Development and progression of proteinuria in dogs treated with masitinib for neoplasia: 28 cases (2010‐2019)

Objectives To describe the incidence, severity and progression of proteinuria over the first 6 months of masitinib treatment in tumour‐bearing dogs without pre‐existing proteinuria. To describe the effect of treatment on urine protein:creatinine and renal parameters in patients with pre‐existing proteinuria. Materials and Methods Records were reviewed from patients receiving masitinib for neoplasms between June 1, 2010, and May 5, 2019. Patients without pre‐treatment and at least one urine protein:creatinine after ≥7 days treatment were excluded. Signalment, tumours and concurrent diseases, treatments, haematology, biochemistry and urinalysis results before, during and after treatment for up to 202 days were collected. Patient visits were grouped into six timepoints for analysis. Results Twenty‐eight dogs were included. Eighteen percent of dogs non‐proteinuric at baseline (four of 22) developed proteinuria during treatment, all within 1 month of treatment initiation. One dog developed hypoalbuminaemia, none developed oedema or ascites, azotaemia or were euthanased/died due to proteinuria. Masitinib was immediately discontinued in both dogs in which urine protein:creatinine greater than 2.0 was detected and in both, proteinuria improved. Six dogs with pre‐treatment proteinuria were treated with masitinib, significant worsening of proteinuria did not occur. Neither azotaemia nor severe hypoalbuminaemia occurred. Clinical Significance Proteinuria, when it occurs, tends to develop within 1 month of masitinib commencement and may progress rapidly. Weekly proteinuria monitoring should be considered for the first month and a urine protein:creatinine greater than 0.5 should prompt reassessment within 1 week. Masitinib treatment can be considered in patients with pre‐treatment proteinuria and does not inevitably cause worsening of proteinuria.