Cohort study of women treated with chemotherapy for breast cancer during pregnancy compared with non-pregnant breast cancer patients

Introduction: Breast cancer continues to be the most common cancer diagnosed in pregnant women. Management of breast cancer in pregnant patients requires finding a fine balance between treating the pregnant patient adequately while minimizing toxicity to the fetus. Our objective was to evaluate overall (OS) survival and disease-free survival (DFS) of women with breast cancer treated with standard chemotherapy during pregnancy compared to non-pregnant breast cancer patients. Methods: Pregnant patients treated at The University of Texas MD Anderson Cancer Center during 1989-2018 for stage I-III breast cancer were matched to non-pregnant breast cancer patients. We used coarsened exact matching (CEM) on pretreatment age category ( 35), diagnosis year ( 2004), tumor stage (I vs. II/III), HER2 status, and hormone receptor status. Next, we used propensity score matching within CEM strata to prune matches to no more than 2 per pregnant case, and CEM weights were recalculated to use in analyses. Our resulting sample included 93 of 99 eligible pregnant patients from a registry trial and 190 of 13,470 non-pregnant patients from an institutional database of breast cancer patients. We reviewed medical records to collect follow-up data and compared OS and DFS between cohorts using the Kaplan-Meier method log-rank test. The Institutional Review Board approved this study (protocol #PA 18-0038). Results: Median age at diagnosis was 33.5 (Interquartile range (IQR) 6.7) for the pregnant cohort and 33.5 (IQR 9.2) for the non-pregnant cohort. In each cohort, 7.5% had a stage I tumor, and for the pregnant vs. non-pregnant cohort, 46% vs. 60% were stage II and 46% vs. 32% were stage III. The median time to treatment start with chemotherapy from pathologic diagnosis was 35 days (IQR 32.5) for pregnant patients and 31 days (IQR 44) for non-pregnant patients. All patients in the pregnant cohort and 91% in the non-pregnant cohort received chemotherapy. For each cohort, 51% were hormone receptor positive, 22% were HER2 positive, and 41% had triple negative disease. Median follow-up for patients who were alive at the end of follow-up was 5.4 years (IQR 10.5). In univariable analyses, cohorts did not show statistically significant differences in DFS (p = 0.13) or OS (p = 0.38). For pregnant and non-pregnant cohorts respectively, 5-year DFS was 77% (95% CI 66%, 85%) and 65% (95% CI 52%, 76%), and 5-year OS was 82% (95% CI 72%, 89%) and 80% (95% CI 67%, 88%). Multivariable results will be reported. All pregnant patients had viable babies at term. Conclusion: This study suggests that patients with breast cancer during pregnancy can be treated safely with chemotherapy and have survival comparable to that of non-pregnant patients. Long term outcomes for pregnant breast cancer patients and their children exposed to chemotherapy in utero should continue. Citation Format: Oluchi Oke, Carla Warneke, Ashley Martinez, Richard Theriault, Jennifer Litton. Cohort study of women treated with chemotherapy for breast cancer during pregnancy compared with non-pregnant breast cancer patients [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P4-14-02.