Dynamics of the hazard for distant metastases after ipsilateral breast tumor recurrence according to estrogen receptor status : an analysis of 2851 patients

Background: Breast cancer (BC) patients with ipsilateral breast tumor recurrence (IBTR) are at high risk of developing distant metastases (DM). We aimed to evaluate the risk pattern of developing DM, with respect to the occurrence of IBTR, in a large series of patients homogeneously treated by conservative surgery (QUART) with a considerably long follow-up. Methods: Piecewise exponential model was used to investigate DM dynamics conditioning on known prognostic factors and IBTR occurrence as time dependent covariate. The model was extended to account for the timescale induced by IBTR, namely the time elapsed since IBTR to the endpoint. Results: Among 2851 BCE patients receiving QUART, 209 were assessable for IBTR. After a median follow-up of 129 months, 588 patients presented DM (CCI = 27.3%) as first event and 92 (CCI = 48.8%) following IBTR. Primary tumor size and nodal status confirmed their prognostic value. The hazard for DM was early and high in Estrogen Receptor (ER) negative BC patients; while it was initially low but increases during follow-up in ER positive cases. Patients experiencing IBTR showed DM dynamic similar to that following primary tumor, with a sudden increased risk within 24 months from surgery, regardless the time elapsed since QUART. Conclusion: BC patients experiencing IBTR showed a sudden and sustained risk of DM following surgery. Our findings are consistent with the hypothesis that IBTR occurrence might act as a “time resector” for risk of DM, and provide a rationale for proper surveillance guidelines and systemic therapy for optimizing BC recurrence and appropriate choice of treatment.