Prognosis of primary pulmonary adenocarcinoma after surgical resection in small‐breed dogs: 52 cases (2005‐2021)

BACKGROUND: Tumor size is an important prognostic factor in lung cancer in dogs, and the canine lung carcinoma stage classification (CLCSC) recently has been proposed to subdivide tumor sizes. It is unclear if the same classification scheme can be used for small‐breed dogs. OBJECTIVES: To investigate whether the tumor size classification of CLCS is prognostic for survival and progression outcomes in small‐breed dogs with surgically resected pulmonary adenocarcinomas (PACs). ANIMALS: Fifty‐two client‐owned small‐breed dogs with PAC. METHODS: Single‐center retrospective cohort study conducted between 2005 and 2021. Medical records of dogs weighing <15 kg with surgically resected lung masses histologically diagnosed as PAC were examined. RESULTS: The numbers of dogs with tumor size ≤3 cm, >3 cm to ≤5 cm, >5 cm to ≤7 cm, or >7 cm were 15, 18, 14, and 5, respectively. The median progression‐free interval (PFI) and overall survival time (OST) were 754 and 716 days, respectively. In univariable analysis, clinical signs, lymph node metastasis, margin, and histologic grade were associated with PFI, and age, clinical signs, margin, and lymph node metastasis were associated with OST. Tumor size classification of CLCS was associated with PFI in all categories, and tumor size >7 cm was associated with OST. In multivariable analysis, tumor size >5 cm to ≤7 cm and margin were associated with PFI, and age was associated with OST. CONCLUSIONS AND CLINICAL IMPORTANCE: The tumor size classification of CLCS would be an important prognostic factor in small‐breed dogs with surgically resected PACs.