TERT and skin basal cell carcinoma: Thus, although we cannot exclude that of the ten CC>TT alterations detected (six c.-138_139CC>TT, three c.-124_125CC>TT and one c.-126_127CC>TT) some, or potentially even all, represent a preexisting C>T variation with an additional C>T mutation, we do believe these alterations, found in 13% of BCC and 18% of SCC, most likely primarily represent UV-exposure tandem mutations, arguing for UV-exposure inducing TERT promoter mutations in these tumors.