Prognostic significance of hypermethylation of death‐associated protein kinase (DAPK) gene CpG island in dogs with high‐grade B‐cell lymphoma

Death‐associated protein kinase (DAPK) is a serine/threonine kinase and a tumour suppressor gene. Diffuse large B‐cell lymphomas with inactivated DAPK through hypermethylation of a CpG island is known to result in a biologically aggressive phenotype in humans. This retrospective study was carried out to analyse the prognostic significance of DAPK CpG island hypermethylation in canine lymphoma. We hypothesized that DAPK CpG island hypermethylation can be a negative prognostic indicator in dogs with nodal high‐grade B‐cell lymphoma. Forty‐seven dogs with high‐grade B‐cell lymphoma, according to the updated Kiel classification, were evaluated after being treated with a CHOP (vincristine, cyclophosphamide, doxorubicin and prednisolone)‐based chemotherapy protocol. The methylation status of the DAPK CpG island was examined by methylation‐specific PCR. Progression‐free survival (PFS) and overall survival (OS) were compared using the Kaplan‐Meier analysis and log‐rank test. The cox proportional hazard regression model was used to evaluate the effect of multiple variables. Hypermethylation of the DAPK CpG island was detected in 21 of the 47 dogs. The PFS and OS in dogs with the hypermethylation (median: 220 and 266 days, respectively) were significantly shorter than those of dogs without hypermethylation (median: 301 and 412 days, respectively) (PFS, P = .036; OS, P = .007). In the multivariate analysis, hypermethylation of the DAPK CpG island remained an independent prognostic factor in predicting shortened PFS (P = .047) and OS (P = .021) as well as clinical substage b. Overall, hypermethylation of the DAPK CpG island was a negative prognostic factor in canine high‐grade B‐cell lymphoma.