Long-Term Breast Cancer Outcomes of Pregnancy-Associated Breast Cancer (PABC) in a Prospective Cohort

SIMPLE SUMMARY: This study explored the characteristics, treatment, and survival outcomes of patients with pregnancy-associated breast cancer (PABC) in Korea. All patients of this study received standard treatments according to the National Comprehensive Cancer Network guideline. Compared to the non-PABC group, the PABC group had a lower percentage of hormone receptor positivity, increased HER2 overexpression, and higher Ki-67 levels. No maternal complications were observed in patients with PABC. In addition, the 5-year disease-free survival and overall survival rates were significantly poorer in the PABC group than in the non-PABC group. After adjusting for tumor characteristics, PABC was still associated with poor prognosis. This is the first report of the PABC population from a prospective cohort. Exploration to elucidate biologic relevance will follow. ABSTRACT: Background: Given that peak age of breast cancer (BC) is younger in Asians than in Western populations, relatively higher prevalence of pregnancy-associated breast cancer (PABC) has been reported. This study aimed to analyze the characteristics and clinical outcomes of PABC in Korea. Methods: We defined PABC as BC diagnosed during pregnancy or in the first postpartum year. We compared the clinicopathological characteristics and BC outcomes between patients with PABC and non-PABC patients in the prospective YBC cohort from Samsung Medical Center. Results: In total, 1492 patients were initially enrolled, and 1364 patients were included, of which 93 had PABC (6.8%). The median age of patients with PABC was 34 years. Hormone receptor expression was lower (64.6% vs 74.6%) and frequency of HER2 overexpression was higher (26.9% vs 17.6%) in patients with PABC than in non-PABC patients. The 5-year overall survival (OS) rates were 83.2% and 93.4% in patients with PABC and non-PABC patients, respectively (p < 0.001). The 5-year disease-free survival (DFS) rates were 72.2% and 83.8% in PABC and non-PABC patients. Conclusion: Compared to non-PABC patients, patients with PABC had poorer OS and DFS in this prospective cohort. Exploratory biomarker analysis for PABC is warranted.