Prognosis of pregnancy-associated breast cancer: inferior outcome in patients diagnosed during second and third gestational trimesters and lactation

Purpose: Pregnancy-associated breast cancer, although most commonly defined as breast cancer diagnosed during pregnancy or ≤1 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, time after delivery and the postpartum period is therefore warranted. Methods: Patients with breast cancer diagnosed during pregnancy or ≤6 months postdelivery were included, and subdivided according to gestational trimester, and postpartum patients according to lactational status. Subgroups were compared to matched non-PABC patients, to investigate the influence of pregnancy and lactation on clinical course and outcome. Results: Overall, 662 PABC patients were included (median age 34 years, median follow-up 6.5 years). PABC patients showed an advanced stage at diagnosis and an inferior 5-years-OS (75.4% vs. 83.2%, p = 0.000) compared to 1392 matched non-PABC patients. In subgroup analysis, first trimester PABC patients 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). Conclusion: In this large (uniquely specified) PABC cohort, an inferior outcome was found for patients diagnosed within the second and third gestational trimesters and during lactation. These findings indicate that PABC is clinically a heterogeneous group of breast cancer patients that should be redefined based on trimester of diagnosis and lactational status.