Megalomastia: histological, histochemical and immunohistochemical study.

Megalomastia is a rare entity characterized by an uncommon enlargement of both breasts. Unilateral megalomastia is extremely rare. The purpose of this study was to collect information concerning the history of patients with this condition and to investigate its histology in order to outline the profile of this peculiar entity. Fifty cases of megalomastia were studied. In 41 data concerning the history of the patients was complete; there were 32 juvenile, 7 gravid and 2 adult type cases. All three unilateral megalomastias were in the juvenile group. A family history of megalomastia was frequently present; gravid megalomastia was more closely connected with a maternal familial history. A case of simultaneous megalomastia in monozygotic twins is included. The final size achieved by the breasts was independent of the type of megalomastia, the rapidity of breast development and the body weight of the patients. It was greater in breasts containing abundant adipose tissue and less in fibrous breasts. In all cases of megalomastia associated with pregnancy the breasts had lost the ability to produce milk. The main histological feature in all cases was severe damage and destruction of the lobular units associated with extensive fibrosis. In some breasts of all three types of megalomastia ramified new ducts named "juvenile units" had developed and had proceeded to atrophy. Immunohistochemistry revealed that the epithelium of these units was negative for oestrogen and positive to progesterone receptors. A biphasic pathological appearance, consisting of atrophic lobular units and "juvenile units", is diagnostic of megalomastia.