Are severe adverse events commonly observed in dogs during cancer chemotherapy? A retrospective study on 155 dogs

Overall prevalence of severe adverse events (sAE) has been poorly studied in veterinary medicine and peer-reviewed studies mostly focused on a single protocol, making it difficult to have a general overview. The aim of this retrospective study was to assess the frequency and risk factors of sAE secondary to various protocols of chemotherapy in dogs. Medical records of 155 dogs receiving chemotherapy between January 2013 and December 2018 were reviewed. Adverse events (AE) were graded according to Veterinary Comparative Oncology Group-common terminology criteria for AE (VCOG-CTCAE) grading system. Statistical analyses were performed to determine whether demographic, cancer type and chemotherapy protocol were associated with development of sAE and their consequences. AE were reported at least once in 124 (80%) dogs and sAE were observed in 50 (32.3%) dogs. Among them, 23 (14.8%) had gastro-intestinal and 31 (20.0%) had myelotoxic events. sAE led to hospitalisation in 37 (23.9%) dogs, to chemotherapy arrest in 12 (7.7%) dogs and to euthanasia or death in 9 (5.8%) dogs. Haematopoietic tumours were statistically associated with a higher frequency of sAE (p = .004), gastrointestinal sAE (p = .009) and hospitalisation (p = .004). A body weight over 10 kg was associated with less haematological sAE (p < .001). The use of a multi-agent protocol was highlighted as a risk factor for sAE (p = .038) and haematological sAE (p < .001). sAE following chemotherapy and leading to hospitalisation, chemo arrest or death were relatively common. A special attention during chemotherapy follow-up should be given to small dogs and those receiving multi-agent protocol or treated for haematopoietic tumours.