Proteus syndrome (PS) is a severe, variable, and rare disorder with asymmetric and disproportionate overgrowth of body parts, cerebriform connective tissue
nevi, epidermal
nevi, dysregulated adipose tissue, and
vascular malformations. It is associated with benign and occasionally malignant
tumors. We report the first case of
ductal carcinoma in situ (
DCIS) in a 28-yr-old woman with PS who underwent a
mastectomy for asymmetric overgrowth. The cut surface of the tissue showed a discrete, white, lobulated, solid mass with multiple
cysts with occasional small polypoid nodules. Microscopically, the tissue was characterized by neoplastic and non-neoplastic changes. The former consisted of multiple
intraductal papillomas and low-grade intraductal papillary, solid, and
cribriform carcinoma. The non-neoplastic changes were characterized by
cysts of various sizes, lined by cuboidal or apocrine cells, focally with epithelial papillary proliferation; the lumens contained eosinophilic,
mucicarmine-positive, and PAS-positive material. Variable ductal proliferation and periductal, peri- and intra-lobular
fibrosis with loose fibrous connective tissue was present. The
carcinoma was positive for ER, PR, CK7, and MIB-1 (40%), and negative for p53 and CK20 staining. We conclude that
DCIS may be one of the
tumors associated with PS and that the proliferative phenotype serves as an initiator for
carcinogenesis. This case highlights the difficulty of recognizing small foci of
carcinoma in an asymmetrical overgrowth of the breast in a young woman with PS.