SOX10 immunostaining distinguishes desmoplastic melanoma from excision scar.

Sry-related HMG-BOX gene 10 (SOX10), a nuclear transcription factor that plays an important role in schwannian and melanocytic cell differentiation, has recently been shown to be a useful marker in the diagnosis of melanocytic and schwannian tumors. Fibroblasts and histiocytes that could histopathologically mimic melanoma cells often express S100, which complicates the evaluation of melanoma excision specimens for residual tumor. Distinguishing melanoma cells from immature fibrocytes or histiocytes is made more challenging in desmoplastic melanoma excision specimens. We compared the utility of melanoma markers [SOX10, S100, HMB-45, Melan-A and micropthalmia transcription factor (MiTF)] in 3 invasive, 9 desmoplastic and 14 intraepidermal melanomas. We also evaluated 18 excision scars. The staining intensity for all the cellular components in melanoma and scar specimens was scored. SOX10 strongly highlighted all in situ, invasive and desmoplastic melanomas. In contrast, MiTF expression was weak to absent in desmoplastic melanomas. In scars, S100 highlighted background spindled fibrocytes and histiocytes with greater intensity than SOX10. MiTF highlighted multi-nucleated histiocytes, while SOX10 did not. Our results showed that SOX10 was strongly expressed by desmoplastic melanoma. Furthermore, SOX10 was less likely than S100 and MiTF to be expressed by background fibrocytes and histiocytes within scars.