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The use of adjuvant chemotherapy is indicated after resection of grade III or Kiupel high‐grade MCTs because of their high metastatic rate and for metastatic and unresectable MCTs. The use of chemotherapy after incomplete resection of grade I and II MCTs and Kiupel low‐grade MCTs is not indicated based on their lower metastatic potential.

Some of the chemotherapeutic agents that have reported activity against canine MCTs are prednisolone, vinblastine, CCNU (Lomustine), vinorelbine, and chlorambucil.

The response rate of macroscopic cutaneous MCTs to oral prednisolone as a single agent is reported to be 20% (McCaw et al. 1994). Most of these responses were partial responses with remission times between 10 and 20 weeks.

The reported response rates for single‐agent vinblastine range from 12 to 27% (Rassnick et al. 2008). Vinblastine is commonly administered to dogs at a dosage of 2.0 mg/m². The dose can be escalated to 3.0–4.0 mg/m² with neutropenia as the dose‐limiting toxicity (Vickery et al. 2008; Bailey et al. 2008).

CCNU (Lomustine) is an antitumor alkylating agent in the nitrosourea family. Lomustine is administered orally at a dose of 50–90 mg/m² every 21 days. A response rate of 47% for measurable cutaneous MCTs treated with single‐agent CCNU (90 mg/m²) is reported (Rassnick et al. 1999). Acute toxicities include neutropenia and thrombocytopenia. CCNU can cause a delayed, cumulative dose‐related, chronic hepatotoxicity that is irreversible and can be fatal (Kristal et al. 2004).