MENLO PARK, Calif. ( TheStreet) -- Geron's ( GERN) lead cancer drug imetelstat was dealt a serious setback Monday after a mid-stage breast cancer study was stopped early for futility. A second study in lung cancer is continuing even though results are only expected to be "modest," the company said. Without imetelstat, Geron's drug pipeline wears dangerously thin. The company's controversial embryonic stem cell programs were abandoned last year, leaving Geron with just an experimental drug for brain metastases in early phase II studies. Geron shares are down $1.44, or 50%, to $1.46 in Monday pre-market trading. More patients with advanced breast cancer treated with imetelstat and the chemotherapy drug paclitaxel were dying or progressing faster than patients treated with paclitaxel alone, according to an interim analysis of the phase II study. As a result, the study was discontinued. An unplanned interim analysis of the ongoing imetelstat phase II study in non-small cell lung cancer revealed that the drug was showing a "modest" trend toward delaying tumor progression compared to paclitaxel, Geron said. However, the benefit of adding imetelstat to paclitaxel was not clinically meaningful so Geron will not move ahead with a phase III study. Two additional phase II studies of imetelstat in blood-related cancers are continuing. Imetelstat is designed to inhibit telomerase, an enzyme that promotes cell division. Telomerase is normally blocked and inactive in healthy cells but is switched on in cancer cells. Geron finished the second quarter with approximately $118 million, or 90 cents per share, in cash and securities on hand. --Written by Adam Feuerstein in Boston. >To contact the writer of this article, click here: Adam Feuerstein. >To follow the writer on Twitter, go to http://twitter.com/adamfeuerstein. >To submit a news tip, send an email to: firstname.lastname@example.org. Follow TheStreet on Twitter and become a fan on Facebook.