Population incidence and characteristics of secondary breast cancer after uterine cancer: a competing risk analysis

Purpose: To examine incidence and characteristics of women who developed secondary breast cancer after uterine cancer.

Methods: This is a population-based retrospective cohort study utilizing the National Cancer Institute's Surveillance, Epidemiology, and End Result Program from 1973 to 2013. Women with uterine cancer who did not have synchronous or a history of breast cancer were followed after their uterine cancer diagnosis (N = 236,561). A time-dependent competing risk analysis was performed to examine cumulative incidences and clinico-pathological characteristics of those who subsequently developed breast cancer.

Results: There were 7110 (3.0%) women who developed secondary breast cancers after uterine cancer with 5-, 10-, and 20-year cumulative incidence rates of 1.5, 2.8, and 4.7%, respectively. The increase in the rate of secondary breast cancer was particularly high in the first 3 years after a uterine cancer diagnosis (annual percent change [APC] 4.9), followed by 3-7 years (APC 1.6) after diagnosis (P < 0.001). The median time to develop secondary breast cancer was 6.4 years. Older women had significantly shorter time intervals between uterine and breast cancer diagnoses (3.7 years for aged > 71, 5.9 for aged 64-71, 7.6 for aged 56-63, and 9.4 for aged < 56, P < 0.001). In a multivariable analysis, older age, White race, married status, endometrioid, serous, and mixed histology types, and early-stage tumors remained as independent factors of developing secondary breast cancer (all, P < 0.05).

Conclusion: Tumor factors with endometrioid and serous histology types and early-stage disease were the factors associated with secondary breast cancer after uterine cancer diagnosis. Older women had shorter time to develop secondary breast cancer.