Chemotherapy is appropriate adjunct to surgery for oral melanoma in dogs

By Sarah Guy, MedWire Reporter

The addition of chemotherapeutic treatment with carboplatin for dogs with oral malignant melanomas that have undergone surgical excision may be a reasonable alternative to adjunctive radiotherapy, report researchers.

After the surgery‑carboplatin combination, the team observed similar overall progression-free survival (PFS) rates and overall survival (OS) rates as previous studies have recorded for surgery‑radiotherapy protocols.

Overall however, the median survival rate of their 17-dog cohort was just over 1 year, suggesting that "dogs diagnosed with oral malignant melanoma have a poor long-term prognosis, despite treatment with adjuvant chemotherapy for presumed microscopic disease," say Gillian Dank (Hebrew University, Rehovot, Israel) and colleagues.

The majority of oral melanomas in dogs exhibit malignant behavior, characterized by invasion of surrounding tissues, and local, regional, as well as distant metastasis, they explain in Veterinary Comparative Oncology.

The team evaluated survival outcomes of a median 300 mg/m² body surface area, four-dose, carboplatin regimen initiated in dogs treated surgically either with (n=11) or without (n=6) radiotherapy.

Initial tumors were most commonly located in dogs' tongues (29%), followed by rostral mandible and lip (18% each). The most common clinical sign at presentation was an oral mass (53%), report the researchers.

After a median follow-up time of 329 days, 11 dogs (65%) had relapsed, and the median PFS was 259 days for the entire group. PFS in dogs treated with surgery and chemotherapy was 210 days, versus 291 days in dogs given surgery, radiation, and chemotherapy.

Of note, the proportion of dogs with local recurrence was lower in those that received radiotherapy compared with those that did not (27 vs 67%), suggesting that surgery has limitations in terms of eradicating local disease, say Dank and co-workers.

The dogs survived a median 440 days, with the initial oral tumor causing death in over half (59%) of cases. Neither disease stage (measured using World Health Organization criteria for canine melanoma), treatment with radiation therapy, nor carboplatin dose were significantly associated with shorter PFS or OS, remark Dank et al.

"Surgery and carboplatin chemotherapy may be a reasonable alternative treatment option when radiation is cost prohibitive or is not available," conclude the authors, who recommend that future prospective studies should be based on uniform dosing for the entire study group.

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