Meanwhile, NO can also reduce platelet aggregation by decreasing Ca2+ level in platelets, thus inhibiting the integrity of tumor blood vessels and ultimately enhancing the EPR effect [48]; (4) P-glycoprotein (P-gp), one of the adenosine triphosphate (ATP) binding cassette transporters, is over-expressed in tumor cell membranes [30,49]. Here, ABCB1 is linked to neoplasm.