The role of R21 expression in differential diagnosis of melanocytic lesions

Cyclic adenosine monophosphate (cAMP) is an intracellular signal transmitter involved in the regulation of melanocyte growth, proliferation, and melanogenesis. R21 is a monoclonal antibody against the soluble adenylyl cyclase (sAC) protein. Various nuclear and cytoplasmic R21 expression patterns in melanocytic lesions have been previously reported. Pan-nuclear staining was defined as specific for melanoma and was found supportive in the assessment of surgical margins.

The aim of this study is to evaluate the different expression patterns of R21 immunostain and investigate its effectiveness in the differential diagnosis of cutaneous malignant and benign melanocytic lesions.

Fifty invasive cutaneous melanoma and 50 benign melanocytic proliferation were included in the study.

Paraffin blocks that best reflected tumor morphology were studied via immunohistochemical staining for R21. For all patterns, the cases showing staining in 25% or more tumor cells were considered as positive.

Yates' Chi-square, Pearson Chi-square exact test, Spearman correlation were used.

Dot-like Golgi staining was characteristic for nevi (12/50) and seen only in one melanoma. Pan-nuclear staining was striking for melanoma (36/50). This pattern was observed in 2 dysplastic and 3 common melanocytic nevi too. None of the Spitz nevi expressed R21 in pan-nuclear pattern. For the diagnosis of melanoma, sensitivity and specificity of the pan-nuclear expression were 72% and 90%, respectively. Positive and negative predictive values were found as 87% and 76%. R21, a second-generation immunohistochemical marker, can be used in the differential diagnosis of benign and malignant melanocytic lesions.