Risk of developing a second primary cancer in male breast cancer survivors: a systematic review and meta-analysis

BACKGROUND: With increasing survival after cancer diagnoses, second primary cancers (SPCs) are becoming more prevalent. We investigated the incidence and site of non-breast SPC risks following male breast cancer (BC). METHODS: PubMed, Embase and Web of Science were systematically searched for studies reporting standardised incidence ratios (SIRs) for SPCs published by March 2022. Meta-analyses used the generic inverse-variance method, assuming a random-effects model. We evaluated SIRs for overall SPCs, site-specific risks, by age at BC onset, time since BC onset and geographic region. We assessed study quality using routine techniques. RESULTS: Eight population-based retrospective cohort studies were identified. SIRs ranged from 1.05 to 2.17. The summary SIR estimate was 1.27 (95% CI: 1.03–1.56, I(2): 86%), and there were increased colorectal (SIR: 1.29, 95% CI: 1.03–1.61), pancreatic (SIR: 1.64, 95% CI: 1.05–2.55) and thyroid (SIR: 5.58, 95% CI: 1.04–30.05) SPC risks. When an outlying study was excluded, the summary SIR for men diagnosed with BC before age 50 was 1.50 (95% CI: 1.21–1.85), significantly higher than men diagnosed at older ages (SIR: 1.14, 95% CI: 0.98–1.33). CONCLUSIONS: Male BC survivors are at elevated risks of developing second primary colorectal, pancreatic and thyroid cancers. The estimates may assist their clinical management and guide decisions on genetic testing.