PGP and neoplasm: 2003; Malmo et al., 2013). Given that tumors were excised from the animals at least 48 h after the last administration of the formulations (or later if tumors had not reached 1500 mm3), levels of P-gp might have returned close to normal. It is also valid to mention that, despite the advantage of being able to directly check the protein expression levels, immunoblotting uses total tumor lysate, which also contains nontumor stromal and infiltrating cells, preventing the distinction of P-gp in tumor and normal cells (Mechetner, 2007).