Introduction: Cancer is a leading cause of mortality in older dogs. Despite the prevalence of chemotherapy in canine oncology, a good understanding of owners’ observations of side-effects and clinical signs in real-time is still lacking. Owners’ perceptions and reporting of clinical signs play an important role in monitoring a dog's condition during treatment and the use of digital owner-reported outcome measures could prove efficient in tracking chemotherapy side effects in the home environment. This could improve care and draws inspiration from the human use of patient-reported outcome measures in oncology.

Objective: To develop and test a prototype digital measure to monitor clinical signs and health-related quality of life in dogs undergoing chemotherapy, aiming to improve owner participation in their monitoring and enhance veterinary care.

Methods: A rapid literature review was conducted to identify existing measures and their methodological limitations. Items were generated based on the Veterinary Comparative Oncology Group - Common Terminology Criteria for Adverse Events, existing client reported outcome measures, and expert veterinary opinion. Proof-of-Concept testing was performed with 29 dog owners with pets undergoing chemotherapy. Participants completed daily assessments of their dog’s clinical signs and weekly quality of life surveys over a 21-day period. A sub-sample participated in cognitive interviews to assess content validity and acceptability. Descriptive statistics were used to assess clinical signs and quality of life scores. Internal consistency and item discrimination were evaluated, and qualitative data were analysed thematically.

Results: High adherence was reported, with a median of 21 daily and 3 weekly assessments completed. Participants found the assessments acceptable and beneficial. Fatigue, polydipsia, and anorexia were the most frequently reported clinical signs. Dogs experienced a median of 3 different clinical signs. The quality-of-life scale showed good internal consistency (Cronbach’s α = 0.84). Participants appreciated the daily assessments, found them easy to complete, and believed the measure could help improve monitoring and decision-making during chemotherapy.

Conclusion: The prototype tool, the Canine Cancer Outcome Measure (CAN-COM), demonstrated feasibility and acceptability for use by owners in the home environment for dogs undergoing chemotherapy. With further refinement and validation, such a tool could improve the monitoring of adverse events and support decision-making in veterinary oncology, enhancing the welfare of canine cancer patients.