Impact of an In Situ Component on Outcome After In-Breast Tumor Recurrence in Patients Treated with Breast-Conserving Therapy

Among all in-breast tumor recurrences (IBTR) following breast-conserving therapy (BCT), some comprise metachronous new primaries (NPs) while others are true recurrences (TRs). Establishing this distinction remains a challenge. We studied 3932 women who underwent BCT for stage I-III breast cancer from 1998 to 2008. Of these, 115 (2.9%) had an IBTR. Excluding patients with inoperable/unresectable recurrences or simultaneous distant metastases, 81 patients with isolated IBTR comprised the study population. An IBTR was categorized as an NP rather than a TR if it included an in situ component. The log-rank test and Kaplan-Meier method were used to evaluate disease-free survival (DFS) and overall survival (OS), and univariate and multivariate analyses were performed using Cox proportional hazards regression models. At a median of 64.5 months from IBTR diagnosis, 28 of 81 patients had DFS events. Five-year DFS was 43.1% in the TR group (p = 0.0001) versus 80.3% in the NP group, while 5-year OS was 59.7% in the TR group versus 91.7% among those with NPs (p = 0.0011). On univariate analysis, increasing tumor size, high grade, positive margins, lymphovascular invasion, node involvement, lack of axillary surgery, chemotherapy, radiation therapy, and IBTR type (TR vs. NP) were significantly associated with worse DFS. Controlling for tumor size and margin status, TRs remained significantly associated with lower DFS (hazard ratio 3.717, 95% confidence interval 1.607-8.595, p = 0.002). The presence of an in situ component is associated with prognosis among patients with IBTR following BCT and may be useful in differentiating TRs and NPs.