Sturz, Jenna L.

ABSTRACT Background and Objectives Surgical management of ipsilateral breast tumor recurrence (IBTR) is often mastectomy. No guidelines specifically address contralateral prophylactic mastectomy (CPM) for this population. We assessed factors associated with CPM at the time of IBTR mastectomy. Methods Patients undergoing mastectomy for IBTR (10/2008‐5/2024) were identified. Demographics, tumor characteristics, and treatment details were assessed. Results Of the 381 eligible IBTR patients, 221 (58.0%) had a unilateral therapeutic mastectomy and 160 (42.0%) underwent mastectomy with CPM. CPM patients were younger ( p < 0.0001), with lower clinical T category tumors ( p < 0.001) and less HR + HER2‐ invasive disease ( p = 0.004). CPM patients were more likely to undergo germline genetic testing (63.1% vs 41.6%, p < 0.0001) and were twice as likely to have immediate breast reconstruction ( p < 0.0001). On multivariable analysis, younger age, HR‐HER2 + IBTR subtype, pathogenic variants known at the time of surgery (relative to negative testing and/or no genetic testing), immediate breast reconstruction, and prior radiation for index cancer were each associated with CPM (all p < 0.05). Conclusion In our series of 381 patients treated with mastectomy for IBTR, 42% also had a CPM. Multiple factors, including age, tumor stage and biology, immediate breast reconstruction, and genetic testing may impact CPM choice.