Risk of second primary breast cancer among cancer survivors: Implications for prevention and screening practice.

Second primary breast cancer (SPBC) is becoming one of the major obstacles to breast cancer (BC) control. This study was aimed to determine the trend of SPBC incidence over time and the risk of developing SPBC in site-specific primary cancer survivors in the United States. The Surveillance, Epidemiology, and End Results (SEER) 13 registry (1992-2015) was used to identify SPBC patients with previous malignancies. Standardized incidence ratio (SIR) was computed to compare the incidence rates of the observed cases of SPBC in cancer survivors over the expected cases in the general population. Elevated risk of SPBC was observed in women with previous BC (SIR = 1.74) or thyroid cancer (SIR = 1.17). Women with initial skin melanoma in older age (≥50 years) (SIR = 1.11), or White race (SIR = 1.11) presented an elevated incidence of SPBC than the general female population. Besides, Asian/Pacific Islander (API) women with cancer of corpus uteri, ovary, bladder, or kidney were prone to developing SPBC when compared with the general population, with SIRs of 1.61, 1.35, 1.48, and 1.70, respectively. Male BC patients showed profound risk of developing SPBC (SIR = 34.86). Male leukemia patients also presented elevated risk of developing SPBC (SIR = 2.06). Our study suggests significant increase of SPBC in both sexes in the United States. Elevated risk of SPBC exists in survivors with primary BC, female thyroid cancer, male leukemia, and API female cancer patients with primary genitourinary cancer. Our study is helpful in developing strategies for BC control and prevention on specific first primary cancer survivors with an elevated risk of SPBC.