Prognosis of 368 women with primary breast cancer diagnosed during pregnancy: results from an international collaborative trial

Objective: We aimed to add to the limited outcome data on breast cancer during pregnancy (BCP), and compared disease-free survival (DFS), and overall survival (OS) between patients with BCP and breast cancer not diagnosed during pregnancy, adjusted for known prognostic factors. Methods: We analyzed a pro- and retrospectively compiled multi-centric registry of BCP patients (www.cancerinpregnancy.org and GBG/BIG 0203). Outcome was compared to a control group of patients who did not have associated pregnancies. The main analysis is a Cox proportional hazards regression of disease free survival (DFS) and overall survival (OS) on exposure (pregnant or not). The analysis was weighted by propensity score matching to correct for any bias that may have been associated with differences in baseline characteristics, with the following set of covariates: age, stage, grade, hormone receptor status, HER2 status, histology, type of chemotherapy and trastuzumab. Sensitivity analysis was also performed on age only, and also on chemotherapy only. Results: From April 2003-December 2011, 447 women with BCP were registered, 368 women with BCP were eligible for this analysis. The control group consisited of 2739 women (ratio 1:7.44).