ESR1 and lung cancer: In addition to EGFR, ALK etc, the estrogen receptor is another promising targeting gene.[3] Many studies have demonstrated that estrogens (ERS) and estrogen signaling play a significant role not only in normal lung development but also in lung cancer pathophysiology.[4,5] Cell lines derived from lung tumors of both men and women express estrogen receptors (ER) and respond to estrogens.