Analysis of prognostic factors and patterns of failure in dogs with malignant oral tumors treated with megavoltage irradiation

Alain P. Théon From the Department of Surgical and Radiological Sciences (Théon, Madewell) and the Veterinary Medical Teaching Hospital (Rodriguez), School of Veterinary Medicine, University of California, Davis, CA 95616-8745.

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 DVM, MS
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Carlos Rodriguez From the Department of Surgical and Radiological Sciences (Théon, Madewell) and the Veterinary Medical Teaching Hospital (Rodriguez), School of Veterinary Medicine, University of California, Davis, CA 95616-8745.

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Bruce R. Madewell From the Department of Surgical and Radiological Sciences (Théon, Madewell) and the Veterinary Medical Teaching Hospital (Rodriguez), School of Veterinary Medicine, University of California, Davis, CA 95616-8745.

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 VMD, MS

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Objective

To determine quality and duration of progression-free survival (PFS) time in dogs with malignant oral tumors after definitive megavoltage irradiation, to analyze prognostic factors for PFS time and patterns of failure, and to analyze the influence of tumor recurrence and development of metastasis on survival.

Design

Prospective clinical trial.

Animals

105 dogs with squamous cell carcinoma, fibrosarcoma, or malignant melanoma of the oral cavity without evidence of metastasis.

Procedure

Dogs were treated with 48 Gy over 4 weeks on an alternate-day schedule of 4 Gy/fraction. Multivariate analysis was done by use of Cox's regression model to determine significant prognostic factors and by use of a competing risk model to determine the differential effects of prognostic factors on type of, and time to, failure. In 8% of the dogs, severe acute radiation reactions in the final week of treatment resulted in treatment discontinuation. In 7.6% of the dogs, chronic radiation reactions, including bone necrosis and fistula formation, developed.

Results

Prognostic factors that independently affected PFS time were histologic type and tumor T stage. Histologic type significantly influenced pattern of failure, but not time to failure, whereas clinical stage significantly influenced time to failure, but not type of failure.

Clinical Implications

Irradiation was a safe and effective treatment of malignant oral tumors. Because the local efficacy of radiation was influenced only by tumor size, early treatment of oral tumors should improve the prognosis. In dogs without tumor recurrence, systemic metastases, rather than regional metastases, limited long-term survival after radiation therapy. (J Am Vet Med Assoc 1997;210:778–784

Objective

To determine quality and duration of progression-free survival (PFS) time in dogs with malignant oral tumors after definitive megavoltage irradiation, to analyze prognostic factors for PFS time and patterns of failure, and to analyze the influence of tumor recurrence and development of metastasis on survival.

Design

Prospective clinical trial.

Animals

105 dogs with squamous cell carcinoma, fibrosarcoma, or malignant melanoma of the oral cavity without evidence of metastasis.

Procedure

Dogs were treated with 48 Gy over 4 weeks on an alternate-day schedule of 4 Gy/fraction. Multivariate analysis was done by use of Cox's regression model to determine significant prognostic factors and by use of a competing risk model to determine the differential effects of prognostic factors on type of, and time to, failure. In 8% of the dogs, severe acute radiation reactions in the final week of treatment resulted in treatment discontinuation. In 7.6% of the dogs, chronic radiation reactions, including bone necrosis and fistula formation, developed.

Results

Prognostic factors that independently affected PFS time were histologic type and tumor T stage. Histologic type significantly influenced pattern of failure, but not time to failure, whereas clinical stage significantly influenced time to failure, but not type of failure.

Clinical Implications

Irradiation was a safe and effective treatment of malignant oral tumors. Because the local efficacy of radiation was influenced only by tumor size, early treatment of oral tumors should improve the prognosis. In dogs without tumor recurrence, systemic metastases, rather than regional metastases, limited long-term survival after radiation therapy. (J Am Vet Med Assoc 1997;210:778–784

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