Reliability of immunostaining using pan-melanoma cocktail, SOX10, and microphthalmia transcription factor in confirming a diagnosis of melanoma on fine-needle aspiration smears

BACKGROUND Accurate fine-needle aspiration (FNA) diagnosis of metastatic melanoma is of therapeutic and prognostic significance and often requires ancillary studies. To the authors' knowledge, the reliability of immunostaining using a pan-melanoma cocktail, Sry-related HMG-BOX gene 10 (SOX10), and microphthalmia transcription factor (MITF) in confirming a diagnosis of melanoma on FNA smears has not been studied to date. METHODS This retrospective study included 50 FNA cases with a definitive diagnosis of melanoma. Twenty-nine cases were epithelioid type (group 1), and 21 cases were predominantly spindle cell type with or without an epithelioid component (group 2). Each case was immunostained using pan-melanoma cocktail, SOX10, and MITF. Staining intensity and the percentage of positive cells were recorded. RESULTS The pan-melanoma cocktail was positive in 43 cases (86%), SOX10 was positive in 50 cases (100%), and MITF in 45 cases (90%). SOX10 and MITF demonstrated nuclear staining with stronger and more diffuse staining with less or no background staining compared with pan-melanoma cocktail, which displayed cytoplasmic staining. For pan-melanoma cocktail and SOX10, the detection rates were identical in groups 1 and 2 (86% with pan-melanoma cocktail and 100% with SOX10). For MITF, the detection rate was higher in group 1 compared with Group 2 (93% vs 86%). CONCLUSIONS In the current study, SOX10 was found to have the highest overall detection rate, followed by MITF and pan-melanoma cocktail. The pan-melanoma cocktail and SOX10 performed equally well for groups 1 and 2, and MITF had a higher detection rate in group 1. Overall, SOX10 and MITF appeared to be superior to the pan-melanoma cocktail and SOX10 seemed better than MITF in confirming a diagnosis of melanoma on FNA smears.