The development of the supernumerary breast (polymastia or hypermastia) and its modality constitutes an interesting chapter in clinical observation. The subject is of clinical interest because of the differential diagnosis of supernumerary breasts and lipomas and other benign tumors and because of the discomfort caused by the swelling of aberrant breast tissue during pregnancy and childbirth. It is also important to establish that there is no evidence that carcinoma develops more frequently in these formations than in normal breasts.
There are in the literature almost six hundred references to congenital anomalies of the breast. In the human being the supernumerary organs develop either in the milk line or in locations that are atypical for human beings but normal for other mammals. A short sketch of the embryology and comparative anatomy may therefore be of interest, in addition to a description of some new cases and a summary of cases collected
de CHOLNOKY T. SUPERNUMERARY BREAST. Arch Surg. 1939;39(6):926-941. doi:10.1001/archsurg.1939.01200180027002