The KIT receptor tyrosine kinase (CD117 antigen) is found in a variety of normal tissue cell types and in several malignant tumors, including acute myeloid leukemia. We recently encountered two tumors initially suspected as acute myeloid leukemia cutis and expressing CD117 that showed punctate positivity for cytokeratin 20 diagnostic for Merkel cell carcinoma. We evaluated 20 additional cases of MCC and found that 21 of 22 tumors (95%) expressed CD117. Intensity of CD117 expression did not appear to correlate with aggressive behavior. While the function of the KIT receptor in MCC is not known, its pathogenic role in other malignant neoplasms suggests the possibility of a similar role in MCC.
From the Department of Pathology (L.D.S., D.R.F., L.L., P.U., B.S., R.V.) and Dermatology (L.D.S., D.R.F., L.L.), University of Michigan Medical Center, Ann Arbor, Michigan, U.S.A.
This study was approved and exempted from continuing review by the University of Michigan Medical Institutional Review Board for Human Subject Research.
Address correspondence and reprint requests to Lyndon Su, M.D., Department of Pathology, Division of Dermatopathology, University of Michigan Medical Center, Medical Sciences I, M5224, Ann Arbor, MI 48109-5224 U.S.A. E-mail: firstname.lastname@example.org