Effect of screening mammography on breast cancer survival in comparison to other detection methods: a retrospective cohort study

Abstract

The effectiveness of screening mammography (SMG) on mortality has been established in randomized controlled trials in Western countries, but not in Japan. This study evaluated the effectiveness by comparing the survival based on detection methods. The survivals were estimated by the Kaplan-Meier method. Breast cancer patients diagnosed from 1 January 1989 to 31 December 2000 were determined using the Miyagi Prefectural Cancer Registry and follow-up was performed from the date of the diagnosis until the date of death or the end of follow-up, 31 December 2005. The hazard ratios (HR) and 95% confidence interval (CI) of breast cancer death based on the detection methods were estimated by the Cox proportional-hazard regression model. The mean age of the 7513 patients was 55.7 years (range, 15.0-99.3). The 5-year survival associated with the SMG group, the clinical breast examination (CBE) group, and the self-detection group was 98.3%, 94.3%, and 84.8%, respectively. The HR (95% CI) of deaths from breast cancer was 2.50 (1.10-5.69) for patients in the CBE group and 6.57 (2.94-14.64) for the self-detection group in comparison to the SMG group. In women aged 50-59, the HRs were 1.64 (0.58-4.62) among the CBE group and 3.74 (1.39-10.03) among the self-detection group, and the HRs for the CBE and self-detection groups in women aged 60-69 were 2.96 (0.68-12.83) and 9.51 (2.36-38.26), respectively. After adjusting for stage, the HRs dropped remarkably. Screening mammography may be more effective in the elderly group and be able to reduce the mortality of breast cancer in Japan.

Figure 1

Kaplan–Meier survival curves for screening mammography (SMG) (179 patients), clinical breast examination (CBE) (1173 patients), and self‐detection (4924 patients) (*,**log‐rank test). Statistically significant differences were thus observed between SMG and self‐detection (P < 0.0001), CBE and self‐detection (P < 0.0001), and SMG and CBE (P = 0.023).