GSTM1 and thyroid cancer: Other thyroid cancer studies showed that only the combination of GSTM1 and GSTT1 null inheritance [53] or only the presence of three potentially risk alleles, namely GSTM1-null, GSTT1-null and GSTP1 A1578G genotype GG [46], leads to significant increase in adjusted odds ratio for papillary and follicular thyroid cancers.