Atypical ductal hyperplasia and ductal carcinoma in situ of the breast associated with perineural invasion

Perineural invasion is a histologic feature usually diagnostic of invasion in malignancies. In the breast, however, it has been associated with benign lesions such as sclerosing adenosis (SA), complex sclerosing lesion/radial scar (CSL/RS), and ductal carcinoma in situ (DCIS). This article describes perineural invasion associated with atypical ductal hyperplasia (ADH), flo rid hyperplasia without atypia (FH), and DCIS. All cases with a diagnosis o f perineural invasion were selected from a series of 10,000 breast consult cases. Invasive mammary carcinomas were excluded. Fourteen cases of perineu ral invasion were found and associated with the following diagnoses: ADH (5 ), DCIS (3), FH (5), and ductal adenoma (1). Nine cases developed in CSL/RS , 4 cases in SA, and 1 case in a previous biopsy site of ductal adenoma; le sions were all less than 3 mm. The glands involving nerves showed cytologic and architectural features of the adjacent ADH, DCIS, and FH. Immunostaini ng for protein gene product (PGP) 9.5 marked nerves, and smooth muscle acti n antibody highlighted the myoepithelial cells around glands. Perineural in vasion seen in association with DCIS and ADH, in a background of CSL/RS and SA, may pose difficulty in diagnosis, especially in small biopsy specimens . It should be assessed with care to avoid misinterpretation as invasive ma mmary carcinoma. HUM PATHOL 32:785-790. (C) 2001 by W.B. Saunders Company.