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Chemotherapy protocols for mast cell tumour

Chemotherapy is used in the neoadjuvant setting (to shrink tumours and make excision possible) or as anti-metastatic treatment in tumours that have metastasized or high-risk tumours (high grade and/or elevated miotic index). Conventional chemotherapy is not recommended for the prevention of recurrence of incompletely resected MCTs, as further surgery or radiation are considered more effective; if a medical option is required in this context, a tyrosine kinase inhibitor (toceranib or masitinib) should be used first prior to conventional chemotherapy.

A number of chemotherapy protocols have been reported. The most commonly used protocol includes vinblastine and prednisolone as shown below.

Vinblastine 2 mg/m i.v. once. Prednisolone 2 mg/kg p.o. q24h

Vinblastine 2 mg/m i.v. once. Prednisolone 1.5 mg/kg p.o. q24h

Vinblastine 2 mg/m i.v. once. Prednisolone 1 mg/kg p.o. q24h

Vinblastine 2 mg/m i.v. once. Prednisolone 1 mg/kg p.o. q24h

Vinblastine 2 mg/m i.v. once. Prednisolone 1 mg/kg p.o. q24h

Vinblastine 2 mg/m i.v. once. Prednisolone 1 mg/kg p.o. q24h

Vinblastine 2 mg/m i.v. once. Prednisolone 1 mg/kg p.o. q24h

Vinblastine 2 mg/m i.v. once. Prednisolone 1 mg/kg p.o. q24h

• Catheters should be placed in all cases and only catheters placed by ‘first-stick’ should be used for chemotherapy.

• GI protectants are recommended. Omeprazole (1 mg/kg q24h or q12h) is often used by oncologists. Ranitidine with sucralfate is an alternative approach. Cimetidine is avoided due to its effect on the hepatic cytochrome P450 enzyme pathway and the potential for altering metabolism of chemotherapeutics.

• Certain breeds (generally Collie type) may be more sensitive to vinblastine due to the mutation; a commercial test is available. Suggested monitoring:

• Haematology is checked prior to each treatment. • Biochemistry is checked prior to the first treatment.

Myelosuppression or GI effects may occur. Vinblastine is a vesicant, therefore catheters should be placed in all cases and only catheters placed by ‘first-stick’ should be used. Should an extravasation occur, contact an oncologist. Treatment can be given if the neutrophil count is > 3 × 10/l and platelet count > 100 x10/l. If the neutrophil count is < 3 × 10/l, then suspend treatment and recheck in 5 – 7 days. If neutrophil count is < 1 × 10/l, prescribe prophylactic antibiotics (until neutrophil count is >1 × 10/l). If neutrophil count is < 1 × 10/l and the patient is pyrexic or unwell, administer i.v. antibiotics and contact an oncologist for advice. If the neutrophil count is < 1 x 10/l, decrease dose of the causative chemotherapy drug by 10%; if recurrent, contact an oncologist for advice.

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Ideally, restaging should be performed at week 12 for high-risk tumours without known metastasis and after week 4 and at week 12 for tumours with known metastasis. If restaging is clear, further restaging is recommended every 3 months (for a year) for high-risk tumours. 

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If additional metastatic lesions are identified (liver, spleen or lymph nodes), or treatment fails to yield remission further, treatment with lomustine or a tyrosine kinase inhibitor is indicated (contact an oncologist).

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