Renal Cell Carcinoma Bone Metastasis: Epidermal Growth Factor Receptor Targeting

Renal cell carcinoma frequently metastasizes to the skeleton in the later stages of the disease. Patients with bone metastasis from renal cell carcinoma experience severe pain, neurologic compromise, and frequent pathologic fractures. These tumors are relatively resistant to chemotherapy and radiation, and the 5-year survival of patients is less than 10%. The epidermal growth factor receptor is overexpressed in human renal cell carcinoma and hypothesized to be a potential target in the treatment of bone metastasis. Using in vitro studies, it was shown that blockade of the epidermal growth factor receptor was effective in decreasing proliferation and receptor autophosphorylation of a human bone-derived renal cell carcinoma cell line. In an experimental nude mouse model, treatment with Taxol and protein tyrosine kinase inhibitor 166, a small molecule receptor tyrosine kinase inhibitor, blocked the growth of renal cell carcinoma in the tibia and resulted in decreased bone destruction. The use of protein tyrosine kinase inhibitor 166 and Taxol was cytostatic and nontoxic in long-term animal experiments. Epidermal growth factor receptor blockade is an exciting potential therapy for renal cell carcinoma bone metastasis in humans, but because it is cytostatic rather than cytotoxic, its optimal role may be as a supplement to cytotoxic chemotherapy. It ultimate role and its relationship to other therapeutic interventions remains to be elucidated and validated.