Abstract P3-12-06: Prognosis of pregnancy-associated breast cancer: Inferior outcome in patients diagnosed during second and third gestational trimesters and lactation (2022)

Abstract BACKGROUND Pregnancy-associated breast cancer (PABC), although most commonly defined as breast cancer diagnosed during pregnancy or within one year following delivery, knows a variety of definitions, likely related to the diversity of reported clinicopathological features and prognosis. More insight into the different breast cancer subgroups during pregnancy, the time after delivery and the postpartum period is therefore warranted. METHODS Patients with breast cancer diagnosed during pregnancy or within six months after delivery between January 1, 1988 and July 1, 2019, were included. Pregnant patients were subdivided according to gestational trimester, and postpartum patients according to lactational status. To investigate the influence of pregnancy and lactation on the histopathologic profile, these subgroups were compared to non-PABC patients matched for age at diagnosis, year at diagnosis, grade and ER status. Pearson Chi-square tests were used to compare clinicopathologic characteristics, while Kaplan-Meier/logrank/Cox regression methods were used to perform overall survival (OS) analysis. RESULTS Overall, 662 PABC patients were included, of which 73.6% were diagnosed during pregnancy. Median age at diagnosis was 34 years, with a median follow-up of 6.5 years. Overall, PABC patients as a group showed an advanced stage at diagnosis and an inferior OS at 5-years (75.4% vs. 83.2%, p = 0.000) compared to 1,392 non-PABC patients. In subgroup analysis, PABC patients within their first trimester showed a significantly lower tumor size and stage as compared to other trimesters. Patients diagnosed during the first trimester and postpartum non-lactating patients had a relatively good OS (81.3% and 77.9%, respectively) versus patients diagnosed during the second and third trimesters and during lactation (OS 60.0%, 64.9% and 65.6%, respectively, p = 0.003). In multivariate Cox regression, trimester of diagnosis, year of diagnosis, PR status, stage at diagnosis and surgery-or-not were significant contributors to OS. CONCLUSION In this large PABC cohort, uniquely specified by gestational trimester, an inferior outcome was found for patients diagnosed within the second and third gestational trimesters and during postpartum lactation, compared to first trimester and non-lactating postpartum patients. These findings indicate that PABC is clinically a heterogeneous group of breast cancer patients that should be redefined based on trimester of diagnosis and postpartum lactational status. Citation Format: Britt BM Suelmann, Carsten FJ Bakhuis, Carmen van Dooijeweert, Janneke Verloop, Ronald P Zweemer, Sabine C Linn, Elsken van der Wall, Paul J van Diest. Prognosis of pregnancy-associated breast cancer: Inferior outcome in patients diagnosed during second and third gestational trimesters and lactation [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P3-12-06.