144 A Comparative Analysis of Pregnancy-Related Breast Cancer Outcomes Versus Non-Pregnant Breast Cancer Patients—A TriNetX Real-World Analysis

Background

Breast cancer diagnosed during or following pregnancy presents unique clinical and therapeutic challenges, with limited large-scale data describing maternal and oncologic outcomes. We leveraged the TriNetX global federated research network to evaluate pregnancy-related outcomes among women with breast cancer and to compare oncologic outcomes between pregnant and nonpregnant patients with breast cancer.

Materials and Methods

Using TriNetX data from 114 health care organizations, we identified adult women (≥18 years) with pregnancy-associated breast cancer (PABC; n = 10,579). Pregnancy-specific outcomes—preterm labor, preeclampsia/eclampsia, and spontaneous abortion—were assessed over a 3-year follow-up beginning 1 day after index pregnancy diagnosis. A separate propensity score–matched comparative analysis evaluated oncologic outcomes in patients with PABC vs nonpregnant breast cancer controls (n = 8879 per cohort after matching). Outcomes included mortality, chemotherapy, radiation therapy, and surgical intervention within 365 days of index event. Kaplan-Meier survival analyses and measures of association were performed.

Results

Among patients with PABC, pregnancy-related complications were uncommon: Preterm labor occurred in 0.1%, preeclampsia/eclampsia in 0.4%, and spontaneous abortion in 0.5%, with greater than 99% survival free of each outcome at 3 years. In the matched comparative analysis, patients with PABC demonstrated significantly lower 1-year mortality compared with controls (0.2% vs 1.7%; risk ratio [RR], 0.10; P <.001), with higher overall survival (99.83% vs 97.94%). Patients with PABC were also significantly less likely to receive chemotherapy (4.1% vs 31.1%; RR, 0.13), radiation (1.0% vs 13.0%; RR, 0.07), or breast surgery (1.2% vs 19.8%; RR, 0.06) within 1 year (all P <.001). HRs from survival analyses consistently favored the PABC cohort across all oncologic end points.

Conclusions

In this large real-world analysis, PABC was associated with low rates of adverse pregnancy outcomes and significantly improved short-term survival compared with nonpregnant patients with breast cancer, despite lower utilization of standard oncologic therapies. These findings highlight the need for further investigation into biological, diagnostic, and treatment-related factors influencing outcomes in PABC and support the development of pregnancy-specific breast cancer management strategies.