NEW YORK ( TheStreet) -- Keryx Pharmaceuticals ( KERX) announced Monday the failure of its experimental colon cancer drug perifosine. Keryx shares fell 56% TO $2.16 in Monday pre-market trading. Shares of Aeterna Zentaris ( AEZS), which own ex-U.S. rights to perifosine, were down 63% to 79 cents. The failed phase III study enrolled 468 patients with advanced colon cancer, randomizing them to treatment with perifosine plus Roche's Xeloda or a placebo plus Xeloda. Perifosine failed to improve overall survival, the primary endpoint of the study, Keryx said. "We are all extremely disappointed with the results of the study," said Keryx CEO Ron Bentsur, adding that the company will evaluate whether or not to continue a separate phase III study of perifosine in multiple myeloma. Not everyone is surprised at perifosine's failure. University of Chicago oncologist Dr. Mark Ratain and I predicted the negative outcome of the colon cancer study last October. --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.