Background: The effect of mammography screening on breast carcinoma mortality in women ages < 50 years remains unclear.
Methods: A randomized trial of invitation to breast carcinoma screening with mammography was performed in the city of Gothenburg, Sweden. The purpose was to estimate the effect of mammographic screening on breast carcinoma mortality in women ages < 50 years. Randomization was initially by day-of-birth cluster (18% of subjects), and subsequently by individual (82% of subjects). Between September 1983 and April 1984, 11,724 women ages 39-49 years were randomized to the study group. This group was invited to mammographic screening every 18 months. Two-view mammography was used at each screen unless the density of the breast at the previous screen indicated that single view was adequate. Fourteen thousand two hundred and seventeen women in the same age range were randomized to a control group that was not invited to undergo screening until the fifth screen of the study group (between 6 and 7 years after randomization). Women with breast carcinoma diagnosed up to the time immediately after the first screen of the control group were followed for death from breast carcinoma until the end of December 1994.
Results: A 45% reduction in mortality from breast carcinoma was observed in the study group compared with the control group (relative risk [RR] = 0.55, P = 0.035, 95% confidence interval [CI], 0.31-0.96). A conservative estimate based on removal of the tumors detected at the first screen of the control group gave a mortality reduction of 44% (RR = 0.56, P = 0.046, 95% CI, 0.31-0.99). In both cases, the effect was statistically significant.
Conclusions: Mammographic screening can reduce mortality from breast carcinoma in women ages < 50 years. The mortality reduction can be substantial if high quality mammography is used and an 18-month interscreening interval is strictly adhered to.