Updated with current side effect data on regorafenib.EMERYVILLE, Calif. ( TheStreet) --Treatment with Bayer's experimental drug regorafenib prolonged the lives of patients with advanced colon cancer by about six weeks compared to best supportive care, according to results from a phase III study released Tuesday night ahead of an upcoming medical conference. The smallish survival benefit favoring regorafenib was good enough for Bayer to stop the study early and declare victory but the extra six weeks of life comes at a significant cost. Regorafenib caused severe and painful sores on the hands and feet of 17% of patients in the study; another 10% of patients suffered from serious fatigue while 7% experienced severe diarrhea. Later this year, Bayer intends to seek regulatory approval of regorafenib for the treatment of colon cancer in patients who have exhausted all other medical options. Bayer has not disclosed what it plans to charge for regorafenib if approved, but under a settlement reached last fall, Onyx Pharmaceuticals ( ONXX) will receive a 20% royalty on worldwide sales of the drug. Researchers will present the regorafenib trial on Jan. 21 at the Gastrointestinal Cancers Symposium sponsored by the American Society of Clinical Oncology but the media embargo on the data was lifted Tuesday night. Regorafenib is a once-daily pill that works by blocking several molecular pathways that cancer cells use to grow and feed off the body's blood supply. Regorafenib was designed to be an improved version of Nexavar, the kidney and liver cancer drug originally developed by Onyx that was partnered with Bayer. Like Nexavar, regorafenib doesn't shrink tumors much at all. Instead, the drug appears to benefit patients by putting tumors into stasis, which then helps patients live a bit longer. The phase III study enrolled 760 colon cancer patients who were no longer responding to currently approved treatments. The patients were randomized to receive regorafenib plus best supportive care or best supportive care plus a placebo. After a second interim analysis, patients treated with regorafenib demonstrated a median overall survival of 6.4 months compared to 5 months for patients treated with best supportive care. The relative risk of death was reduced by 23% following regorafenib treatment. Regorafenib did not shrink tumors significantly more than best supportive care, nor did the drug delay the time before tumors started growing again. "It's a modest benefit but a benefit nonetheless," said Onyx spokesperson Lori Melancon. "We believe the results are clinically meaningful because these are patients in the last line of therapy who have no other treatment options." Approximately 15,000 colon cancer patients in the U.S. and Europe no longer respond to treatment with several drugs including Roche's ( RHHBY) Avastin, Eli Lilly's ( LLY) Erbitux and Amgen's ( AMGN) Vectibix and will therefore be eligible for further therapy with regorafenib, according to a Jefferies estimate which pegs the colon cancer opportunity at around $300-400 million.
Other analysts view regorafenib's colon cancer opportunity as smaller, perhaps $200 million to $300 million. Bayer, in a recent investor presentation, said regorafenib could generate $1 billion in revenue based on possible approvals in multiple cancer types including colon cancer and GIST, or stomach, cancer. Next up for investors focused on colon cancer drugs will be results from a phase III study of Keryx Pharmaceuticals' ( KERX) perifosine due later this quarter. Regorafenib represents potential competition although the colon cancer patients enrolled in the perifosine study were not as advanced or heavily pre-treated those who participated in the regorafenib trial. Onyx shares closed Tuesday down fractionally to $43.86. --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.