We present a case of 44-year old women with two primary carcinomas diagnosed in one breast. The carcinomas were invasive mixed ductal-lobular and lobular invasive carcinoma. This specific case was difficult to treat because these carcinomas are differentially susceptible to hormonal treatment. We refrained from making therapeutic decisions based solely on characteristics of the first primary would be improper because important therapeutic option (hormonal treatment) would not be used to treat the other primary. Therefore, the treatment would have been suboptimal. In our opinion, this case supports the close examination of biological characteristics of each carcinoma focus, especially if greater than one cancer focus with different morphology exists in the breast tissue.