A 33-year-old African-American woman with a severe manifestation of Poland syndrome developed breast cancer in the ipsilateral breast. She had a severely hypoplastic upper extremity, including symbrachydactyly, and a hypoplastic forearm and upper arm. In addition, she lacked the sternal origin of the pectoralis muscle. She had a very small nipple-areola complex and no axillary hair. This is the first case report of breast cancer developing in the ipsilateral breast of a patient with Poland syndrome.