Characteristics, treatment trends, and long-term outcomes of Japanese patients with pregnancy-associated breast cancer (PABC)

Purpose To clarify the characteristics, treatment trends, and long-term outcomes of patients with pregnancy-associated breast cancer (PABC). Methods PABC includes breast cancer diagnosed during pregnancy (PBC) and breast cancer diagnosed within 1 year after childbirth or during lactation (LBC). We compared clinical characteristics of 126 patients with LBC and 49 patients with PBC who underwent surgery at our hospital from 1946 to 2018. Survival was compared between patients with LBC and those with PBC in terms of breast cancer-specific disease-free survival (BC-DFS) and overall survival (OS). Results Patients with LBC were more likely to have family history, lymph node metastasis, lymphatic invasion, and to receive chemotherapy than patients with PBC. Patients with LBC showed poorer BS-DFS and OS than patients with PBC. Among patients with LBC, those treated after 2005 were older at surgery, had a smaller tumor size, received more systemic therapy, and had a more favorable prognosis than patients treated before 2004. Family history, breast cancer within 1 year after childbirth, and surgery before 2004 as well as cStage, lymph node metastasis, and lymphatic invasion were significantly associated with poor prognosis in patients with LBC. In the multivariate analysis for BC-DFS and OS among patients with PABC, LBC vs PBC did not remain as an independent prognostic factor while cStage remained. Conclusion Patients with LBC had a poorer prognosis than those with PBC, most likely due to disease progression rather than biological characteristics. Early detection and optimization of systemic treatments are critical for improving the outcomes of patients with LBC.