Patterns of subsequent cancer incidence over time in patients with breast cancer.

Abstract

Breast cancer survivors face a higher risk of subsequent primary cancers. This study investigated the patterns of subsequent cancer risk according to time since breast cancer diagnosis. Using data from the Surveillance, Epidemiology, and End Results program (2000-2018), we identified a cohort of 771,681 breast cancer survivors. Standard incidence ratios (SIR) were calculated by comparing the observed to the expected number of subsequent cancers over different follow-up periods since breast cancer diagnosis. Analyses were conducted for multiple cancer types, stratified by hormone receptor (HR) status and treatment of the first breast cancer, age, and race/ethnicity. Survivors experienced a 16% increased risk of subsequent cancer with the SIR continuing to increase with longer follow-up (SIR=1.04, 1.22, and 1.31 for 12-59, 60-119, and ≥120 months). This trend was driven primarily by a subsequent breast cancer, particularly among women <50 years, those with initial HR-negative cancer, and racial/ethnic minorities. The patterns of subsequent non-breast cancer risk varied by type. An early-onset and sustained increased risk was observed for subsequent leukemia, thyroid, soft tissue, melanoma, pancreas, and uterine cancer. A delayed increased risk was observed for subsequent esophagus, ovarian, oral cavity/pharynx, and lung cancer, while for small intestine, stomach, kidney, and colorectal cancer there was a decrease after an initial increased risk. Patterns in subsequent cancer risk since breast cancer diagnosis differ by cancer type and characteristics of the first breast cancer. These findings can inform etiology and tailored approaches to screening and prevention of subsequent cancers.