The American Society of Breast Surgeons held its 2011 annual meeting in D.C. from April 27 – May 1. Among the papers presented was Abstract #1754: “Mammography in 40 Year Old Women: The Potential Impact of the U.S. Preventative Services Task Force (USPSTF) Mammography Guidelines.” You can find the press release, followed by the abstract, here. The main result was that screening women ages 40-49 by mammography was associated with finding smaller tumors, with less spread to the lymph nodes, than clinical breast exams alone, and this correlates with improved survival at 5 years.
The study, put forth by a group at the University of Missouri-Columbia in Columbia, MO, is based on a 10-year retrospective chart review, from 1998 – 2008, of 1581 women treated for breast cancer at that institution. In this author’s opinion, a retrospective, chart-review type analysis of a medical intervention is about as low as you can get on the quality-of-data scale in a medical study. And, as emphasized by Dr. Otis Brawley, chief medical officer of the ACS as quoted in HeathDay’s report on the matter, these are tentative findings, presented in abstract form at a meeting. He suggested that the 5-year follow-up is too short.
That said, I think the findings are significant and likely reflect what happens when mammography screening is done right, which is that it saves lives in women 40 and older.
The results focused on the 320 women – 20% of all those treated for breast cancer at the institution – between the ages of 40 and 49 at the time of breast cancer diagnosis. Among those, mammography detected the tumors in just under half (47%) of the cases; in 53%, there was a palpable mass – the “clinical detection” group. In those with cancers were detected by mammography, the average tumor size was 2 cm in diameter; in the clinical detection group, the average size was 3 cm. (From an oncologist’s perspective that’s a huge difference; for most breast cancer subtypes that 1 cm difference in diameter portends a distinct prognosis.) What’s more, the frequency of lymph node involvement in the clinical detection group was 56%, more than twice that in the mammography group (25%), another prognosis-changer. These findings were highly significant from a statistical perspective, with p-values <0.0001.
The researchers confirmed that negative lymph nodes and smaller tumors were associated with longer survival. They estimated that disease-free survival, at five years, was 94 percent for women under 50 who received mammograms and 78 percent for those who did not receive the screening exams. Five year overall survival rates for each group were 97% and 78%, respectively.
These figures have huge implications, especially if you multiply the potential survival benefit – on the order of 20 percent at 5 years, or greater, depending on how you look at it – across over some 21.5 million women in the U.S. between the ages of 40 and 50, approximately 1.5 in 1000 of whom will be found to have invasive BC per year.*
Reuters ran this story on April 29 as did HealthDay. Both ran quotes by Dr. Paul Dale, chief of surgical oncology at the University of Missouri School of Medicine and lead author of the abstract. The findings suggest that adherence to the updated U.S. Preventive Service Task Force (USPSTF) guidelines, which do not recommend screening mammography for most women between the ages of 40 and 49, would lead to preventable deaths.
One thing the author of ML learned this morning is that Dr. Virginia Moyer, the new chair of the USPSTF and who is quoted in the HealthDay coverage, is a pediatrician and professor with a public health degree.