It was reported that, in the treatment of childhood acute lymphoblastic leukemia (ALL), 3435 TT (two copies of the “T” allele) or CT (one copy of “C” and “T” allele) genotypes were associated with lower P-glycoprotein levels than in the CC genotype, resulting in a better permeability of substrates for P-gp (e.g., doxorubicin, epirubicin, vincristine) [54]. This evidence concerns the gene PGP and acute lymphoblastic leukemia.