BOSTON--Previous study results showing that screening mammography
is beneficial only in women over age 50 may stem from inappropriate
grouping of age-based data rather than an actual change in benefit
at age 50, Daniel B. Kopans, MD, and his colleagues assert in
a new study.
"Our study, and careful review of other studies, shows that
there is no abrupt change in the diagnosis of breast cancer detected
by mammography at any age, but rather a steady increase in detection
as one would expect, since the incidence of breast cancer increases
with age," Dr. Kopans says.
Based on an analysis of data from the Breast Cancer Screening
Program at the University of California at San Francisco, Kerli-kowske
et al recommended screening mammography for all women aged 50
or older but only for high-risk women aged 40 to 49 (JAMA 270:2444-2450,
1993). However, Dr. Kopans points out that the authors reached
this conclusion by comparing data from women aged 30 to 49 with
those from women aged 50 to 70 or more.
This inappropriate grouping of extremes, he says, skewed the results,
causing the appearance of an abrupt change at age 50 instead of
Such inappropriate groupings are generally done because there
are not enough women in the study to analyze the data by smaller
age increments. In the San Francisco study, women aged 30 to 39
who have a very low prevalence of cancer were grouped with those
aged 40 to 49, while women aged 70 and older who have a very high
prevalence were grouped with 50 and 60 year olds.
But even grouping women into ages by decades is too broad to show
the actual gradual increase in the ability of mammography to find
cancer with increasing age, Dr. Kopans argues.