HPGDS and cancer: The paradigm of allele frequency among the populations holds the key to unlock the existing problem of inter-individual genetic variation in xenobiotic metabolizing enzymes (XMEs) and in particular the decay or null allele frequency of Glutathione-S-transferase’s classes such as Mu 1 (GST M1) and Theta 1 (GST T1), which are considered as the major risk factor for various diseases including several types of cancers [8–10].