Abstract
Pure mucinous carcinoma is a rare special type of breast carcinoma with a 2% incidence and it is usualy asociated with a good prognosis. It must distingished from the mixed subtype of mucinos breast carcinoma, which has an invasive non-mucinous component in more than 10% of the tumor and change the favourable outcome of the first subtype. In this report we present a case of a premenopausal woman with a lump in right breast wich histopathologically proved to be a pure mucinous carcinoma associated with high grade ductal carcinoma in situ. Immunohistochemical and ancillary studies demonstrate a great heterogeneity of the neoplastic cells, with different molecular profile for each component of the tumor. The presence of ductal carcinoma in situ with a different imunophenotype from pure mucinous carcinoma rise the ipothesis of a different tumor cell biology which may change clincal evolution.