c-kit (CD117) reactivity in extramedullary myeloid tumor/granulocytic sarcoma

Context.-c-kit, a proto-oncogene, encodes the transmembrane tyrosine kinase receptor CD117 and is detected by flow cytometry in the majority of cases of acute myeloid leukemia. The prognostic significance of the presence of c -Kit in acute myeloid leukemia is debated. Recently, c-kit inhibitors have been studied as possible therapies against hematopoietic malignancies; ther efore, c-Kit detection may have important implications for treatment. Objectives.-In this study, we investigated the expression of c-Kit in granu locytic sarcoma (GS) using paraffin-embedded tissue. Design.-Routinely formalin-fixed, paraffin-embedded tissues from 30 cases o f GS were studied using immunohistochemistry. c-Kit (C-19) (a polyclonal an tibody against carboxy terminal domain of c-Kit p145 or CD117) reactivity w as compared with myeloperoxidase and lysozyme. The immunohistochemical pane l also included CD34, CD68, CD43, Bcl-2, CD45RB, CD20, CD3, CD10, terminal deoxynucleotidyl transferase (TdT), and CD79a. Results.-The morphologic patterns included well-differentiated (5 cases), p oorly differentiated (19 cases), and blastic forms (6 cases). Clinical data were obtained from 28 of 30 patients. Granulocytic sarcoma presented in ly mph nodes in 10 cases, whereas in 20 cases it presented in extranodal sites . c-Kit reactivity was found in 87% (26/30) of the GS cases. There was no sig nificant difference in c-Kit positivity between the nodal (90%, 9/10) and e xtranodal (85%, 17/20) neoplasms. c-Kit expression was not associated with the degree of the myeloid maturation. Two of 13 lymphoblastic lymphoma cont rol cases and 1 of 28 of the large B-cell lymphomas were weakly immunoreact ive with c-Kit. Conclusions.-c-Kit reactivity can be demonstrated in a high percentage of G S cases; its presence may be useful not only in diagnosis, but also in the treatment of GS with new modalities.