Encapsulated apocrine papillary carcinoma of the breast--a tumour of uncertain malignant potential: report of five cases.

Five cases of an unusual encapsulated apocrine papillary tumour are reported. All presented as cystic masses in the breast of women aged 44-84 years. Imaging studies showed a complex cyst often with one or more mural nodules. The key histological features are similar to those of classical encapsulated papillary carcinoma in that myoepithelial cells were absent within the papillary structures and at the periphery of the cyst. All were pure apocrine in type and showed variable degrees of cytological atypia and mitotic activity. All lacked evidence of malignancy in the breast tissue outside of the lesion. Sentinel lymph node biopsies performed in three of the cases were negative for metastases, and all have behaved in a benign fashion.