Lymphoma is a common canine tumor. Diffuse large B cell lymphoma is the most common type of B cell lymphoma in dogs, but there are less common B cell lymphoma types that have aggressive behavior and little is known about the mechanisms driving these tumors. The goal of this study is to genetically characterize these less common forms and compare these findings to diffuse large B cell lymphoma. This will inform whether targeted therapies for diffuse large B cell lymphoma, including ones developed for human patients, are useful for other B cell lymphoma types. Investigators will also study patient outcome in these cases to identify prognostic factors and work to develop tests that more accurately diagnose clinically important subtypes of B cell lymphoma. This work will improve our understanding of canine B cell lymphoma to advance diagnosis and prognosis and develop better therapies to improve outcomes.