Comparison of c-Kit expression between primary and metastatic melanoma of skin and mucosa.

Background: Melanoma causes the greatest morbidity and mortality of all skin cancers. Mucosal melanoma is a rare but highly aggressive neoplasm. According to previous studies the prevalence of KIT mutations in acral lentiginous and mucosal melanomas is relatively low (less than 15-20%), but it can have profound therapeutic implications for localized high risk or metastatic diseases. Our goal was to evaluate c-Kit expression in different types of primary and metastatic melanoma to discriminate potential candidates for targeted therapy.

Methods: We designed a cross-sectional study and selected 50 cases of malignant melanoma (primary, metastatic cutaneous, and mucosal) from the affiliated hospitals of Shiraz University of Medical Sciences in the period of 2008 to 2012. Immunohistochemistry for KIT expression was performed. Multistage sampling method was selected for sampling and chi-square test was used for statistical analysis.

Results: In our study, male to female ratio was 1.77. The male sex was correlated with higher tumor stage (p< 0.05). 62% (n= 31) of cases showed at least 5% of KIT-positive cells, consist of 18% (n= 9) with 5-50%, 16% (n= 8) with 51-95%, and 28% (n= 14) of cases showed more than 95% of cells expressing KIT. But in 38% (n= 19) of cases KIT expression was less than 5% of positive cells. Tumor stage was positively correlated with tumor cell immunoreactivity and intensity (p< 0.05). Metastatic melanoma showed lower percentage (43%) of positivity. Intensity of staining and percentage of positive cells were positively correlated (p< 0.001).

Conclusion: In primary melanomas, significant KIT expression was found by immunohistochemistry, which may be useful to screen the patients for advising to KIT mutation analysis and targeted therapy.