Gynecomastia has been variously defined as ' "mammary feminism," "an affection of the male breast in which the gland tends to assume the size, shape, and sometimes the functions of the female breast" or simply as a "hypertrophy of the male breast." Karsner,1 in an excellent anatomical study of 280 male breasts which had been removed in treatment of this phenomenon, defined gynecomastia as "an enlargment of the mammary gland or glands of the male due to proliferation of connective tissue, dense in the general stroma and often loosely arranged in periductal regions together with variable degrees of multiplication, elongation or branching of ducts or all three without formation of true acini, accompanied by periductal or more widespread infiltration of lymphocytes, plasma cells, large mononuclear cells, and occasionally eosinophils or neutrophilic polymorphonuclear or both."
This interesting phenomenon of enlarged male breasts has been observed in association with a great variety
Rawson RW. GYNECOMASTIA IN ADOLESCENTS. JAMA. 1961;178(5):500-502. doi:10.1001/jama.1961.03040440052011