Background: Among women who practice breast self-examination (BSE), breast cancers may be detected when they are at an earlier stage and are smaller than in women who do not practice BSE. However, the efficacy of breast self-examination for decreasing breast cancer mortality is unproven. This study was conducted to determine whether an intensive program of BSE instruction will reduce the number of women dying of breast cancer.
Methods: From October 1989 through October 1991, 266,064 women associated with 519 factories in Shanghai were randomly assigned to a BSE instruction group (132,979 women) or a control group (133,085 women). Initial instruction in BSE was followed by reinforcement sessions 1 and 3 years later, by BSE practice under medical supervision at least every 6 months for 5 years, and by ongoing reminders to practice BSE monthly. The women were followed through December 2000 for mortality from breast cancer. Cumulative risk ratios of dying from breast cancer were estimated using Cox proportional hazards models. All statistical tests were two-sided.
Results: There were 135 (0.10%) breast cancer deaths in the instruction group and 131 (0.10%) in the control group. The cumulative breast cancer mortality rates through 10 to 11 years of follow-up were similar (cumulative risk ratio for women in the instruction group relative to that in the control group = 1.04, 95% confidence interval = 0.82 to 1.33; P =.72). However, more benign breast lesions were diagnosed in the instruction group than in the control group.
Conclusions: Intensive instruction in BSE did not reduce mortality from breast cancer. Programs to encourage BSE in the absence of mammography would be unlikely to reduce mortality from breast cancer. Women who choose to practice BSE should be informed that its efficacy is unproven and that it may increase their chances of having a benign breast biopsy.