Cancer Screening Programs May Be Less Effective
Cancer screening programs might be less effective than previously thought, according to a study conducted by researchers at the Harvard School of Public Health and the Oslo University Hospital in Norway. The study, published in the New England Journal of Medicine last week, used data from four groups of Norwegian women diagnosed with breast cancer.
Researchers found a 4.8 decrease in the number of deaths from breast cancer per 100,000 person-years in the group of women followed from 1996 to 2005 not offered mammograms versus women in another non-screening group followed from 1986 to 1995. They found a decrease of 7.2 per 100,000 person-years in the 1995 to 2005 group who were offered mammograms compared to the 1986 to 1995 group.
Person-years refers to the number of people in the study cohort times the number of years they were followed.
School of Public Health Professor and lead author of the study Marvin Zelen said he was aware that his team’s findings would be controversial, but that the study was not criticizing the effectiveness of the mammogram itself.
But Daniel B. Kopans ’69, a professor of radiology at Harvard Medical School, said that the study slights the real benefits of mammograms.
According to Kopans, one of the major flaws of the study was that it followed women for 2.2 years after they were diagnosed with breast cancer, counting only those who died within those 2.2 years as a death.
“This is a trivial amount of follow-up for almost any cancer study, but for breast cancer it is totally unsupportable,” Kopans wrote in an e-mail. “Mammography does not save lives instantaneously. With breast cancer at least 5-10 years of follow-up are needed to have legitimate data.”
Kopans also criticized the fact that while Norwegian breast cancer data is available through at least 2008, the present study stops at 2005.
“The New England Journal has had a major, undeclared, publication bias, since 1993, against mammography screening, but particularly with regard to screening women in their forties,” Kopans wrote.