Abstract:

A 22-year-old patient was admitted to the hospital with a solitary, gradually growing and painless mass in the left shoulder for 2 years. Physical examination revealed no abnormality except for the skin lesion. Skin examination showed an elevated lesion measuring about 3.5 cm × 2.0 cm × 1.5 cm with smooth surface and normal color, which was located in the subcutaeous tissue, indurated and movable. Resection of the tumor was performed under local anesthesia. On visual observation during operation, the tumor was sited in the subcutaneous fat tissue, nodular-like and surrounded locally by fibrous pseudocapsules with a grey incisal surface and mild texture. Microscopically, the tumor was extremely similar to breast fibroadenoma with multiple lobuli, and each of the lobuli was composed of tubiform structures, basal cell-like epithelial cell trabs and fibromyxoid stroma abundant in fibroblast-like spindle cells. No hair bulb or primitive dermal papillae were observed in the lobuli, which were separated by compact collagen fibers infiltrated by a few scattered inflammatory cells. Fibromyxoid stroma was surrounded by basal cell-like epithelial cell strabs in most lobuli, and some tubiform structures were filled with a little thin lightly eosinophilic material in a concentric arrangement. Immunohistochemistry showed that intralobular epithelial cells were strongly positive for cytokeratin 5/6, but negative for CAM5.2 or carcinoembryonic antigen （CEA）. In addition, the lightly eosinophilic material in lumens was negative for periodic acid-Schiff （PAS） staining. These results suggested that the tubiform structures were immature follicles, but not sweat ducts. The patient was diagnosed with nodular fibrofolliculoma （NFF） based on the clinical manifestations, morphological features, immunohistochemical and PAS staining results. No relapse was observed in more than 3 months of postoperative follow-up. As a benign trichogenic adnexal neoplasm with unique clinicopathological manifestations, NFF may be a new entity of cutaneous adnexal neoplasm.

Key words: entity