Technique, pharmacokinetics, toxicity, and efficacy of intratumoral etanidazole and radiotherapy for treatment of spontaneous feline oral squamous cell carcinoma.

The histologic appearance, locoregional recurrence, and rate/site of metastases of spontaneous feline oral squamous cell carcinoma are similar to head and neck cancer in humans. A feasibility study of intratumoral Etanidazole, a hypoxic cell sensitizer, and radiation therapy were instituted in this model. Eleven cats with feline squamous cell carcinoma were treated with intratumoral Etanidazole and radiation therapy. Total Etanidazole doses were 1.5-24.0 gms/m2 (0.5-6.9 gms). The tumor partial response rate was 100% (11/11); the median volume regression was 70%. All cats have died as a result of tumor recurrence or tumor-related complications. Median survival was 116 days. Ten cats have been autopsied. Non-necrotic and necrotic tumor cells were identified at the treatment site in all cats. Pharmacokinetic studies were performed in six cats. Following intravenous infusion, the plasma elimination of the Etanidazole was biexponential. The systemic availability following intratumoral administration was 61.2 +/- 21.1%. Peak plasma Etanidazole levels were observed 14 minutes following intratumoral injection, after which elimination was biexponential. Thirty minutes following intratumoral Etanidazole administration, tumor Etanidazole levels were 62.8% of plasma levels. Feline squamous cell carcinoma appears to be a useful model of human head and neck cancer. Cats tolerate substantial doses of intratumoral and intravenous Etanidazole. Etanidazole and radiation therapy cause rapid regression, but not cure, of feline squamous cell carcinoma. There is a similarity between the intravenous kinetics of Etanidazole in humans and cats. Further studies in this model are planned.