Department of Pathology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand Tel/Fax : +66 2 411 4260 ; E-mail : email@example.com Received : 24 September 2014 ; Accepted : 30 October 2014.
CD43 is commonly concerned as a marker for hematopoietic cells and, at times, a preferential T-cell marker. However, a number of non-hematologic cancers, mostly carcinoma, can express CD43. Recently, a case of malignant melanoma mimicking malignant lymphoma by cytomorphology was reported to express CD43 as well as melanoma markers but the other hematologic markers [Buehler et al. Diagn Cytopathol 2012;40:619- 23]. This is another case report. A 52-year-old man suffered from a rapidly growing left tonsillar mass for one month causing slurred speech. An incisional biopsy showed gray tissue and, beneath the epithelium, a sheet of large tumor cells with distinct nucleolus and somewhat distinct cell borders. Focal infiltration of the epithelium by tumor cells was noted. The first pathologist’s impression was hematologic malignancy, possibly plasmab- lastic lymphoma, as the original workup showed focal and faint CD138 expression but negative keratins and CD45. On consultation, hematologic malignancy and malignant melanoma were considered. The tumor cells express CD43, CD68 (focal), S-100, HMB45, Melan A, and vimentin. The negative markers included CD3, CD20, CD30, CD79a, MUM1, PAX5, kappa, lambda, and CK5/6. The proliferation index was high (70-75%) by Ki-67. Masson Fontana stain showed fine melanin pigment granules in only few tumor cells. In summary, another case report of malignant melanoma with CD43 expression, mimicking malignant lymphoma, raises the awareness of diagnostic pitfall when dealing with undifferentiated tumors showing only CD43 expression among various hematologic markers. A panel for keratins, vimentin, S-100, CD45, CD30, and CD138 will be helpful when dealing with undifferentiated large cell tumor.