Doxorubicin-Induced Cardiotoxicity at Non-Cumulative Dose in a Dog with Multicentric Lymphoma

Doxorubicin is an effective chemotherapeutic agent widely used in veterinary oncology, particularly as part of the CHOP protocol for canine lymphoma.Despite its therapeutic benefit, cardiotoxicity remains a serious dose-limiting adverse effect.Although clinically significant cardiotoxicity is typically reported at cumulative doses of 150-240 mg/m 2 in dogs, functional cardiac deterioration has been observed at lower doses, with progression to congestive heart failure rarely reported.This case report describes doxorubicin-induced cardiotoxicity below the established cumulative threshold in a dog with multicentric lymphoma, which presented with overt clinical signs of congestive heart failure, including coughing, syncope, and pleural effusion.The dog also exhibited marked echocardiographic changes, including right atrial enlargement and a reduction in fractional shortening from 33% to 21% over 2 weeks, ultimately resulting in death 53 days after symptom onset.The clinical diagnosis was supported by the temporal relationship with doxorubicin administration and serial cardiac imaging findings.This case highlights that severe cardiotoxicity can occur even below traditionally accepted cumulative thresholds, reinforcing the importance of individualized, ongoing cardiac monitoring and early intervention, regardless of dose.