RASSF1 and skin basal cell carcinoma: Thus, our findings do not support a contribution of UVB exposure to the observed promoter hypermethylation of SHH, APC, SFRP5 and RASSF1A. The intriguing observation that nBCC and iBCC harbored more frequent methylation for these four genes compared with sBCC might indicate that DNA methylation contributes to the development or evolution of BCC.