c-KIT is a receptor tyrosine kinase, which activates the PI3K, JAK/STAT, and MAPK pathways to promote cell survival and proliferation. Simple variants in KIT are seen in about 12.3% of all tumors. KIT variants are common in, and diagnostic for, gastrointestinal stromal tumor in 85% of cases. They are also seen in about 8% of melanomas. Specific KIT mutations predict prognosis and response or resistance to KIT inhibitors.