CYP19A1 and hepatocellular carcinoma: In this study, we first evaluated possible effects of interactions of carcinoma cells upon aromatase mRNA expression in HepG2 using a coculture systems of “separation.” The HCC cell line, HepG2, has been widely used as a substitute for “liver cell” in many previous in vitro studies and because it is relatively easy to evaluate compared to primary human hepatocytes.