Abstract: 【Abstract】 A 28-year-old male patient presented with a 4-year history of a solitary brown mass, and a 1-year history of multiple small papules on the left chest. Skin examination showed a quasi-round brown firm mass measuring about 1.2 cm × 1.1 cm × 1.0 cm in size on the left chest, and several brown papules with a diameter of 3 - 5 mm on the right side of the mass; no enlarged lymph nodes were detected in the left axilla on palpation. The mass and papules were completely removed, and histopathological examination showed clustered nevus cells in the superficial dermis of the mass and small papules, and the diagnosis of intradermal nevus was considered. There was a desmoplastic nodule in the mass, nevus cells were scattered among the fibers in the nodule, and giant nevus cells were also observed; the nevus cells in the nodule were relatively larger, epithelioid or spindle-shaped with round or spindle-shaped nuclei, obvious nucleoli, and rare mitotic figures. Immunohistochemical study showed that the nevus cells in both the intradermal nevus and proliferative nodule were positive for S100; the nevus cells in the superficial dermis of the intradermal nevus were positive for Melan-A and HMB45, while the nevus cells in the proliferative nodule were negative for Melan-A and HMB45; both the intradermal nevus and proliferative nodule tissues showed a Ki-67 index of 1%, positive staining for CD34, but negative staining for P16 and P63. Finally, the patient was diagnosed with intradermal nevus associated with desmoplastic nodule.

Key words: Nevus, pigmented, Connective tissue, Nodule