Blog | Friday, October 21, 2011

NEJM review on breast cancer screening gets to the nitty-gritty of false positives

With little fanfare, the New England Journal of Medicine published a feature on breast cancer screening in its Sept. 15 issue. The article, like other vignettes in the NEJM, opens with a clinical scenario. This time, it's a 42-year-old woman who is considering first-time mammography.

The author, Ellen Warner, MD, an oncologist at the University of Toronto, takes opportunity to review updated evidence and recommendations for screening women at average risk for the disease. She outlines the problem: "Worldwide, breast cancer is now the most common cancer diagnosed in women and is the leading cause of deaths from cancer among women, with approximately 1.3 million new cases and an estimated 458,000 deaths reported in 2008.(1)

On screening: "The decision to screen either a particular population or a specific patient for a disease involves weighing benefits against costs. In the case of breast-cancer screening, the most important benefits are a reduction in the risk of death and the number of life-years gained ..."

She breaks down the data for mammography by age groups: "For women between the ages of 50 to 69 the evidence is clear, she says. For those over 70, there are little data to support breast cancer screening. There's a consensus that screening isn't appropriate for women with serious coexisting illnesses and a life expectancy of less than 5-10 years."

For those between the ages of 40-49, Warner challenges the revised 2009 USPSTF recommendations on several counts. She critiques those authors' weighting of data from the Age trial of 161,000 women, emphasizing the use of an antiquated (single view) mammography technique and flawed statistics. She considers: "... However, this change in remains highly controversial,22, 23 especially because of the greater number of years of life expectancy gained from preventing death from breast cancer in younger women. According to statistical modeling,19 screening initiated at the age of 40 years rather than 50 years would avert one additional death from breast cancer per 1000 women screened, resulting in 33 life-years gained."

What I like about Warner's analysis, besides its extreme attention to details in the data, is that she's not afraid to, at least implicitly, assign value to a procedure that impacts a young person's life expectancy relative to that of an older person.

She goes on to consider digital mammography and the Digital Imaging Screening Trial (DMIST [NCT00008346]) results. For women under 50 years, digital mammography was significantly more sensitive than film (78% vs. 51%).

The article is long and detailed; I recommend the full read including some helpful tables, with references to the major studies, and charts.

In concluding, the author, who admits receiving grant support from Amersham Health (a GE subsidiary), consulting fees from Bayer and lecture fees from AstraZeneca, returns to the hypothetical patient, and what might be said to a woman in her 40s who lacks an outstanding risk (such as a genetic disposition or strong family history): "... Mammography screening every 2 years will find two out of every three cancers in women her age, reduce her risk of death from breast cancer by 15%. There's about a 40% chance that further imaging (such as a sonogram) will be recommended, and a 3% chance for biopsy with a benign finding ..."

In my opinion, this is key, that the chances of a false positive leading to biopsy are only 3% for a woman in her 40s. If those biopsies are done in the radiology suite with a core needle, every 2 years for women of average risk, the costs of false positives can be minimized.

This post originally appeared at Medical Lessons, written by Elaine Schattner, ACP Member, a nonpracticing hematologist and oncologist who teaches at Weill Cornell Medical College, where she is a Clinical Associate Professor of Medicine. She shares her ideas on education, ethics in medicine, health care news and culture. Her views on medicine are informed by her past experiences in caring for patients, as a researcher in cancer immunology and as a patient who's had breast cancer.