The Impact Of Pregnancy-Associated Breast Cancer (Pabc) According To Immunohistochemical (Ihc) Subtype: A Matched Case-Control Study

PABC diagnosed during gestation or 12 months after delivery poses a challenge to diagnosis and treatment. Its prognosis compared to non-PABC remains controversial and data based on IHC classification are scarce. The aim of this study matched by clinical stage and IHC was to assess if pregnancy and early postpartum influence survival by subtype. A single-center medical record review was performed to identify PABC patients diagnosed with stage I-III disease from January 2007 through June 2018. Controls were matched to PABC cases in a 2:1 ratio by stage, IHC subtype, age at diagnosis (± 3) and year of diagnosis (± 2). Disease-free survival (DFS) and overall survival (OS) were estimated with the Kaplan-Meier method and compared with the log-rank test. Multivariate analysis was used to assess the independent impact of PABC on outcome. 99 PABC cases and 198 controls were included. Median age was 36 years (21-48). Subtype distribution was: 43% hormone receptor (HR)-positive/HER2-negative disease, 34% triple negative (TN) and 23% HER2-positive tumours. 4-year DFS was inferior in the PABC cohort compared to controls (62% vs 80%, p=<0.001), particularly in HR-positive/HER2-negative (64% vs 78%, p=0.032) and HER2-positive disease (48% vs 80%, p=0.005), with a nonsignificant similar trend in TN cases (71% vs 84%, p=0.273). On multivariate analysis, PABC diagnosis had an independent impact on 4-year DFS of HR-positive/HER2-negative (HR: 1.95, 95%CI: 1.02–3.73) and HER2-positive patients (HR: 3.01, 95%CI: 1.31–6.91). At a median follow-up of 67.7 months for PABC and 73.4 months for non-PABC patients, OS was similar between groups. 4-year OS was 89% in cases vs 92% in controls (p=0.565) with no differences by subtype. PABC diagnosis may influence progression particularly in HR-positive/HER2-negative and HER2-positive tumours. Further research focused on these subtypes is warranted to characterize if the increased recurrence risk is a result of the tumour biology interaction with the hormonal milieu observed during pregnancy and the microenvironment of the involuting postpartum breast, or an effect of the response to treatment due to PABC status.