ERCC2 and xeroderma pigmentosum: Importantly, the XP cluster 2 score genes ERCC1 and ERCC2 were individually highly significantly negatively correlated with TIS score (p = 0.0002, R = −0.186 and p = 0.0004, R = −0.176), immune infiltration genes and the XP cluster 1 score (Figure 3).