Outcome of breast cancer patients treated with chemotherapy during pregnancy compared with non-pregnant controls.

Abstract

515 Background: Overall a diagnosis of breast cancer during pregnancy (BCP) appears not to impact maternal prognosis if standard treatment is offered. However, caution is warranted as gestational changes in pharmacokinetics with respect to the distribution, metabolism and excretion of drugs may lead to reduced chemotherapy concentration in pregnant patients. This cohort study was designed to focus on the maternal prognosis of BCP patients that receive chemotherapy during pregnancy. Methods: The outcome of BCP patients treated with chemotherapy during pregnancy was compared to non-pregnant breast cancer patients treated with chemotherapy, diagnosed after 2000, excluding postpartum diagnosis and with an age limit of 45 years. The data was registered by two multicentric registries (the International Network of Cancer, Infertility and Pregnancy and the German Breast Cancer Group) that collect both retro-and prospectively breast cancer data. Cox proportional hazards regression was used to compare disease-free (DFS) and overall survival (OS) between both groups, adjusting for age, stage, grade, hormone receptor status, human epidermal growth factor 2 status and histology, weighted by propensity scoring in order to account for the differences in baseline characteristics between pregnant patients and controls. Results: In total, 662 pregnant and 2081 non-pregnant patients, were eligible for analysis. Median age at diagnosis was 34 (range 22-47) years for pregnant and 38 (range 19-45) years for non-pregnant patients. Pregnant patients were more likely to have stage II breast cancer (60.1% vs 56.1%, p = 0.035), grade 3 tumors (74.0% vs 62.2%, p < 0.001), hormone receptor-negative tumors (48.4% vs 34.0%, p < 0.001) or triple-negative breast cancer (38.9% vs 26.9%, p < 0.001). Median follow-up was 66 months. DFS and OS were comparable for pregnant and non-pregnant patients (DFS: HR 1.02, 95%CI 0.82-1.27, p = 0.83; OS: HR 1.08, 95% CI 0.81-1.45, p = 0.59). A subgroup analysis of 339 women that received more than 60% of chemotherapy during pregnancy (cut-off at median) revealed a comparable survival compared to non-pregnant women (DFS: HR 0.81, 95%CI 0.62-1.06, p = 0.13; OS: HR 0.85 95% CI 0.58-1.23, p = 0.39). Conclusions: Pregnancy-induced alternations in chemotherapy concentration do not seem to affect maternal prognosis in breast cancer patients. These results support initiation of chemotherapy for BCP where indicated for oncological reasons.