Breast Cancer: Risks and Screening
Early Detection Saves Lives, but Debate about Screening Persists
Aug 6, 2008
Breast cancer killed nearly 41,000 American women in 2006. Every three minutes, another woman acquires this devastating diagnosis. In 1960, the incidence of breast cancer was one in twenty; today it is one in eight.
The exact cause of breast cancer is not known; with early detection, it is eminently treatable. Unfortunately, disagreement exists as to who gets screened, and how.
Risk Factors for Breast Cancer
- Age is the most significant single risk factor contributing to the development of breast cancer. Most cases occur in women over 50 years of age; women over 60 are in the highest risk group.
- A woman’s risk for developing breast cancer increases if one first-degree relative (mother, sister, daughter) or if two or more other close relatives, such as cousins, have a history of the disease. Notably, 85% of women who are diagnosed with breast cancer have no family history.
- Mutations in certain genes, such as BRCA1 and BRCA2, increase a woman’s susceptibility to breast cancer. Specialized tests are available to detect these abnormal genes.
- Obesity, high dietary fat intake, heavy alcohol consumption (more than two drinks daily) and smoking are all risk factors for breast cancer.
- High or prolonged exposure to estrogen increases the risk for breast cancer. Hormone replacement therapy (HRT), early puberty, and late childbearing have been linked to breast cancer.
- A woman who develops cancer in one breast has a statistically higher risk of developing cancer in the opposite breast.
Screening
Screening recommendations for breast cancer have long been a matter of debate. Until recently, most experts advised regular breast self-examination (BSE) coupled with screening mammography and clinical breast examination (CBE). Women at risk or with suspicious findings on initial examination underwent more extensive evaluation.
Unfortunately, breast cancer is not a uniform entity, and that lends a great deal of uncertainty to screening and treatment methods. For example, ductal carcinoma in situ (DCIS)—a form of cancer usually detected by mammography—progresses to invasive cancer in less than 50% of cases, yet all women with DCIS get aggressive treatment. An unknown number of these cases thus represent “overtreatment.”
Furthermore, each of the currently-used screening modalities has its own “false-positive” rate. For a given number of women who undergo screening, a certain percentage will exhibit suspicious results that feed them into the next tier on the screening or treatment algorithm. A suspicious finding that is ultimately determined to be benign causes untold emotional upheaval, not to mention exposure to medical manipulations (repeat mammography, biopsy, etc).
Recent reviews have cast doubt on the value of traditional screening methods. Large, well-designed studies have shown that BSE does not reduce mortality. However, 10% of breast cancers that are “radiographically silent” (not detectable on mammogram) can be felt on clinical breast examination. Because the accuracy of BSE depends on the time spent (that is, the diligence of the patient), and since many women aren’t proficient with BSE, many experts now recommend against regular self examination.
The US Preventive Services Task Force still recommends screening mammography for healthy women over 40 years of age, but mammography is less sensitive in younger women, some of whom may be at high risk for breast cancer. Digital mammography increases sensitivity, but studies have not shown a mortality benefit.
Magnetic resonance imaging (MRI) is a promising screening tool for high-risk women, but this modality is not recommended for the general population due to its cost and high false-positive rate.
The one certain thing about breast cancer screening recommendations is the likelihood that they’ll change. Current consensus is:
- The use of mammography and clinical breast examination in women 40 to 49 years of age shows equal benefits and harm. Women in this age group should discuss screening with their physicians, and a case-by-case decision should be made.
- Mammography and CBE in women 50 to 70 years of age should be encouraged, as benefits outweigh risks. Biennial screening is recommended.
- Women 70 and older should be given the option of periodic screening, as risks and benefits of screening in this age group are still unclear.
- Breast self-examination is not recommended in any age group.
- Women at high risk (strong family history of breast cancer or positive genetic screens) should be offered MRI and/or digital mammography, though insufficient evidence exists to recommend their use.
In essence, all women should take the opportunity to discuss their options with a physician who is willing to talk, rather than one who reflexively orders traditional screening examinations.
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