YKL-40 expression in naevocellular naevi, carcinomas and melanomas of the skin

18019 Background: Elevated serum levels of the protein YKL-40 are associated with a poor prognosis in several solid tumors including melanoma (H. Schmidt, JCO 2006, Cancer 2006 in press). YKL-40 is secreted by cancer cells, macrophages and neutrophils. The function of YKL-40 is only poorly understood. It may be a growth or differentiation factor, play a role in angiogenesis or protect against apoptosis. The aim was to describe the tissue expression of YKL-40 in naevocellular naevi, carcinomas and melanomas of the skin by immunohistochemistry. Methods: Paraffin-embedded tissue sections from 40 patients with different naevocellular naevi, carcinomas and melanomas of the skin were developed with EnVision+ System-HRP K4007 (DakoCytomation) using a monoclonal antibody against YKL-40. The intensity of YKL-40 staining was scored using a semi-quantitative method. Results: YKL-40 protein expression appeared as a cytoplasmic, granular staining with no staining of membranes, nuclei or extracellular matrix. In normal skin the basal epithelial layer stained weakly positive. Melanocytes and melanophages stained negative. Macrophages and leucocytes stained positive. Hair follicles, sebaceous glands and sweat glands stained positive. Three basal cell carcinomas all stained positive. In 10 squamous cell carcinomas, the epidermal components stained positive and the invasive tumor islands were negative. In 3 keratoacanthomas, the epithelial components as well as the infiltrative tumor islands stained positive. In naevi (2 junctional, 5 compound and 1 intradermal) the epithelial components stained positive, the intradermal components stained negative. In melanomas the tumor cells stained positive in 9 of 10 specimens. Both the epidermal and the invasive components of melanomas stained positive. Three melanoma metastases all stained positive. Conclusions: YKL-40 is expressed in normal skin and in benign and malignant lesions of the skin. Generally, YKL-40 expression is increased in cells of high activity, although the invasive tumor islands of squamous cell carcinomas stain negative. In melanomas, the tumor cells may be a source of the elevated YKL-40 serum levels observed in these patients. No significant financial relationships to disclose.