Colorectal Cancer Drug Claims Questioned

Was Xilonix given a positive spin?

Texas-based XBiotech has said that its experimental colorectal cancer treatment Xilonix plus best supportive care improved overall survival compared with placebo and best supportive care in a recent study. Those figures, however, don’t stand up under close scrutiny, analyst Adam Feuerstein writes in The Street.

XBiotech reported that, among responders in both the treatment and placebo arms, “clinical response was associated with a 2.7-fold increase in overall survival (11.5 months vs. 4.2 months in responders vs. nonresponders, respectively).” Feuerstein calls the statement “clinically meaningless sleight of hand.” 

“Claiming patients who respond to a drug are living longer than patients who don't respond is an old data-analysis trick usually attempted by companies when the real survival analysis––drug vs. placebo or control––shows nothing,” he observes.

Feuerstein was also annoyed by Biotech’s statement that “overall survival was not compared between treatment arms because after 8 weeks, all patients were eligible to receive study drug.” 

“In other words,” he writes, “XBiotech claims a credible survival analysis—Xilonix vs. placebo—was impossible to assess because patients randomized to placebo at the start of the trial crossed over to Xilonix after eight weeks.”

“If the company knows ‘responders’ to either Xilonix or a placebo, pooled together, are living an average of 11.5 months, then it’s an easy task to separate them out and report proper survival data,” he adds.

XBiotech also failed to state whether Xilonix was able to shrink tumors or delay tumor growth “even though these endpoints were measured in the phase III study,” Feuersein notes.

XBiotech didn’t respond to questions from The Street about the missing efficacy analyses.

“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,” Feuerstein writes. “But if the messy, confused clinical data disclosed Saturday are any indication, a Xilonix approval in Europe is far from a sure thing.”

According to XBiotech, Xilonix is the first monoclonal antibody to “specifically target and neutralize interleukin-1 alpha (IL-1a), one of the most potent inflammatory signaling molecules.” The IL-1 pathway is believed to be an important target for anticancer therapy because of its potential role in the local and systemic effects of cancer. 

Sources: The Street; July 5, 2016; BioSpace; July 5, 2016; and GlobeNewswire; July 2, 2016.