A Keratoacanthoma With Squamous Cell Carcinoma Under Immunosuppressive Therapy After Renal Transplantation

A 69-year-old Japanese male developed a solitary keratoacanthoma with squamous cell carcinoma (SCC) on his right arm. He had undergone kidney transplantation from his father due to chronic renal failure approx. 45 years earlier and had since been under immunosuppressive treatment (azathioprine and prednisolone). An immunohistopathological examination revealed Ki67- and p53-positive cells in the tumor bed of the keratoacanthoma, and our final diagnosis was a solitary keratoacanthoma with SCC. In this case, several factors apparently caused the solitary keratoacanthoma with SCC: the long duration of immunosuppression, the use of azathioprine after renal transplantation, and UV exposure. Immunohistopathological studying is important for the diagnosis of SCC or keratoacanthoma. Keratoacanthomas have malignant potential, and this patient's SCC could have been caused by the keratoacanthoma.