Qualitative interviews with ten dog owners established the five adverse effects cited most frequently as reasons not to pursue chemotherapy for canine cancer therapy: reduced appetite, vomiting, diarrhoea, alopecia, exercise intolerance. A questionnaire was designed to identify the level of belief amongst dog owners that canine chemotherapy caused these toxicities using a five part Likert scale. The questionnaire was served upon dog owners attending a primary care practice for vaccination or attending a medical referral practice for treatment of dogs with non-neoplastic or neoplastic disorders. The effect of the following factors on this level of belief was assessed using multivariable ordinal logistic regression: owner age, gender, socioeconomic status, and experience of chemotherapy for themselves, for a relative or friend, or for a previously or currently owned pet.

One hundred and eighteen owners completed questionnaires: 28% primary care vaccination, 16% referral non-neoplasia, 56% referral neoplasia. Respondent age ranged from 22 to 81 years (median 51). 70% were female. 2.5% had experienced chemotherapy as part of their personal healthcare, 60% as treatment for a friend or relative, and 47% as treatment for a pet. 2% respondents presenting a dog without neoplasia had owned a pet that had received chemotherapy. 17% respondents presenting a dog with neoplasia had never owned a pet that had received chemotherapy.

Respondents who had owned a pet receiving chemotherapy were significantly less likely to agree that dogs receiving chemotherapy have a poor appetite (OR 0.37 [0.19, 0.72]), vomiting (0.13 [0.06, 0.28]), diarrhoea (0.25 [0.13, 0.50]), alopecia (0.12 [0.06, 0.25]), or exercise intolerance (0.50 [0.26, 0.98]). Older respondents were significantly more likely to agree that dogs receiving chemotherapy have vomiting, diarrhoea, and exercise intolerance. For diarrhoea this effect was linear (1.03 [1.01, 1.06]) whilst for vomiting (age>40years 4.22 [1.88, 9.51]) and exercise intolerance (age>30years 8.53 [1.83, 39.7]) it was categorical. No other variables were significantly associated with outcomes.

Owners consider adverse effects as reasons not to pursue chemotherapy for cancer in their dogs. Owners without experience of chemotherapy for a pet are significantly more likely to believe that chemotherapy will cause adverse effects in dogs than owners with experience of companion animal chemotherapy. Interaction between these two client groups may increase uptake of chemotherapy for dogs with cancer.