Karyotypic and histopathologic findings in an accessory breast.

Accessory breasts are a clearly hereditary anomaly. They enlarge during pregnancy and lactation as a consequence of high blood levels of estrogen and prolactin, and are subject to all the diseases that occur in normal breasts. Cytogenetic analysis was performed on one accessory breast. The monossomy of chromosome 16 was the main alteration found in this material. Nonscheduled cell proliferations may produce chromosome alterations, most of them with no clinical meaning. When relevant genes are altered, major proliferations or progression to malignancy may occur.