A prospective study of radiation therapy for the treatment of grade 2 mast cell tumors in 32 dogs.

Surgery, chemotherapy, and irradiation have been used singly or in combination to treat dogs with cutaneous grade-2 mast cell tumors (MCT). However, optimal treatment has not been established. At The Animal Medical Center, 32 dogs with grade 2, stage 0 MCT received cobalt radiation treatment to a dose of 54 Gy; 94% had a disease-free interval of 1 year. The 2-,3-,4-, and 5-year disease-free intervals were 86%. Survival rates were 100% for 1 year and 96% for 2 to 5 years, with only 1 death caused by MCT. Primary site was not a prognostic factor for survival in this study. Minimal toxicity was observed and was limited to acute cutaneous reactions. Late-term reactions to radiation therapy were mild and considered acceptable in all cases. No deaths occurred due to treatment, and no dog was eliminated from the study because of radiation therapy toxicity. Radiation therapy appears to be an effective treatment for dogs with grade 2, stage 0 MCT.

Radiation treatment for incompletely resected soft-tissue sarcomas in dogs.

OBJECTIVE: To evaluate efficacy of radiation for treatment of incompletely resected soft-tissue sarcomas in dogs. DESIGN: Prospective serial study. ANIMALS: 48 dogs with soft-tissue sarcomas. PROCEDURE: Tumors were resected to < 3 cm3 prior to radiation. Tumors were treated on alternate days (three 3-Gy fractions/wk) until 21 fractions had been administered. Cobalt 60 radiation was used for all treatments. RESULTS: Five-year survival rate was 76%, and survival rate was not different among tumor types or locations. Four (8%) dogs developed metastases. Eight (17%) dogs had tumor recurrence after radiation. Development of metastases and local recurrence were significantly associated with reduced survival rate. Median survival time in dogs that developed metastases was 250 days. Median disease-free interval for all dogs was 1,082 days. Median time to recurrence was 700 days. Dogs that developed recurrence after a prolonged period responded well to a second surgery. Acute radiation toxicosis was minimal; osteosarcoma developed at the radiation site in 1 dog. CONCLUSIONS AND CLINICAL RELEVANCE: An excellent long-term survival rate may be achieved by treating soft-tissue sarcomas in dogs with resection followed by radiation. Amputation is not necessary for long-term control of soft-tissue sarcomas in limbs. Development of metastases and recurrence of local tumors after radiation treatment are associated with decreased survival rate. Acute and delayed radiation toxicosis was minimal with the protocol used in this study.

Use of carboplatin for treatment of dogs with malignant melanoma: 27 cases (1989-2000).

OBJECTIVE: To evaluate response rate and duration of malignant melanomas in dogs treated with carboplatin. DESIGN: Retrospective study. ANIMALS: 27 client-owned dogs with spontaneously occurring measurable malignant melanomas. PROCEDURE: Records of dogs with melanomas treated with carboplatin from October 1989 to June 2000 were reviewed. Carboplatin was administered IV at doses of 300 or 350 mg/m2 of body surface area. Response to treatment and evidence of drug toxicity were determined. RESULT: Response to treatment could be evaluated in 25 dogs. Of those, overall response rate was 28%. One dog had a complete response, 6 (24%) dogs had a partial response (> 50% reduction in tumor burden). Median duration of partial response was 165 days. Eighteen dogs had stable disease (n = 9; 36%) or progressive disease (9; 36%). Response to treatment was significantly associated with carboplatin dose on a milligram per kilogram basis (15.1 mg/kg 16.9 mg/lb] of body weight vs 12.6 mg/kg [5.7 mg/lb]). Evidence of gastrointestinal toxicosis could be assessed in 27 dogs. Mean body weight of 5 dogs that developed gastrointestinal toxicosis was significantly less than that of 22 dogs without gastrointestinal toxicosis (9.9 kg [21.8 lb] vs 19.3 kg [42.5 lb]). CONCLUSIONS AND CLINICAL RELEVANCE: Carboplatin had activity against macroscopic spontaneously occurring malignant melanomas in dogs and should be considered as an adjunctive treatment for microscopic local or metastatic tumors. Gastrointestinal toxicosis was associated with body weight. Because small dogs are more likely to have adverse gastrointestinal effects, gastrointestinal protectants should be considered for these patients.

Tumors of the skin and associated structures.

Because of the location of skin tumors, afflicted dogs and cats are frequently presented to veterinarians for examination. The location also facilitates the use of radiation therapy for patients with skin tumors. Few animals treated with radiation therapy for skin tumors experience significant toxicity. Animals with a variety of skin tumors can benefit from treatment with radiation therapy. These tumors include mast cell tumors, squamous cell carcinoma, tumors of the digit, tumors of the ear canal, tumors of the cutaneous adnexa, mammary gland tumors, plasma cell tumors, cutaneous melanoma, cutaneous hemangiosarcoma, and transmissible venereal tumors. The prognosis for individual patients varies with the tumor type and, in some cases, with the stage of the disease.

The role of radiotherapy in the treatment of lymphoma and thymoma.

Chemotherapy is the mainstay of therapy for the treatment of lymphoma in dogs and cats. Radiation therapy can be utilized in the management of patients with solitary lymphoma and to induce a rapid local response in selected patients with multicentric lymphoma. A combination of surgery and radiation therapy can offer an excellent prognosis for cats with thymoma. Radiation therapy can also play a role in the management of dogs with thymoma.