Screening for Breast Cancer and Prostate Cancer: An Alternative View

In an article in the Journal of the American Medical Association [2009;302(15):1685-1692], Laura Esserman, MD, MBA, Yiwey Shieh, and Ian Thompson, MD, offer insight into the thinking behind screening for breast cancer and prostate cancer. They note that those 2 cancers account for 26% of all cancers in the United States, with approximately 194,280 patients diagnosed with breast cancer and approximately 192,280 patients diagnosed with prostate cancer each year.

The outcomes for localized versus advanced disease are widely different: breast cancer 5-year survival rates are 98.1% versus 27.1%, respectively. Survival rates at 5 years for prostate cancer are 100% versus 31.7%, respectively, for localized and advanced disease. On the assumption that early detection and treatment will increase survival rates, screening for both cancers has been vigorously promoted.

Approximately 70% of women >49 years of age report having had a mammogram recently, and approximately 50% of men at risk for prostate cancer have had a routine prostate-specific antigen (PSA) test. The screening for both diseases in the past 20 years has resulted in a significant increase in early detection; PSA testing has increased 2-fold the likelihood that a man will be diagnosed with prostate cancer in his lifetime. In 1980, lifetime risk for a white man developing prostate cancer was 1 in 11. Today it is 1 in 6. Likewise, in 1980, a woman had a lifetime risk of developing breast cancer of 1 in 12. Today it is 1 in 8.

The authors contend that the increase in detection of early cancers is not necessarily beneficial, noting that the emphasis on breast cancer and prostate cancer has resulted in an increase in early and overall cancer rates, with some decrease in regional stage disease. After 20 years of screening, the authors state that “it is disappointing that the absolute numbers of more advanced disease have not decreased nearly as much as hoped for either cancer.” They add that while mortality for both cancers has decreased, the role of screening in that decline has not been established.

In explaining why screening has not led to greater reduction in mortality from breast and prostate cancer, the authors said that (1) screening increases the detection of indolent cancer and (2) screening probably misses the most aggressive cancers. They added that while screening finds slower growing and potentially indolent tumors and finds some progressive cancers early, screenings are not done frequently enough to detect lethal tumors in time to prevent death. The inability to differentiate between cancers that pose minimal risk from those that pose substantial risk, the population is at increasing risk for overtreatment of breast or prostate cancer.

A recent study compared incidence and mortality associated with prostate cancer at a site in Connecticut, where rates of PSA screening are low, and a site in Seattle, Washington, where PSA screening rates are high. The study found that while there were significantly higher rates of incidence of prostate cancer and treatment for the disease, the higher rates were unrelated to rates of mortality. Furthermore, the authors say that the rate of overdiagnosis in national breast cancer screening programs may be as high as 1 in 3 for invasive cancers.

The authors acknowledge that screening is effective when premalignant lesions are detected and removed, such as adenomatous polyp removal during colonoscopy screening or cervical intraepithelial neoplasia ablation by colposcopy following detection with a Pap smear. Those screenings have resulted in significant decreases in colon and cervical cancers, which has not been the case in breast and prostate cancer.

Finally, the authors propose a new approach for the early detection and prevention of breast and prostate cancer: (1) develop and validate markers that identify and differentiate between minimal-risk cancers and cancers that are progressive and pose significant risk, (2) reduce treatment for minimal-risk cancers, (3) develop clinical and patient tools to support informed decisions about treatment, and (4) identify high-risk patients and target preventive interventions. They suggest that there is a need for the creation of projects that encourage innovation in prevention, screening, and management of breast and prostate cancers.

In conclusion, the authors note that “about $20 billion is spent to screen for breast cancer and prostate cancer in the United States. Highly innovative businesses typically invest 10% to 20% of their sales into research and development for the next new product. A similar investment is needed to improve screening, accelerate prevention research, and reduce harm from breast cancer and prostate cancer deaths.”—Tori Socha