Microphthalmia transcription factor immunohistochemistry for FNA biopsy of ocular malignant melanoma

Microphthalmia transcription factor (MiTF) is a sensitive and specific immunohistochemistry (IHC) marker for malignant melanoma (MM) in surgical resections, but its utility in cytology specimens has not been extensively studied.

A search of the pathology database identified fine-needle aspiration biopsies signed out as MM or suspicious for MM (1998-2012). The final diagnosis and the IHC results were recorded, and all slides were re-reviewed. MiTF IHC (C5/D5 cocktail) was performed on alcohol-fixed, Papanicolaou-stained direct smears. Any amount of nuclear staining was considered positive. Staining was scored on a scale of 1 to 4 (1, 1%-24%; 2, 25%-49%; 3, 50%-74%; 4, 75%-100%).

Two hundred seventy-four cases were diagnosed as MM, and 24 were diagnosed as suspicious for MM. IHC staining was performed for 25% (69 of 274) of the MM cases and for 33% (8 of 24) of the cases suspicious for MM. MiTF IHC of Papanicolaou slides was performed for 37% (101 of 274) of the MM cases (positive, 82% [83 of 101]; negative, 4% [4 of 101]; noncontributory, 14% [14 of 101]) and for 33% (8 of 24) of the cases suspicious for MM (positive, 38% [3 of 8]; noncontributory, 62% [5 of 8]). The majority of positive staining was scored as 3 or 4. The sensitivity of MiTF on Papanicolaou-stained slides was 95%.

MiTF is a useful IHC stain for the evaluation of ocular MM, and it is effective when it is performed on alcohol-fixed, Papanicolaou-stained aspirate smears.