S100 A6 immunohistochemical staining for spindle cell and desmoplastic melanomas

To the Editor, S100A6, otherwise known as calcyclin, is a calcium-binding protein belonging to the S100 protein family. It has been found in fibroblastic and epithelial cell lines, cells with rapid proliferative activity and cells undergoing differentiation. S100A6 expression is present in a variety of cutaneous and non-cutaneous neoplasms. It has been well documented that melanomas, as well as other benign melanocytic lesions including some melanocytic nevi and blue nevi express S100A6. Approximately 62–100% of previously reported metastatic and primary melanomas have expressed S100A6. To our knowledge, there have been no reports evaluating desmoplastic or spindle cell melanomas using S100A6 expression. We reviewed 11 desmoplastic melanomas (Fig. 1) and three spindle cell melanomas, all of which were positive for polyclonal antibody S100 protein. These cases were retrieved from the archives at Geisinger Medical Center from 2002 to 2007 and stained with anti-S100A6 protein. We also reviewed five conventional melanomas, one noduloulcerative melanoma and two metastatic melanomas to the lymph nodes. These cases were also positive for polyclonal anti-S100 protein. Our results showed that all three spindle cell melanomas and 7 of 11 desmoplastic melanomas (63.6%) stained diffusely with anti-S100A6 protein (Figs. 2 and 3). One of the desmoplastic melanomas stained focally, while the three remaining desmoplastic melanomas (27.3%) did not stain with anti-S100A6. The conventional melanomas, noduloulcerative melanoma and metastatic melanomas all stained with anti-S100A6 in different distributions. Four of the five conventional melanomas stained diffusely, while the remaining melanoma had rare positive cells. The noduloulcerative melanoma stained diffusely with anti-S100A6. One of the metastatic melanomas stained positive in a patchy distribution and the other metastatic melanoma had rare positive cells.