Clinical:Case Study: Mammograms

Original materials created in October 2002 by Kate Patterson Neely, M.D.

History

SL is a 48y/o African American woman who presents for a well-woman visit. She gets regular well care, including clinical breast exam (CBE), but is quick to apologize for not having gotten a mammogram, which she “knows she should have done.” She does irregular self breast exams (SBE), and feels guilty when she doesn’t do them but anxious when she does. No previous breast lumps or biopsies. She has three children, whom she breast fed for a combined total of 19 months. She works as a secretary. Infrequent exercise. No tobacco, alcohol, or recreational drugs. No family history of breast or ovarian cancer.

Exam

Vital signs, including menses, are normal, as are breast and pelvic exams.

Discussion

The prospect of developing breast cancer causes fear and anxiety in women. While each year more women will die of heart disease, most of us are more scared of breast cancer. As a country, we have done a remarkable job at educating women about the prevalence of breast cancer, and implementing mammography screening. Unfortunately, the experts still don’t agree about whether mammography really saves lives.

In 1997, the NIH Consensus Development Conference, after reviewing the evidence, decided screening was not indicated for women <50y/o. Despite this conclusion, the National Cancer Advisory Board, with significant pressure from congress and consumer advocacy groups, advised the National Cancer Institute (NCI) to recommend screening. The NCI complied, thus, the recommendations that we use aren’t based on science, but on consumer and political pressure. Unfortunately, the science hasn’t become any more convincing.

From the practitioner perspective, successful screening requires three things: 1) accurate early detection must be feasible; 2) early detection must improve outcomes; and 3) benefit of screening must outweigh harm; because mammography’s follow-up testing is fairly invasive, it is imperative that this latter criterion is met.

From a consumer perspective, the primary purpose of mammography is to relieve anxiety. Women want to know that they don’t have breast cancer, and they want the blessing blessing of ongoing good health. Early detection and treatment of breast cancer is the dreaded, not the hoped-for, outcome.

It may be that mammography meets neither the consumer, nor the practitioner criteria for a successful screening tool.

The literature reveals that in women under 50y/o, mammography detects 51-83% of malignancy. Over 50y/o, this improves very slightly, to 56-86%. Obviously, this range is huge, and dependent on a variety of factors, adding credence to the claim that mammography provides suboptimal screening. This creates a false sense of security among practitioners and patients. Recent meta-analyses of the screening literature triggered reassessments of guidelines by the NCI and the United States Preventive Services Task Force (USPSTF).

The USPSTF found fair evidence (class B) that mammography screening every 12 - 33 months significantly reduces mortality from breast cancer. They downgraded the recommendation for the 50-69y/o women from class A to class B, in agreement with the literature. But for the younger and older women, they upgraded the recommendation from class C to class B, with no new evidence on which to base the change. However, they do state that “for women aged 40-49, the evidence is weaker, and the absolute benefit of mammography is smaller. The precise age at which the potential benefits of mammography justify the possible harms is a subjective choice.”

The NCI’s Physician’s Data Query came to different conclusions. They reported that while mammography detects lesions smaller than those detected by other means, it is associated with more diagnostic testing, treatment and anxiety, and it may lead to overdiagnosis and unnecessary treatment. The study results are inconsistent, and existence of benefit is uncertain. “In conclusion, screening for breast cancer does not affect overall mortality, and the absolute benefit for breast cancer mortality appears to be small.”

In September of this year, following the guideline changes, the Canadian National Breast Cancer Screening Study-1 was published. After 11 to 16 years of followup, 4 or 5 mammograms, CBE, and BSE had not reduced breast cancer mortality compared with usual community care in 50,000 40-49 year olds.

Most “positive” mammograms do not detect malignancy, making the risk for unnecessary intervention significant. The positive predictive value for women 40-49 y/o is 1-4%, gradually increasing to 18-20% by age 70. Six and a half percent of screening mammograms require follow-up: repeat mammograms, ultrasound, and/or biopsy. Positive mammograms (remember, mostly false positives) invoke terror in women. Over a 10 year period 23% of screened women will have had an abnormal mammogram. The cumulative risk of a false positive after 10 annual mammograms is 49%.

The radiation exposure from annual mammograms of 100,000 women for 10 years is predicted to cause 8 radiation-induced deaths from breast cancer. This might be acceptable if there are more lives saved, but the evidence doesn’t show that yet.

Plan

I explained to SL that until recently, the best scientific analysis did not recommend screening mammography until age 50, although groups like the American Cancer Society did. For reasons I don’t understand, the USPSTF now does recommend offering screening every 12-33 months to women 40-49. However, the new evidence still shows that it may or may not have benefit.

We discussed SL’s personal risk of breast cancer, notably the lack of family history, the 7% decreased risk for each of her pregnancies, and the 4.3% decreased risk for each 12 months of breastfeeding. We discussed the risk of false positive tests, 1 in 15 women, and the exposure to radiation. Finally, I used a risk calculator to discover that this patient’s 5 year risk of breast cancer is 0.5%, and her lifetime risk is about 5%, not including the benefit from breast feeding, which is not included in the calculations. She agreed to consider this information, and we plan to discuss it again in a month.

SL returned in one month and decided to wait until she is fifty to get a mammogram. I suggested that we revisit the decision briefly at each annual visit, as the evidence changes. I also explained that diagnostic mammography- if she finds a lump- is a different situation, and I encouraged her to bring any breast changes to my attention, whether found through self breast exam or by accident.

References

Collaborative Group on Hormonal Factors in Breast Cancer, Breast Cancer and Breast Feeding, Lancet 2002; 360:187-95.

Humphrey L, et al. Breast Cancer Screening: A Summary of the Evidence for the U.S. Preventative Services Task Force, Ann Intern Med. 2002;137:347-360.

National Cancer Institute, Breast Cancer (PDQ): Screening, Health Professional Version, Cancer.gov [last modification 09/2002].

Elmore JG, et al. Ten-Year Risk of False Positive Screening Mammograms and Clinical Breast Examinations New Engl J Med. 1998;338:1089-96.