Abstract PO4-02-08: Outcomes of patients treated with chemotherapy for breast cancer during pregnancy compared with non-pregnant breast cancer patients treated with systemic therapy
Authors: Johnson Helen , Warneke Carla , Martinez Ashley , Litton Jennifer , Oke Oluchi 
Published: May 2024

Abstract
Introduction: Prior studies comparing outcomes of patients diagnosed with and treated for breast cancer during pregnancy (PrBC) with those of non-pregnant patients with breast cancer report mixed results. Data are sparse for PrBC patients treated with systemic therapy, who may be at risk for poorer outcomes owing to the need to modify regimens or delay initiation of teratogenic agents until the postpartum period. This study aims to compare survival outcomes of PrBC patients treated with chemotherapy during gestation versus matched non-pregnant breast cancer patients treated with systemic therapy.
Methods: Pregnant women with non-metastatic, non-inflammatory breast cancer treated with chemotherapy during gestation on prospective institutional protocols from 1989-2022 were identified. Two non-pregnant patients selected from a departmental database were matched to each PrBC patient using coarsened exact matching based on age at diagnosis (&lt; 30 years old, 30-35, &gt;35), year of diagnosis (&lt; 1997, 1997-2004, &gt;2004), stage at diagnosis (I, II or III), hormone receptor (HR) status, and Human epidermal growth factor receptor 2 (HER2) status. Retrospective chart review was performed to update vital status and other clinical data. Overall survival (OS) was calculated from diagnosis until last known vital status and compared using the Kaplan-Meier method and log-rank test.
Results: 167 PrBC patients were matched to 334 non-pregnant patients (Table 1). Median age at diagnosis was 33 years for both cohorts (IQR: PrBC, 6; non-pregnant 7). Other characteristics are shown in Table 1. Median time from diagnosis to initiation of chemotherapy or oncologic surgery was 25 days (IQR 27) for PrBC patients and 27 days (IQR 37) for non-pregnant patients (p=0.61). Anti-HER2 therapy was deferred to the postpartum period for PrBC patients, with median time from diagnosis to therapy initiation of 73 days (IQR 190) compared with 63 days (IQR 143) for non-pregnant patients (p=0.36). Median follow-up was 4.5 years (IQR 9.0) for PrBC patients and 5.8 years (IQR 7.5) for non-pregnant patients (p=0.27). At last follow-up, 128 PrBC patients (77%) and 222 non-pregnant patients (66%) were alive. Median OS was 24.1 years (95% CI 15.8-undefined) for PrBC patients and 14.0 years (95% CI 10.8-33.8) for non-pregnant patients. OS did not differ significantly between cohorts (p=0.12).
Conclusion: This retrospective, matched cohort study suggests that PrBC patients treated with chemotherapy during gestation have comparable OS compared with non-pregnant breast cancer patients treated with systemic therapy, despite treatment modifications and delayed initiation of teratogenic agents. This is the largest reported cohort of PrBC patients treated with a standardized chemotherapy protocol during gestation and therefore adds valuable insight into outcomes of this uncommon presentation of breast cancer. Continued study is needed to determine whether longer-term outcomes are similar, particularly for patients with triple-negative breast cancer who did not receive immunotherapy during pregnancy.
Table 1 Baseline characteristics
Citation Format: Helen Johnson, Carla Warneke, Ashley Martinez, Jennifer Litton, Oluchi Oke. Outcomes of patients treated with chemotherapy for breast cancer during pregnancy compared with non-pregnant breast cancer patients treated with systemic therapy [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-02-08.