Efficacy of radiation therapy for incompletely resected grade-III mast cell tumors in dogs: 31 cases (1987-1998).

Objective: To determine the efficacy (durations of remission and survival) of an alternating-day radiation protocol for incompletely excised histologic grade-III solitary mast cell tumors (MCTs) in dogs.
Design: Retrospective study.
Animals: 31 dogs.
Procedure: Radiation (52 Gy in an 18-fraction alternating-day protocol) was delivered to an area bordered by margins > or = 3 cm around the surgical scar and to the associated local-regional lymph nodes. Dogs were not given chemotherapeutic agents concurrently or after radiation. Information on signalment, duration of remission, and survival time was obtained from medical records.
Results: Median and mean durations of remission were 27.7 and 17.0 months, respectively (range, 1 to 47 months). Median and mean durations of survival were 28 and 20 months, respectively (range, 3 to 52 months). Dogs with tumors located on the skin of the pinna, perineum, and prepuce had a median duration of remission greater than dogs with tumors located at other sites (27.7 and 14.4 months, respectively). Dogs with tumors < or = 3 cm in maximum diameter before surgery survived longer than dogs with tumors > 3 cm (31 and 24 months, respectively). The remission rate was 65% and survival rate was 71% at 1 year after treatment. Sixteen dogs that were euthanatized had complications associated with local-regional tumor progression. Systemic metastases to liver, spleen, intestine, and bone marrow were detected in 1 dog.
Conclusions and Clinical Relevance: Without further treatment, incompletely excised grade-III mast cell tumors have high local-regional recurrence; local-regional treatment with radiation may effectively be used to manage many such tumors.