Gritstone shares fall on shaky study results for colorectal cancer vaccine colorectal cancer vaccine

2024-04-02

疫苗临床3期临床结果免疫疗法

Dive Brief:

Gritstone Bio on Monday said a personalized cancer vaccine it’s developing showed potential in people with colorectal tumors, but the data released by the company aren’t strong enough to prove the treatment works.

Preliminary study results suggest what Gritstone described as an ”early trend” in benefit, appearing to lessen the risk of progression in participants who received the shot alongside immunotherapy and chemotherapy compared to those who didn't.

But that finding wasn’t statistically conclusive and, importantly, a biological marker used to assess treatment response was “uninformative,” the company said. Shares in Gritstone lost nearly half of their value in Tuesday morning trading.

Dive Insight:

While cancer vaccines have historically disappointed in clinical testing, there’s newfound momentum for the field as newer technologies yield stronger signs of potential.

Like a handful of others, Gritstone is developing so-called neoantigen cancer vaccines — personalized shots that are engineered to target proteins specific to a patient’s tumor. Several have produced encouraging results, most notably a melanoma vaccine Moderna and Merck & Co. are testing in a Phase 3 trial.

Gritstone is going after solid tumors that are difficult to treat with immunotherapy, like a type of advanced colorectal cancer known as “microsatellite stable.” The company hopes to show that its shot, when administered as a maintenance therapy, can spur better responses than other treatments.

In pursuit of that goal, Gritstone aims to link its vaccine to reductions in the amount of tumor genetic material circulating in the blood, known as circulating tumor DNA, or ctDNA. Executives previously discussed the possibility of seeking an accelerated approval if the ctDNA results from the company’s ongoing study were strong enough.

The data disclosed Monday falls short, however. In a February research note, ISI Evercore analyst Jon Miller set a benchmark of at least a 25% difference in ctDNA responses — defined as a reduction of 30% or more in ctDNA levels — between trial volunteers who received the shot, and those who didn’t.

Instead, Gritstone found higher response rates in the control arm, a result it blamed on unanticipated effects of chemotherapy. “We simply got it wrong,” said CEO Andrew Allen, in a statement.

Treatment responses defined by changes in ctDNA was the primary endpoint of the study’s Phase 2 portion.

Gritstone pointed to a numeral benefit on tumor progression, but the difference between groups wasn’t statistically significant and the data are not yet mature. A slide presentation visualizing the data showed little difference between graph curves representing the two study arms.

Gritstone said longer follow-up should yield a clearer picture and will present more “mature” data from the trial in the third quarter. It plans to discuss the goal for Phase 3 testing with regulators afterwards.

The company is pressed for cash, though. Gritstone had about $90 million in the bank at the end of September and laid off staff last month. It priced an secondary stock offering shortly announcing the results, raising about $33 million.

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