Expression of c-kit protein and mutational status of the c-kit gene in osteosarcoma and their clinicopathological significance. We examined c-kit protein expression and mutations of the c-kit gene in 40 human osteosarcoma samples to their relationship with clinicopathology and prognosis of the disease. The expression of c-kit protein was evaluated by immunohistochemistry and single-strand conformational polymorphism was performed to evaluate c-kit gene mutations in exons 11 and 17. Expression of c-kit protein occurred in 25 (62.5%) osteosarcoma samples. Patients with osteosarcomas with higher c-kit protein expression levels were significantly more likely to experience local disease recurrence and had a significantly lower survival time than patients with lower c-kit expression. We found no evidence of mutations in exons 11 or 17. This study suggests that c-kit protein expression might serve as a prognostic marker for osteosarcoma, however exons 11 and 17 might not be suitable targets for osteosarcoma treatments based on suppression of c-kit tyrosine kinase activity.