Immunohistochemical Identification of HER-2/ neu Overexpression and CD117 (c-kit) Expression in Multiple Myeloma

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Abstract
Multiple myeloma (MM) is the most common plasma cell dyscrasia. Conventional therapy results in a median survival of 3-5 years. Patients with B-cell disorders and coexistent HER-2/neu overexpression in solid tumors have a poorer prognosis than those without an underlying B-cell disorder. This, and the recent success of the tyrosine kinase inhibitor, imatinib mesylate in chronic myelogenous leukemia, led us to evaluate the incidence and role of c-kit (CD117) and HER-2/neu overexpression in MM. We conducted a retrospective study to determine the incidence of HER-2/neu and c-kit overexpression in MM. HER-2/neu overexpression was evaluated using the DAKO Hercep test and c-kit overexpression was assessed using conventional immunohistochemistry (IHC); 69 patients with a diagnosis of MM were identified, of whom, 31 patients (19 males and 12 females) had an adequate pathological specimen available for IHC testing; 4 out of 31 patients (12.9%) showed HER-2/neu overexpression, while 5/31 (16.13%) showed CD117 expression. Two patients (6.45%) showed both HER-2/neu and c-kit overexpression. Although both HER-2/neu and c-kit are not expressed very frequently in patients with MM, there appears to be a subgroup of patients in whom, either one or both these oncogenes is overexpressed. Given our small sample size, it is difficult to comment on the effect of CD117 and/or HER-2/neu overexpression on survival. Future larger studies are needed to define the association in MM and to determine if the presence of one (CD117 or HER-2/neu) has an effect on overexpression of the other oncoprotein. Furthermore, it would be beneficial to identify the molecular nature of the interplay between HER-2/neu and c-kit, if any. Target-directed signal transduction inhibition therapy using tyrosine kinase inhibitors, may be a distinct possibility in a select group of patients with MM.