Invasive onychocytic carcinoma.

Neoplasms originating from nail matrix keratinocytes are very rare. Onychomatricoma and onychocytic matricoma are benign tumors arising from nail matrix keratinocytes. Only one case of onychocytic carcinoma, the malignant counterpart of onychocytic matricoma, has been reported in the literature. Herein, we describe a case of invasive onychocytic carcinoma. Two biopsy specimens of the tumor, obtained at early and invasive stages, were examined histopathologically. The first biopsy specimen showed a retiform proliferation of eosinophilic and basophilic cells in the nail matrix. The second biopsy specimen showed a retiform basophilic cell proliferation with focal keratinization. Similar to normal nail matrix keratinocytes, the proliferating basophilic cells failed to express cytokeratin (CK)1, CK6 and CK10. Focal expression of hair-specific keratins, including K31, K85 and K86, was observed. On the basis of these findings, the tumor was identified as an invasive malignant tumor originating from nail matrix keratinocytes.