Expression of Sox10 and c-kit in sinonasal mucosal melanomas arising in the Chinese population.

Sinonasal mucosal melanomas (SNMM) of the head and neck regions are rare and aggressive malignancies. Although they can affect patients of any ethnicity, they are more numerous in Chinese patients. The diagnosis and treatment of these tumors can be challenging. Recent studies have reported that Sox10 is a sensitive melanocytic marker for cutaneous melanoma (Nonaka et al. in Am J Surg Pathol 32:1291-1298, 2008). In addition, a CD117 (c-kit) gene mutation has been identified in cutaneous melanomas, indicating that there may be potential therapeutic benefits of tyrosine kinase inhibitors, such as Imatinib. The purpose of this study was to detect and test the immunohistochemical expression of Sox10 and c-kit in mucosal melanomas (MM) arising in the nasal cavities of Chinese patients. Twenty eight patients with mucosal melanomas of the nasal cavity were treated in two major hospitals in China. All cases had been locally diagnosed as primary SNMM. We confirmed all diagnoses with positive immunohistochemical stains for S100 and HMB-45. Additionally, automated immunohistochemistry was performed using a goat polyclonal Sox10 antibody and a monoclonal c-kit antibody counterstained using a standard avidin-biotin complex method. Immunohistochemical positive expression of Sox10 was defined by nuclear stain; and positivity for c-kit resulted in a distinct membranous staining. The extent of nuclear positivity for Sox10 and membranous stain for c-kit was graded by 4 board certified pathologists as follows: 1+, 1-25 % of positive tumor cells; 2+, 25-50 %; 3+, 50-75 %; and 4+, ≥75 %. Sox10 nuclear expression was found in all cases (100 %), with 4+ staining in 26 out of 28 cases (92.8 %) and 3+ staining in two cases with (7.1 %). The overall positivity for S100 staining was 23 out of 28 (82.1 %), with 1+ staining in 10 cases, 2+ staining in 6 cases, 3+ staining in 7 cases, and no staining in 5 cases. The sensitivity and intensity of Sox10 immunohistochemistry were both higher than with S100 immunohistochemistry. Immunopositivity of membranous stain for c-kit (CD117) was seen in 24 out of 28 cases (85.7 %), including 6 tumors that were 4+, eight that were 3+, six that were 2+, and four that showed 1+ staining. Our results demonstrate that Sox10 is a sensitive marker for SNMM and it may possess diagnostic value in addition to that of S100 protein. The expression of c-kit in the majority of MMs suggests that it may be useful in the assessment of these tumors for potential treatment with tyrosine kinase inhibitors.