PAX5 and lymphoma: Considering this, in the present study, we aimed to: (1) compare the immunolabeling results in RSC and the matched CB (obtained from surplus effusion fluids or needle rinse fluid) of canine and feline lymphomas using CD3 and PAX5 markers; (2) determine the interobserver agreement in defining the immunophenotype by RSC and by CB; (3) assess the influence of pre-analytical variables, such as species, time of archive and coverslipping on positivity, intensity, background, and non-specific staining in immunolabeling with a membranous and a nuclear lymphoid marker on RSC.