Utility of Sry-Related HMG-Box Gene 10 (SOX10) as a marker of melanoma in effusion cytology

Background The cytodiagnosis of melanoma in effusions can be challenging. Although immunohistochemical (IHC) stains such as HMB45, Melan A, and S-100 are often utilized; the role of Sry-related HMG-box gene 10 (SOX10) in the diagnosis of melanoma in effusions has not been previously reported. Methods A total of 14 confirmed melanoma cases diagnosed on effusion cytology (nine pleural and five peritoneal) were collected from 2000 to 2016. IHC stain for SOX10 was performed and compared with HMB45, Melan A, and S-100. To evaluate the specificity of SOX10, we stained 47 previously diagnosed nonmelanocytic malignant effusions. A cut-off of >1 positively staining cells was considered positive. The intensity of staining was graded as weak, moderate, and strong. Results All 14 melanoma cases were positive for SOX10 and HMB45 (100%), compared to 12 cases (86%) using Melan A and S-100. Among 47 previously diagnosed nonmelanocytic malignant effusions (4 malignant mesotheliomas, 12 mullerian tumors, 9 breast carcinomas, 9 lung adenocarcinomas, and 13 hematologic tumors), SOX10 and HMB45 showed a specificity of 98%, whereas Melan A and S100 had a specificity of 100%. Conclusions The sensitivity of SOX10 for melanoma in effusions is comparable with HMB45 with a 100% sensitivity. In terms of staining intensity, HMB45 appeared to be superior as it showed 100% moderate to strong intensity compared to 72% for SOX10. All four markers showed near-100% specificity in differentiating melanoma from nonmelanocytic malignant effusions. A combination of HMB45 and SOX10 might be useful as the initial stains of choice in diagnosing melanoma in effusion cytology.