ERCC2 and cancer: When dividing tumors into four categories (Ta/T1 low, Ta/T1 high, T ≥ 2 low, and T ≥ 2 high), evident differences were found only in muscle-invasive carcinomas, with the homozygous wild type genotype of the XPD gene (codon 312) being associated with low grade cancer, whereas the frequencies of genotypes containing a variant Asn allele were significantly increased in high grade neoplasms (Figure 3(a)).