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Background: Contralateral mastectomy (CM) has recently been shown to be associated with survival benefit in women with breast cancer. The objectives of the present study were to describe factors predictive of CM in young women (≤35 years old) with invasive breast cancer and evaluate its impact on survival, in a large population based cohort. Methods: All women diagnosed with invasive breast cancer aged ≤35 from 1994 – 2003 treated with mastectomy were identified from the Ontario Cancer Registry. Patient demographics, complete tumour and treatment characteristics were abstracted from primary chart review. Cox proportional hazard regression was performed to assess factors associated with performance of CM and its effect on recurrence and overall survival, performance of CM was modeled as a time varying co-variate. The models were controlled for known predictors including age, tumor size, nodal status, ER/PR, LVI, histologic grade, systemic therapy and adjuvant radiation. Results: There were 628 women identified. Of these, 101 underwent a CM (16.1%). On multivariable analysis, factors predictive of CM were negative lymph node status (HR: 1.74, 95% CI [1.052-2.872]; p-value = 0.031) and negative estrogen receptor status (HR: 2.7, 95% CI [1.314-5.736]; p-value = 0.007). After a median follow up of 11 years, no significant survival benefit was observed in women undergoing CM compared to those who did not (HR: 0.95, 95% CI [0.61-1.46], p-value = 0.80). Conclusions: Performance of CM in young women with invasive breast cancer did not result in a significant survival benefit, compared to those without CM. Factors found to be predictive of performance of CM negative lymph node status and negative estrogen receptor status. Further studies are needed to determine if a subset of young women might benefit from CM.
