PGP and lymphoma: Based on these previous results, the aim of this retrospective single-center trial was to: (1) evaluate which factors could predict the response to treatment in dogs with IRE; (2) evaluate whether the lack of response could be related to the duodenal epithelial and lamina propria lymphocyte expression of P-gp; (3) evaluate whether a previous treatment with steroids could induce higher expression of duodenal P-gp; and (4) differentiate inflammatory disease vs. lymphoma in duodenal samples of NRE dogs by immunophenotypic evaluation of the lymphocyte infiltrate and clonality testing.