Effects of clinical heterogeneity on Pregnancy-Associated Breast Cancer survival: a systematic review with meta-analysis

Pregnancy-associated breast cancer is defined as a diagnosis of breast cancer during pregnancy or within 1 year of childbirth. Current evidence shows that Pregnancy-associated breast cancer is associated with poor prognosis; however, no systematic review has summarized and explored how baseline characteristics could impact survival. We aimed to explore the impact of breast cancer characteristics on death and disease relapse. A systematic review with meta-analyses was conducted by searching articles in the main databases (Medline, Embase, and Cochrane) and congress abstracts. Summarized death and disease-free survival hazard ratios were recalculated, and all meta-analyses used a random-effects model. Heterogeneity was reported using the I2 method. A total of 7143 studies were identified and only 30 studies were included. Pregnancy-associated breast cancer is associated with a 96% (HR 1.96; 95%CI 1.58­2.35) higher risk of death and 82% (HR 1.82; 95%CI 1.45­2.20) risk of death or disease relapse in comparison to a population of non-pregnancy-associated breast cancer or nulliparous breast cancer. Through sensitivity analyses, we identified that clinical outcomes were impacted, possibly due to Ki-67 levels, poorly differentiated tumors, and triple-negative breast cancer frequency in the study. As relevant sources of inconsistencies, such clinical cancer-related characteristics should be better investigated as potential confounders for upcoming Pregnancy-associated breast cancer therapeutic strategies.