The breast tissue develops from the milk line from approximately 7 weeks gestation. The ducts arise from the ectodermal mammary ridge which develops into a budding stage by the 12th week. The milk line extends from the axilla to the groin and is responsible for vestigial accessory nipples. However the axilla to groin concept of the nipple line in humans has been challenged as accessory nipples are only found in the axillo-pectoral region (Mansel et al. 2009). The most common embryological vestige is accessory breast in the axilla (Fig. 1.1).

Whist developing in utero, the breast epithelium and stroma are under the influence of growth factors and placental hormones, which include prolactin, oestrogen and progesterone (Forsyth 1991). Falling of maternal oestrogens in the neonatal period stimulates the production of prolactin which induces secretory changes in the breast. This results in unilateral or bilateral enlargement of the breasts which may be associated with secretion of ‘witches milk’. At birth there is no difference between the male and female breast tissue, but the presence of testosterone leads to the involution of the male breast.

Thelarche, which commences between 10 and 12 years, heralds the rapid growth of the breast at the onset of puberty. The pituitary hormones follicle-stimulating hormone (FSH) and luteinising hormone (LH) stimulate the production of oestrogen and progesterone, resulting in the enlargement of the areola and the nipple, development of the lobules and associated acini and increase in intralobular stroma and fat. Abnormal secretion of the hormones can result in premature thelarche which is characterised by unilateral or bilateral development of breast tissue before puberty. Erroneous interpretation of breast enlargement in premature thelarche as pathological can lead to surgical excision rendering the child amastic. The breast tissue in premature thelarche regresses with time.