XBiotech Inc. plunged a record 50 percent after a late-stage study of its lead drug, using an unconventional method to evaluate its cancer-fighting abilities, raised questions about any potential benefit for patients.

Rather than the traditional approach of tracking tumor growth, the study reported on symptoms associated with disease progression, such as pain, fatigue, appetite and muscle loss, according to a company statement distributed Saturday. The study authors didn’t compare survival in patients given the drug -- Xilonix for colorectal cancer -- or placebo, a standard method of assessing effectiveness, because everyone in the trial was offered the drug after eight weeks, XBiotech said.

The shares fell 40 percent to $14.91 at 11:40 a.m. in New York, after earlier dropping to $12.50. XBiotech had risen 41 percent in the past 12 months through Friday, largely in response to positive reports about Xilonix’s progress.

The study, presented at the European Society of Medical Oncology meeting in Barcelona, was from the third and final stage of research typically needed to win regulatory approval of a new drug. Patients who showed a “clinical response” to treatment, either the drug or a placebo, had a higher survival rate, according to the study. Patients given the drug were more likely to respond to treatment, with 33 percent showing “anti-cancer activity,” compared with a 19 percent response rate among those given placebo, according to the statement.

The trial involving 302 patients was designed in collaboration with the input of a scientific advisory working group from the European Medicines Agency, according to Austin, Texas-based XBiotech. A decision on whether to approve the medicine for use in Europe could come by the end of the year.

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