In the United States, an estimated 12.8% of women will be diagnosed with breast cancer at some point in their lifetime. Although the diagnosis is daunting, survival odds are incredibly favorable if the cancer is detected early. In fact, the 5- year survival rate for localized cancer, defined as having no signs of cancer spreading to other tissues, is 99%.
Screening mammography uses low- dose x-rays to image breast tissues and the advent of mammograms allows the detection of small tumors. One study used data collected from 1975 to 2012 and the proportion of breast tumors that were deemed small (<2 cm) at detection was shown to increase from 36% to 68%. Conversely, the detection of large tumors (≥ 2cm) decreased from 64% of breast tumors to 32%. Early tumor detection improves treatment success and smaller tumor size at detection is associated with lower 10- year risk of death from breast cancer. Therefore, screening mammograms is believed to reduce breast cancer mortality. In fact, mammograms are estimated to reduce approximately 8-12 deaths per 100,000 and reduce breast cancer mortality up to 30%[2, 3]. The benefits of mammograms are many and, for women with average breast cancer risk, the American Cancer Society recommends women between the ages of 40 and 44 years to have the opportunity to begin annual screening. They also recommend annual screening for women between the ages 45 to 54 years and screening every 2 years for women older than 55 years .
Screening mammography is not without their limitations and one limitation is the commonality of false positive findings. Among women who started annual screening at age 40, the probability of having at least one false- positive after 10 years is 61.3%. The odds decrease to 41.6% in individuals with biennial screening. Following positive findings, most patients undergo additional imaging. A small percentage of women may undergo biopsy and the 10- year probability of patients undergoing a biopsy procedure after a false positive mammogram is 7.0% with annual screening and 4.8% with biennial screening . During a biopsy procedure, a small tissue or fluid is removed from the suspicious area and checked for the presence of breast cancer. The three types of biopsies in the order of least to most invasive are fine- needle aspiration, core- needle biopsy, and surgical biopsy. During fine- needle aspiration, the physician inserts a thin needle to the suspicious lump and collects a sample of cells or fluid. The procedure allows the physician to distinguish whether a suspicious lump is a fluid- filled cyst or a solid mass. Core-needle biopsy uses a larger “core” needle to remove a small tissue from the breast and is often performed under local anesthesia with the aid of imaging equipment (i.e. ultrasound). The most invasive form of biopsy is surgical biopsy in which a surgeon makes a one- to two- inch cut on the breast and remove a suspicious lump. Once the biopsy is completed, the tissue is examined for the presence of cancer and, if found positive, the biopsy report will guide decisions regarding treatment options.
False positive mammogram finding subjects individuals to unnecessary stress and anxiety and more invasive procedures. Although multiple testing procedures accompany mammograms during cancer diagnosis, the increase use of mammogram inadvertently increases overdiagnosis, which could potentially harm the patient. The extend to which mammogram increase overdiagnosis of breast cancer is still debated and different studies report estimates of less than 5% to more than 50%, depending on differences in populations, methodologies, and assumptions . On the flip side, there’s no denying the benefits of mammogram on early cancer detection and chances of treatment success.
At the end of the day, does the benefit of mammogram screening outweigh the harm?
- American Cancer Society. Survival Rates for Breast Cancer. September 20, 2019.
- Welch, H.G., et al., Breast-Cancer Tumor Size, Overdiagnosis, and Mammography Screening Effectiveness. New England Journal of Medicine, 2016. 375(15): p. 1438-1447.
- Oeffinger, K.C., et al., Breast Cancer Screening for Women at Average Risk: 2015 Guideline Update From the American Cancer Society. Jama, 2015. 314(15): p. 1599-614.
- National Breast Cancer Foundation. Biopsy. Available from: https://www.nationalbreastcancer.org/breast-cancer-biopsy.
- Pace, L.E. and N.L. Keating, A systematic assessment of benefits and risks to guide breast cancer screening decisions. Jama, 2014. 311(13): p. 1327-35.