Abstract PS13-01: Worse Prognosis for Breast Cancer in the Second and Third Trimesters and Shortly Postpartum:An Update of the Dutch Pregnancy-Associated Breast Cancer Cohort
Authors: Bakhuis Carsten , Van Dooijeweert Carmen , Suelmann Britt , Verloop Janneke , Westenend Pieter , Linn Sabine , Van Diest Paul , Van der Wall Elsken 
Published: May 2024

Abstract
Rationale:
Pregnancy-Associated Breast Cancer (PABC), often defined as breast cancer during pregnancy (PrBC) or in the first year postpartum (PPBC), is known for its aggressive histopathology and higher stage at diagnosis. In a previous study of the nationwide Dutch PABC Cohort, we observed an impaired survival for patients diagnosed in the second and third trimester of pregnancy. However, the etiology of these differences, and how this relates to the patients diagnosed with breast cancer in the postpartum period (PPBC) or after an abortion (AABC), remains to be elucidated. While we are exploring the etiologic hypotheses, we updated and expanded our database to compare these specific PABC subgroups.
Methods:
All pathology reports of invasive breast carcinoma between January 1st 1988 and July 1st 2022 were screened for pregnancy-related keywords to find all patients diagnosed with PrBC, PPBC or AABC within one year after childbirth or an interrupted pregnancy (induced abortion or miscarriage before a gestational age of 24 weeks). A local patient series provided 22 additional cases. Pregnant patients were subdivided by gestational trimester at time of diagnosis. The different PrBC, PPBC and AABC subgroups were compared by histopathology, clinical characteristics and outcome.
Results:
787 patients were included, of whom 60% were pregnant during their diagnosis. Median age at diagnosis was 34 years. In line with our previous findings, a large majority (68%) of patients had a Bloom & Richardson (B&R) grade III tumor and 37% of tumors were triple negative. Moreover, over a third of patients presented with lymph node metastases (38%). We observed two distinct groups based on histopathology and prognosis: group A, consisting of three patient groups: (I) patients diagnosed in the first trimester of pregnancy, (II) patients diagnosed between 6-12 months postpartum, and (III) patients diagnosed after an abortion, and group B, consisting of two patient groups, (I) patients diagnosed in the second or third trimester of pregnancy or (II) within 6 months after childbirth. Compared to group A, patients in group B more often had B&R grade III tumors: (73% vs. 60%, p=0.002) and more frequently had triple negative tumors (43% vs. 28% in group A, p&lt; 0,001). Survival was significantly worse for patients in group B (5-year OS 67,3% versus 88.2%, p&lt; 0.001). In a multivariable analysis, corrected for grade, type of surgery and overall stage, these differences upheld with an HR of 1.515 (95% CI 1,012 – 2,268).
Conclusions:
With this extensive update of our nationwide Dutch PABC cohort, we show that especially PrBC patients diagnosed in the second and third trimesters and PPBC patients within six months after childbirth exhibit unfavorable tumor characteristics, with an associated worse prognosis. This highlights the need for in-depth analyses in these specific groups of PABC patients to elucidate the etiologic mechanisms involved.
Citation Format: Carsten Bakhuis, Carmen Van Dooijeweert, Britt Suelmann, Janneke Verloop, Pieter Westenend, Sabine Linn, Paul Van Diest, Elsken Van der Wall. Worse Prognosis for Breast Cancer in the Second and Third Trimesters and Shortly Postpartum:An Update of the Dutch Pregnancy-Associated Breast Cancer Cohort [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 PS13-01.