Updated from 1:55 p.m. with XBiotech statement.

Results from a phase III study of Xilonix, a colon cancer drug developed by XBiotech (XBIT) - Get Report , have been deemed unreliable by the European Society of Medical Oncology (ESMO), according to a statement issued Thursday. 

Serious questions about the XBiotech colon cancer drug were raised after the Xilonix presentation at an ESMO cancer meeting on July 2. 

These questions prompted ESMO to review the XBiotech data again, led by Dr. Dirk Arnold of the Instituto CUF de Oncologia in Lisbon.

In a statement released by ESMO Thursday, Arnold said. "In conclusion, the jury is still out on whether the study made sense but as the results do not bear close inspection, they also cannot be relied upon. It's not yet clear whether there is any benefit in translating this trial into practice."

The full statement on XBiotech and its colon cancer drug Xilonix can be read here

"XBiotech is confident in the Xilonix Phase III data presented at ESMO. We fundamentally disagree with Dr. Arnold's interpretation of the data and look forward to further discussion in an appropriate scientific forum," said XBiotech spokesperson Mariann Caprino.

Arnold reviewed the Xilonix data at the ESMO meeting on July 2. Below is a photo taken of his summary slide:

XBiotech expects European regulators to approve Xilonix for colon cancer patients in the fourth quarter, based on the phase III study results submitted earlier this year. But the public disavowal of the Xylonix data by ESMO, a respected European cancer research group, lowers the probability of approval significantly. 

XBiotech shares fell 15% to $15.39 Thursday following the issuance of the ESMO statement. 

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