Subsequent primary cancer risk and mortality among premenopausal breast cancer survivors.

Patients with premenopausal breast cancer (preBC) usually have long-term survivorship. However, less is known about the risk pattern of subsequent primary cancer (SPC) and noncancer diseases among them. Here, this study aimed to evaluate the risk of developing SPCs and mortality among preBC survivors. In this population-based, retrospective cohort study, 5-year preBC survivors diagnosed at age 20-59 years during 1992-2014, in the 11 Surveillance, Epidemiology and End Result registries were included. Standardized incidence ratio (SIR) and standardized mortality ratio (SMR) were estimated for SPCs and mortality by cause, respectively. Among 181,947 survivors (mean age at diagnosis, 49.1 years; 65.9% White), there were 12,503 SPC cases, 4,280 SPC-related deaths, and 10,591 noncancer-related deaths. SPC risk was increased compared with the general population (SIR 1.06, [95% CI, 1.04-1.08]). The elevated risk was primarily associated with soft tissue cancer, bones/joints cancer, and acute non-lymphocytic leukemia (SIRs 2.01 [95% CI, 1.73-2.33], 1.78 [95% CI, 1.21-2.53], and 1.68 [95% CI, 1.46-1.93], respectively). Young-onset, Asian survivors, those with hormone receptor-negative BC, and initially treated with chemo-radiotherapy were at high-risk. The risk of dying from SPCs was also increased (SMR 1.07, [95% CI, 1.04-1.10]) and featured with similarly vulnerable subpopulations. Survivors of non-White ethnicity had a higher risk of dying from noncancer diseases. This study highlighted the excess risk of developing and dying from SPCs among preBC survivors, suggesting that targeted healthcare is warranted. Strategies for SPCs and noncancer comorbidity management are in great demand to achieve better long-term survivorship among preBC patients.