Fibroadenoma and cystosarcoma phyllodes of the male breast.

Five biphasic tumors, four fibroadenomas and one cystosarcoma phyllodes, are reported in the male breast. Gynecomastia and lobular development were present in all five cases. The rarity of fibroadenoma and cystosarcoma phyllodes in men is attributed to the absence of lobules in the normal male breast. We propose that lobular development precedes biphasic tumors in the male breast. The development of lobules apparently requires a certain length and/or intensity of endogenous or exogenous estrogenic stimulation not frequently attained at the levels that commonly induce gynecomastia.