Survival of women with pregnancy-associated breast cancer according to clinical characteristics: A propensity score matching study

In recent years, postponing childbearing has increased the prevalence of pregnancy-associated breast cancer (PABC). PABC has a poorer prognosis than breast cancer not associated with pregnancy (non-PABC) due to delayed diagnosis and aggressive subtype. Additionally, pregnancy itself predicts a poor prognosis; but, this is a subject of debate. Thus, we analyzed the effects of known prognostic factors and pregnancy on the prognosis of PABC. We retrospectively analyzed women aged 20 to 49 years who were diagnosed with breast cancer (BC) between 1989 and 2014. Patients were distributed into PABC and non-PABC groups, and 1:4 propensity score matching was performed to adjust for baseline characteristics. Primary endpoints were overall survival (OS) and BC-specific survival (BCSS). Secondary endpoint was the difference in prognosis according to BC subtype. Of the 34,970 recruited patients with BC, 410 (1.2%) had PABC. Patients with PABC were younger and tended to have triple-negative BC (TNBC) subtype than non-PABC patients. The 1640 matched non-PABC patients showed a significantly worse mean survival rate than the unmatched non-PABC patients. Patients with PABC had a significantly worse OS and BCSS than those with non-PABC. In multivariate analyses, patients with PABC of luminal B (Ki-67 ≥14.0%) and TNBC subtypes had worse OS and BCSS than patients with non-PABC. Patients with PABC had poorer prognosis than non-PABC patients after adjusting for several prognostic factors. This difference was particularly significant in patients with the luminal B and TNBC subtypes.