Forty-two patients with clinical stage IIIA or IIIB breast cancer were treated with neoadjuvant chemotherapy followed by mastectomy and radiotherapy. The median follow-up was 32 months (range 10-72 months) and the median time to progression was 17 months (range 10-30 months). A multivariate analysis showed that a longer disease-free survival (DFS) was related to more chemotherapy cycles given (P = 0.003), a better pathological response to chemotherapy (P = 0.04) and fewer positive axillary lymph nodes (P = 0.05). A better overall survival (OS) was related to more chemotherapy cycles given (P = 0.03) and better pathological response to chemotherapy (P = 0.04). In patients with residual tumour after neoadjuvant chemotherapy, high levels of staining for Ki-67 was correlated with a worse DFS (P = 0.008). Other biological characteristics, including oestrogen receptor status, microvessel density (CD31 staining), P-glycoprotein (P-gp) staining and nuclear accumulation of p53, were not independent prognostic factors for either DFS or OS. If both P-gp and p53 were expressed, DFS and OS were worse in the uni- and multivariate analysis. The preliminary results of this phase II study suggest that coexpression of P-gp/p53 and a high level of staining for Ki-67 after chemotherapy are associated with a worse prognosis, and that prolonged neoadjuvant chemotherapy and the attainment of a pathological complete remission are important factors in determining outcome for patients with this disease.