Advanced Metastatic Melanoma With C-KIT (CD117) Immunohistochemical Expression: A Case Report and Therapeutic Considerations

Melanoma is an aggressive malignancy characterized by significant molecular heterogeneity and poor prognosis in advanced stages. Activating KIT mutations occur predominantly in acral and mucosal melanoma subtypes and may represent actionable therapeutic targets. However, immunohistochemical expression of C-KIT (CD117) should not be interpreted as evidence of an activating KIT mutation, as molecular confirmation is required before targeted therapy can be considered. We report the case of a 39-year-old man with rapidly progressive metastatic melanoma involving the lungs, liver, and central nervous system. Histopathological examination demonstrated metastatic melanoma with positive C-KIT (CD117) immunohistochemical expression. Because of the patient's rapid clinical deterioration before referral for comprehensive molecular evaluation, molecular characterization could not be completed, precluding confirmation of activating KIT mutations and assessment for targeted therapy. This case highlights the importance of distinguishing immunohistochemical protein expression from actionable molecular alterations, emphasizes the value of timely molecular testing in advanced melanoma, and illustrates the practical challenges of implementing precision oncology in patients presenting with advanced-stage disease.