Breast cancer patients have a generally increased risk of developing second cancers. The object of this study was to clarify the increased as well as decreased incidence of cancers in breast cancer patients using autopsy cases. 164 211 autopsy cases in the Annual of Pathological Autopsy Cases in Japan from 2002 to 2010 were analyzed for multiple primary cancer (MPC). Female MPC cases (4222 cases) were selected. We investigated the cancer incidence observed in breast cancer associated MPC. The Chi-squared test was used for analysis. All P-values were two-sided, and differences at P < 0.05 were considered significant. Breast cancer associated MPC showed a significantly increased incidence of ovarian, pancreatic, and skin cancer (Odds Ratio [95 % confidence interval (CI)]) = 1.464 [1.03, 2.08], 1.414 [1.08, 1.85] and 2.092 [1.28, 3.41]), and a decreased incidence of colorectal and cervical cancer (OR [95 % CI]) = 0.732 [0.60, 0.90], 0.605 [0.38, 0.96]). Our findings of an increased incidence of malignancies in breast cancer associated MPC cases were consistent with the results of previous population-based studies. This study is the first study to analyze massive autopsy data on MPC which provide new evidence clinically and pathologically.
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