Author: Assoc Prof Patrick Emanuel, Dermatopathologist, Auckland, New Zealand, 2017.
Clear cell mesenchymal neoplasm (CCMN) is a rare dermaltumour of uncertain lineage. The tumours have a benign clinical course but histologically closely resemble malignant tumours including dermalmetastases.
Histology of clear cell mesenchymal neoplasm
Histologically, these tumour arise in the dermis and are usually well circumscribed (figure 1). The cells of the tumour are clear, large cells (approximately 6–8 times the size of a stromal lymphocyte and about half the size of a subcutaneous adipocyte) that were oval to polygonal in shape with abundant clear cytoplasm (figure 2). Closer inspection revealed that, while many of the cells were optically clear, others contained lacy, reticular cytoplasm that had a slightly granular appearance (figure 3).
Special stains for clear cell mesenchymal neoplasm
These tumours are negative for immunohistochemical markers for various keratins, melanoma markers, and markers often seen in renal cell carcinoma (Pax-8, RCC).
Differential diagnosis of clear cell mesenchymal neoplasm
Metastatic clear cell carcinoma including renal cell carcinoma: This is probably the most important differential diagnosis. Numerous immunohistochemical studies including PAX-8, AE1/3, RCC,EMA need to be confirmed to be negative to exclude this possibility
Melanoma - CCMN is negative with the immunohistochemical markers for melanoma
PEComa - This tumour usually expresses melanocytic markers
Lazar AJ, Fletcher CD. Distinctive dermal clearcellmesenchymal neoplasm: clinicopathologic analysis of five cases. Am J Dermatopathol. 2004 Aug;26(4):273-9.