The concomitant occurrence of breast cancer and pregnancy remains a challenging clinical situation combining ethical and medical problems. There are few prospective data on pregnancy-associated breast cancer (PABC) whose incidence continuously increases.Forty patients with PABC were compared with 61 non-pregnant, age-matched patients with infiltrative breast carcinomas (BC) diagnosed and followed since 1982.Although PABC and BC tumor size, grade and type, and lymphovascular and lymphnode invasion were similar, the BC cases showed better overall--(p=0.0001) and disease-free (p-0.015) survival. Moreover, the outcome of pregnant patients was worse than post-partum patients (p=0.017). Importantly, the number of PABC patients receiving hormonotherapy was lower than the BC patients (p<0.0004), due to lower estrogen receptor (ER) (p=0.038) and progesterone receptor (PR) (p=0.008) immunohisto-chemical (IH) levels. Retrospective estrogen-regulated pS2/trefoil factor 1 (pS2/TFF1) immunohistochemitry showed no difference between PABC and BC. All the children delivered were healthy.Pregnancy and the post-partum period increase breast cancer aggressiveness, pregnancy being the most detrimental. PABC hormone-dependence is under-estimated using ER and PR, and pS2/TFF1 might help in its determination. Appropriate treatment does not impair child outcome.