Breast aplasia may be congenital or may occur after surgery. A known genetic aplasia is the Poland syndrome: usually the breast and the pectoral muscles are missing (◘ Figs. 15.1, 15.2, and 15.3). In rare cases, changes in the arm and hand (symbrachy-phalangia) may occur. Poland syndrome is more frequently localized on the right side and more frequently in men than in women. Exact data is missing. In Poland syndrome, not only the missing breast but often also the missing contour of the pectoralis muscles, i.e. the anterior border of the axilla, is disturbing for the patients. The extent can vary.