SOUTH SAN FRANCISCO ( TheStreet) -- Treatment with Exelixis' ( EXEL) experimental drug cabozantinib helps patients with a form of thyroid cancer significantly extend the time before their disease worsens, according to results from a late-stage study announced Monday. Based on the results from this phase III trial, Exelixis said it will seek permission from the U.S. Food and Drug Administration to submit cabozantinib for approval. Exelixis expects the approval filing to be fully submitted in the first half of next year. Exelixis shares closed Friday at $5.99. The phase III study enrolled 315 patients with advanced medullary thyroid cancer and randomized them to treatment with cabozantinib or a placebo. Patients treated with cabozantinib had a 72% reduction in the risk of disease progression compared to placebo patients. At the median, cabozantinib delayed tumor progression by 11.2 months compared to 4 months for placebo -- a 7.2-month difference which was statistically significant and met the primary endpoint of the study. Exelixis did not disclose any other results, including safety data, from the study pending presentation at an upcoming medical meeting. The study was designed to later measure the potential of a survival benefit for cabozantinib but given the overwhelmingly positive results announced Monday, Exelixis said it may consult with FDA to change the study design to allow patients in the placebo arm to receive cabozantinib. Exelixis is also developing cabozantinib in prostate cancer and hopes to begin phase III studies before the end of the year. --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.