There are two types of ectopic breast tissue: accessory breast (polymastia) and aberrant breast tissue. Breast cancer may arise in any type of ectopic breast tissue, although rarely.A 50-year old woman had a palpable mass near an accessory nipple. Physical and X-ray examination suggested a benign tumour, but after excision and pathological examination it turned out to be breast cancer. After follow-up examination a re-excision with a sentinel node procedure was performed. There was no indication for adjuvant therapy.Due to the atypical location, the diagnosis 'breast cancer in an accessory breast' is usually made in a late stage. Due to the small amount of breast tissue, invasion of skin or underlying tissue is more common. Drainage of lymph fluids may be different as well, which has to be taken into account when performing a sentinel node procedure. Also, lymph node metastases may present in the ipsilateral mamma. These particulars should be taken into account in the treatment of cancer in ectopic breast tissue.