An immunohistochemical comparison between MiTF and MART-1 with Azure blue counterstaining in the setting of solar lentigo and melanoma in situ.

Background: Evaluation of cutaneous pigmented lesions can be diagnostically challenging and represents an activity often supplemented by immunohistochemistry. Immunohistochemical studies typically employ 3,3'-diaminobenzidine (DAB) resulting in brown staining of both melanocytes and melanin. Difficulty may thus arise in distinguishing different cell types in heavily melanized lesions. Azure blue counterstaining has been used in conjunction with melanoma antigen recognized by T-cells (MART-1) to differentiate melanocytes from melanin by highlighting the latter blue-green. Microphthalmia transcription factor (MiTF) represents an alternative immunomarker that shows nuclear reactivity, which facilitates ease of interpretation.

Methods: Twenty examples of solar lentigo and melanoma in situ (MIS) were independently evaluated utilizing MiTF and MART-1/Azure blue for melanocyte quantification. Melanocyte counts were averaged over five high-power fields (×400) to obtain a mean melanocytic count.

Results: There was no significant difference in the mean melanocytic count between MART-1/Azure blue and MiTF as assessed in the solar lentigo group and as assessed independently in the MIS group. MiTF nuclear staining facilitated interpretation and required less laboratory preparation, as an additional counterstain was not necessary.

Conclusions: MiTF is as effective as MART-1/Azure blue in identifying melanocytes in the context of solar lentigo or MIS. On the basis of our results, we favor expanding the use of MiTF as an immunohistochemical marker, as it provides an efficient alternative to MART-1 with Azure blue counterstaining in the evaluation of cutaneous pigmented lesions.