The effect of exemestane on mRNA levels of aromatase in H23 and A549 cells. H23 and A549 cells were treated with 50 μM and 20 μM exemestane respectively and 48 h later, aromatase mRNA levels were studied with real time RT-PCR. Results are expressed as relative expression and normalized to untreated cells. Asterisks denote a statistically significant difference (unpaired t-test) compared to untreated cells. * P < 0.05.