Correlation between initial and long-term responses of spontaneous pet animal tumors to heat and radiation or radiation alone.
Most early-phase testing of new therapeutic modalities involves analysis of initial tumor response as opposed to estimation of long-term response. In this study, the validity of initial response rates to predict long-term responses was examined for tumors treated with radiotherapy alone compared with heat combined with radiotherapy. A total of 130 pet animals with either squamous cell carcinomas, melanomas, fibrosarcomas, mammary adenocarcinomas, or mast cell sarcomas were randomized to receive either radiation alone (XRT) or heat + radiation (delta + XRT). Responses to treatment were evaluated by response rates and response duration. The complete response (CR) rates were consistently higher for delta + XRT than for XRT across different histology groups. The combined therapy led to prolonged tumor response in all histological subgroups except melanomas, which had a longer response duration when treated with XRT alone (p = 0.043). This was in spite of a relatively high CR rate in that group (100% versus 12.5% for delta + XRT and XRT, respectively). In contrast, while no significant improvement in CR rate was observed for dermal squamous cell carcinomas treated with delta + XRT (XRT = 52.9%; delta + XRT = 68.8%), a significant improvement in response duration was noted (p = 0.002). These are two examples where CR rate did not predict long-term response. When all histological subgroups were combined (except melanomas), the CR rate was higher (p less than 0.001), and response duration was prolonged (p = 0.031) for delta + XRT compared to XRT alone.
D000818:Animals; D000829:Animals, Domestic; D002371:Cat Diseases / Q000532:radiotherapy / Q000628:therapy*; D002415:Cats; D003131:Combined Modality Therapy; D004283:Dog Diseases / Q000532:radiotherapy / Q000628:therapy*; D004285:Dogs; D005500:Follow-Up Studies; D006358:Hot Temperature / Q000627:therapeutic use*; D008545:Melanoma / Q000628:therapy / Q000662:veterinary; D009369:Neoplasms / Q000532:radiotherapy / Q000628:therapy / Q000662:veterinary*