What happened

XBiotech (NASDAQ:XBIT) is up 12.5% at 2:54 p.m. EDT after being up as much as 27% Friday following a jump of more than 26% on Thursday. Investors appear to be pouring into the biotech ahead of data from a phase 3 trial testing its colorectal cancer drug Hutruo, which used to go by the name Xilonix, that will be presented at the American Society of Clinical Oncology (ASCO) meeting Saturday.

So what

XBiotech released some of the data ahead of time, pointing out that 40% of patients receiving a full regimen of Hutruo -- referred to as "per protocol" patients -- achieved the primary endpoint, which was a combination of patient-reported symptoms and radiographic results, compared to just 23% of patients who received placebo.

While that's an impressive improvement, it's based on per protocol patients while regulators usually require a benefit based on all the patients that enroll in the study regardless of whether they finish, which is referred to as "intent to treat." Looking at patients that received at least one dose, but didn't necessarily finish the study, the results drop to 33% responders for those receiving Hutruo and 19% for the placebo group.

Paper with "Diagnosis: colon cancer" written on it.

Image source: Getty Images.

More importantly, this is just rehashed data that regulators at the European Medicines Agency have already said aren't sufficient to gain marketing approval because they didn't like the composite primary endpoint.

Xbiotech noted that the median survival of patients that met the primary endpoint was 11.7 months versus 5.7 months for those who didn't achieve the primary endpoint, arguing that the composite endpoint is a meaningful clinical endpoint. Unfortunately, this type of post-hoc analysis is generally frowned upon by regulators who would like to see the primary survival endpoint established before the trial begins.

Now what

Rather than focusing on the data at ASCO, investors would be better off waiting for the data from a second phase 3 trial, which is measuring overall survival as a primary endpoint. The trial is scheduled to have its second interim peek at the data in June, and if positive, could be the basis for approval of Hutruo in the U.S. and EU. If the trial doesn't show that Hutruo is helping patients live longer by a statistically significant margin at the interim peek, Xbiotech will get one more shot when the trial concludes, likely at the end of this year.

Brian Orelli and The Motley Fool have no position in any of the stocks mentioned. The Motley Fool has a disclosure policy.