Long-Term Observation of the Progression From Nodal Marginal Zone Lymphoma to Diffuse Large B-Cell Lymphoma in a Dog

A 4-year and 10-month old female Pembroke Welsh Corgi presented with an enlarged right popliteal lymph node, and a histopathological diagnosis of nodal marginal zone lymphoma (nMZL) was made. After resection of the lymph node, follow-up observation was continued without chemotherapy. At 22 months after initial presentation, the dog developed enlargement of peripheral lymph nodes, and the histopathological diagnosis was late-stage nMZL. Multidrug chemotherapy induced clinical complete remission, but the tumor relapsed with enlargement of peripheral and abdominal lymph nodes 42 months after initial presentation. Second-round multidrug chemotherapy induced complete clinical remission again; however, the tumor relapsed with lymphadenopathy 47 months after initial presentation. The dog died 59 months after initial presentation, and postmortem examination revealed generalized lymphadenopathy; the histopathological diagnosis was diffuse large B-cell lymphoma (DLBCL). Polymerase chain reaction for antigen receptor gene rearrangements revealed that the nMZL and DLBCL samples were derived from the same B-lymphocyte clone.