Biopsies obtained from 74 Tunisian women with breast cancer (33 cases), benign breast disease (17 cases), and cervical cancer (24 cases) were assayed for the presence of an antigen cross-reacting with gp52 of the mouse mammary tumor virus (MMTV) in order to determine the frequency and possible prognostic significance of this antigen in a form of rapidly progressing breast cancer designated poussée évolutive or PEV. Antigen was detected in 23/33 breast carcinomas (70%) but in none of the 41 control specimens. An evaluation of reactivity according to tumor aggressiveness and survival could be performed in retrospect on 29 of the breast cancer patients with a follow-up of up to 11 years. The frequency of gp52-related antigen was similar in the patients with the most aggressive form of PEV with inflammatory signs (8/12 or 67% positive) and those breast cancer patients without PEV (12/17 or 71% positive). Within each of the two groups, PEV+ and PEV 0, no correlation was observed between the presence or absence of antigen and the disease-free interval or survival. We conclude that the identification of gp52-related antigens in the breast cancer biopsies from North African women has implications different from those observed in other populations. While thus far not indicative of disease aggressiveness and prognosis, the higher frequency of detectable antigen in comparison to biopsies obtained from patients born in the United States and Europe may have relevance to the etiology and pathogenesis of the disease.