A population-based series of 122 patients with pregnancy-associated breast carcinomas was histologically revised and the relationship between hormone receptors, c-erbB-2, BRCA1, p27, cyclin E, and cyclin D1 was studied. The 5-year overall survival was 41%; 70% had tumor size >20 mm; 72% had metastasized to regional lymph nodes; 95% were histologic grade II or III; 66% and 75% were negative for estrogen and progesterone receptor, respectively; and c-erbB-2 expression was high (44%). BRCA1 expression was reduced in 33% of the cases. The expression of p27, cyclin D1, and cyclin E was low, 11%, 9%, and 16%, respectively. Cyclin D1 was positively associated with the hormone receptors (p< or =0.01). In multivariate analysis, lymph node status, progesterone receptor, and c-erbB-2 were significant prognostic factors. In subdividing the group according to lymph node status, c-erbB-2 and progesterone receptor retained a prognostic significance in the node positive group only. In conclusion, pregnancy-associated breast carcinomas are aggressive tumors, with low expression of hormone receptors, BRCA1, p27, and cyclin E and D1, and high expression of c-erbB-2.