Tracing differences between male and female breast cancer: both diseases own a different biology.

Aims: Male breast cancer (MBC) is a rare and poorly characterized disease. In the present study we used a novel biomathematical model to further characterize MBC and to identify differences between male and female breast cancer (FBC). Methods and results: A total of 134 cases of MBC were stained immunohistochemically for 13 key oncoproteins, and staining percentages were used in a mathematical model to identify dependency patterns between these proteins. The results were compared with a large group of FBC (n = 728). MBC and FBC clearly differed on the molecular level. In detail, the results suggest a different role for progesterone receptor (PR) compared to oestrogen receptor (ER) in MBC, while in FBC ER and PR show a similar pattern. In addition, Androgen receptor (AR) seems to be a more powerful effector in MBC. Grades 1 and 2 tumours were clearly separated from grade 3 tumours, and luminal types A and B tumours also showed a different pattern. Conclusions: Defined morphological and molecular phenotypes can be identified in MBC, but these seem to be the result of different molecular mechanisms and perhaps multiple genetic pathways, as characterized previously in FBC, emphasizing the rising concept that MBC and FBC should be regarded as different and unique diseases.