SLC22A2 and hepatocellular carcinoma: To confirm the finding of a significantly lower expression of SLC22A1 in HCC, mRNA levels of SLC22A1, SLC22A2, and SLC22A3 were determined by real-time PCR analysis in a cohort of 22 fresh-frozen HCC tissues and adjacent non-tumor liver samples (HCC study population set 2; Tables S1 and S3 in Additional file 1).