Melan A (QR138) Melanoma Marker IHC

NordiQC Assessment Run 74 2025: Optimal staining result with clone QR138! Melan A, also known as MART-1, is a melanocytic differentiation marker. Although its precise biological function is not fully understood, the antigen is specific for the melanocyte lineage and is expressed in normal skin, retina, and melanocytes, but not in other normal tissues. Melan A is thus a highly useful marker for benign and malignant melanocytic tumors. It is expressed in the vast majority of malignant melanomas and is considered a valuable component of the standard immunohistochemical panel for melanoma diagnosis. Recent findings from NordiQC Assessment Run 74 suggest that the clone QR138 may mark a turning point in Melan A immunohistochemistry. Although a generally low performance was observed in Run 74, the clone QR138 achieved optimal staining results for Melan A. In contrast, the monoclonal antibody clone A103, despite being the most widely used antibody (employed by 90% of participating laboratories), exhibited reduced affinity for low-level Melan A expression in malignant melanomas. Consequently, only 26% of A103-based protocols achieved sufficient staining, and merely 1.5% produced optimal results. These differences contributed to the historically low overall pass rate of 34%, with only 9.5% of results classified as optimal.