwide screening programs to detect breast cancers at an early stage. The age groups that are screened vary within and among countries and are in a wide range, between 40 years at the lower level and 74 years at the upper level. Even the interval for screening varies a bit, but around 2 years is the generally accepted time interval for a screening program.
The main tool for early mass detection of breast cancers is mammography. When something abnormal or questionable is seen on a mammogram or when a woman reports breast symptoms, these women are recalled for further analysis.
The population-based breast cancer screening program in Sweden invites every single woman within the ages of 40 to 74 years, in certain cases 50 to 69 years, to have a mammogram every 2 years. In Stockholm we offer mammography screening for women aged between 50 and 69 years of age every 2 years. The first time a woman attends a screening examination, she always gets a two-view mammogram, that is, a MLO (mediolateral-oblique) and a CC (craniocaudal) view. If and when we see some- thing abnormal or questionable or if a woman reports actionable symptoms, then these women are recalled for further workups. At this stage, these women undergo a physical examination and get all the necessary extra views that include spot com- pressions, magnifications, and rolled views. During the past two decades, ultrasound
Faculty of Medicine, Karolinska Institute, Solna, 17176 Stockholm, Sweden
(US) examinations have been on the increase all over the world. Although US has been performed on breasts for a long time, its general use has increased exponentially with screening programs.
It is a well-known fact that the sensitivity of US to detect malignancies in dense breasts is higher as compared to mammography. This is one of the main reasons, in addition to the technological possibilities to study tumor details and multifocality, etc., that has made US so popular. Once the technology was mainly used to differen- tiate a solid from a cystic lesion, but that was long ago. The technological advance- ment in US is amazing, and we have today the possibility of seeing calcifications that are detected on mammograms and also the possibility of studying intraductal areas.
When we started our screening program, it was believed through the reported litera- ture that postmenopausal women have radiolucent breasts that are easy to analyze on mammograms. Our experience today reveals that the breasts, at least in Stockholm, do not show such a big difference between pre- and postmenopausal women. To add to that, we have today increasing use of hormone replacement therapy (HRT), which in many cases leads to increase in breast density. US helps us to rule out abnormali- ties in dense breasts with a higher degree of confidence.
Once a tumor is detected on a mammogram, it can be biopsied with either fine- needle aspiration (FNA) and/or a core biopsy to get a morphological preoperative diagnosis. These procedures can in many cases be done more easily and in a shorter time if the lesions detected on mammograms are visible on US, which they often are.
US can also help us to see the extent of the disease and study the margins toward the surrounding tissue. An US examination is often followed by the patient on our mon- itors, and when we see no abnormality or when we empty a cyst, the patients feel more relaxed than if they only had heard the result without visualizing such an event.
During the past few years, the use of HRT is on the increase, not only because of climacteric subjective reasons but also because of reports of the beneficial effects of HRT on osteoporosis, cardiovascular diseases, etc. As the age groups that attend a breast cancer screening program are usually around the peri- and postmenopausal ages, we have in many a case seen adverse effects of HRT on breast density. A mam- mogram may change from N1 (Wolfe’s classification of breast densities) to P2 and Dy patterns, making it a challenge to read these mammograms. In these situations the additional use of US increases our confidence to give the concerned women a trust- worthy report.
Another development on the therapeutic side is preoperative chemotherapy in advanced disease. In this cases an US examination can be of help in two different ways:
one is to monitor the effect of therapy and the other is to localize the tumor precisely with either a metal clip or charcoal. This will help the pathologists to identify the area to be examined microscopically in case the preoperative therapy shows a good response.
Today we have US as an integrated part of a breast cancer screening program start- ing from the recalled women. The first screening examination in population-based screening programs where the turnover is very high is mammography. A normal screening unit in countries that perform mammography screening for the whole pop- ulation can have up to 180 women per day, a number too high for performing US exams. Neither personnel nor time resources allow the use of US as the primary tool, but US has its given place in case of any doubt, may it be significant or not.
US in Population-Based Breast Cancer Screening 157
To conclude, I can state that we have gradually increased the number of US exams and US-guided interventions in our screening programs.
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