Clear cell fibrous papule with NKI/C3 expression: clinical and histologic features in six cases.

Fibrous papule of the nose is a common benign lesion of dermal fibroblast lineage. Two unusual variants have been described, namely, fibrous papule with granular cells and fibrous papule with clear fibrocytes. We report a second case series (six cases) of clear cell fibrous papule to add to the first series of 9 cases. Clinical and histologic features in our cases are similar to those in the first series. All of our specimens were dome-shaped, 2- to 5-mm skin-colored to slightly erythematous papules on the faces of three male and three female adults ranging from 18 to 48 years of age. All but one lesion were on the nose. Clinical differential diagnoses included fibrous papule, verruca, basal cell carcinoma, and a variety of other neoplasms. Histologically, dermal aggregates of clear cells with finely granular to vacuolated cytoplasm, and centrally located nuclei, were found. Most specimens also contained ectatic capillaries, and all showed evidence of irritation or trauma. Periodic acid-Schiff stain was negative in all specimens to which it was applied (5/6). Neural, melanocytic, and epithelial origins were eliminated by negative staining with S-100, Mart-1, cytokeratins, epithelial membrane antigen, and carcinoembryonic antigen, performed on some of the specimens. A mesenchymal nature was confirmed in one specimen staining strongly positive for vimentin. Five of six cases stained positively for CD68, and all five cases studied were strongly and diffusely positive for NKI/C3. Factor XIIIa stain highlighted scattered dendritic cells within the lesion but was otherwise negative in all six cases studied. Recognition of this variant of fibrous papule is important to distinguish this benign lesion from other clear cell neoplasms.