Mast cell tumour in dogs: masitinib vs placebo — POSSIBLE

In dogs with unresectable mast cell tumours, does masitinib delay tumour progression vs placebo?

Shelf #108 · gate-verified and displayed under the developer's blinded-trial rule

POSSIBLE: Masitinib delayed tumour progression in one large double-blind, randomized, placebo-controlled phase III trial of 202 dogs with nonmetastatic recurrent or nonresectable grade II or III mast cell tumours: median time to tumour progression was 118 days on masitinib versus 75 days on placebo (P = .038) — an absolute gain of 43 days, with the overall P value close to the significance line. The effect looked stronger when masitinib was used as first-line therapy (median time to progression 253 vs 75 days, P = .001), a subgroup finding that supports but cannot upgrade the main result. Overall survival was among the outcomes assessed, but the abstract reports no survival figures, so no survival claim is carded. This shelf rests on that one trial, stated on its face. Drafted Nov 10, 2026 (VetMed build, topic #108); all figures from abstracts fetched and verified at drafting.

Hahn 2008: masitinib stretched median time to tumour progression from 75 to 118 days (P = .038) in 202 dogs

Double-blind, randomized, placebo-controlled phase III clinical trial (record's own Methods wording); indexed as Randomized Controlled Trial

Who: Dogs: 202 client-owned dogs with nonmetastatic recurrent or nonresectable grade II or III mast cell tumours, in a double-blind, randomized, placebo-controlled phase III clinical trial — masitinib 12.5 mg/kg/day orally or placebo; time to tumour progression, overall survival, objective response at 6 months and toxicity were assessed.

Result: Masitinib increased overall median time to tumour progression compared with placebo from 75 to 118 days (P = .038). The effect was more pronounced when masitinib was used as first-line therapy, with median time to progression increasing from 75 to 253 days (P = .001), and held regardless of whether tumours expressed mutant KIT (83 days versus not reached, P = .009) or wild-type KIT (66 versus 253, P = .008), in the record's own ordering. Masitinib was generally well tolerated, with mild (grade I) or moderate (grade II) diarrhoea or vomiting as the most common adverse events. The abstract reports no overall-survival or 6-month response figures.

Watch out: Single trial carries this shelf (stated on its face). The headline P value (.038) is close to .05 and the median gain is 43 days overall; the much larger first-line figure (253 vs 75 days) is a subgroup result and should not be quoted as the trial's main effect. No survival benefit is shown on this record.

Hahn KA, Ogilvie G, Rusk T et al. Masitinib is safe and effective for the treatment of canine mast cell tumors. J Vet Intern Med. 2008;22(6):1301-9. PMID: 18823406. Registry ID: none in the record. MeSH: Animals · Antineoplastic Agents · Benzamides · Disease Progression · Dog Diseases · Dogs · Double-Blind Method · Female · Male · Mastocytoma · Piperidines · Pyridines · Thiazoles

Synthesis: a real but modest delay in progression, strongest as first-line therapy

Synthesis

Who: Synthesis of the card above: Hahn 2008 (double-blind, randomized, placebo-controlled phase III trial, 202 dogs with nonmetastatic recurrent or nonresectable grade II/III mast cell tumours).

Result: One large, properly blinded placebo-controlled trial found masitinib delays progression by a median of about six weeks overall, and by much more in the first-line subgroup — enough to card the delay as POSSIBLE, not enough, on a single trial with a borderline overall P value, to card it higher. Alongside the toceranib shelf (#107), the honest picture is that KIT inhibition works against canine mast cell tumours; masitinib's carded claim is delayed progression, toceranib's is objective response, and neither record cards a survival gain.

Watch out: Do not cross-compare the two drugs from these separate trials: different populations (masitinib's dogs were nonmetastatic), different endpoints and different eras. Mild-to-moderate diarrhoea and vomiting were the commonest adverse events in the masitinib trial.

Synthesis of Hahn KA et al. PMID: 18823406. Registry ID as on the individual card.

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