Mediastinal Lymphoma in 70 Dogs Treated With Lomustine or Anthracycline-Based Multi-Agent Chemotherapy.

Primary mediastinal lymphoma is rare in dogs and literature exploring this disease is limited. Therefore, the aim of this study was to describe presentation, treatment and outcome in a large cohort of dogs with mediastinal lymphoma and explore prognostic factors including chemotherapy protocol. This retrospective multi-institute study included 70 dogs with primary mediastinal lymphoma treated with lomustine-based (LOP/LOPP) or anthracycline-based (CHOP/CEOP) chemotherapy. Most immunophenotyped cases were of T-cell lineage (95.6%). The majority were substage b (90%) and hypercalcaemia was noted in 69.1% of dogs. Clinical and objective response rates to chemotherapy were 92.7% and 97.9%, respectively, with 76.6% of dogs achieving a complete response. Median progression free survival (PFS) was 132 days (95% CI 83-181), and median overall survival time (OST) was 223 days (95% CI 175-271). The 6-month, 1-year, and 2-year survival rates were 55.7%, 22.9%, and 15.7%, respectively. On multivariable analysis, factors associated with longer PFS included hypercalcaemia (p = 0.041), chemotherapy-induced neutropenia (p = 0.014) and CD4+/CD8- immunophenotype (p = 0.004). Neutropenia at diagnosis was associated with shorter PFS (p = 0.015) and OST (p = 0.004). Other factors associated with shorter OST included granular morphology (p = 0.023) and CD4+/CD8+ immunophenotype (p = 0.004). Chemotherapy-induced neutropenia was associated with improved OST (p = 0.042). Differences in outcome between anthracycline- or lomustine-based chemotherapy protocols were not statistically significant. Overall, the prognosis for primary mediastinal lymphoma in dogs is poor to fair when treated with multi-agent chemotherapy. This is the second study associating hypercalcaemia with improved PFS in dogs with non-indolent T-cell lymphoma. Results also suggest prognostic significance of specific CD4/CD8 expression patterns.