Bilateral risk-reducing nipple-sparing mastectomy with implant-based reconstruction after previous breast-conserving treatment including radiotherapy: an exploratory multicenter cohort study

Nipple-sparing mastectomy (NSM) with implant-based reconstruction is increasingly used in prophylactic settings. Outcomes after previous breast-conserving treatment (BCT) including radiotherapy remain uncertain. This exploratory retrospective multicenter cohort included asymptomatic patients with pathogenic germline mutations who underwent bilateral risk-reducing NSM with immediate implant-based reconstruction at 12 Brazilian institutions. The exposure was previous BCT including radiotherapy, rather than radiotherapy alone. The primary outcome was the occurrence of at least one early postoperative complication. Secondary outcomes included capsular contracture, additional reconstructive procedures, descriptive burden of complication events and retrospectively assessed aesthetic outcomes. Analyses were performed at the patient level. Modified Poisson regression with robust variance was used in an exploratory adjusted analysis. Among 219 patients, 20 (9.1%) had previous BCT including radiotherapy. Early postoperative complications occurred in 5/20 exposed patients (25.0%) and 47/199 unexposed patients (23.6%; p = 0.88). The descriptive event-based rates were 0.50 and 0.26 early complication events per patient in the exposed and unexposed groups, respectively; this analysis was descriptive only and no inferential comparison was performed. In the exploratory adjusted analysis, previous BCT including radiotherapy was not associated with early postoperative complications (adjusted RR 0.64, 95% CI 0.16–2.60; p = 0.53), although the estimate was imprecise. No statistically significant differences were detected in capsular contracture or the ordinal aesthetic assessment. Additional procedures included planned and elective aesthetic-reconstructive interventions and were not interpreted as complication-related reoperations. Aesthetic findings were limited by retrospective institutional assessment and missing data, particularly in the unexposed group. In this exploratory patient-level multicenter cohort, no statistically significant increase in complications was detected among carefully selected mutation carriers with previous BCT including radiotherapy. However, clinically relevant differences cannot be excluded because of the small, exposed cohort, retrospective selection, patient-level analysis, potential breast-level exposure misclassification, missing aesthetic data, and wide confidence intervals. These findings should be hypothesis-generating.