FOXP3 and B-cell non-Hodgkin lymphoma: The aim of the present study was therefore to document the presence of FOXP3+ Tregs in the resident T cell population of affected lymph nodes of dogs with B cell lymphoma (BCL) and to test the hypothesis that intra-tumoral CD4+FOXP3+ Tregs have a negative impact on treatment outcome, making comparisons with dogs with T cell lymphoma (TCL), non-neoplastic causes of lymphadenomegaly, and metastatic mast cell tumors (MCTs).