ASCO: Merck's Keytruda doubles time to disease progression in certain colorectal cancer patients

Keytruda kept cancer at bay for 16.5 months in previously untreated patients with microsatellite instability-high or mismatch repair deficient colorectal cancer. (Merck)

The results are out, and they’re practice-changing: Merck’s Keytruda can double the time to disease worsening in patients with certain types of colorectal cancer.

The immuno-oncology star kept cancer at bay for 16.5 months in previously untreated patients with microsatellite instability-high (MSI-H) or mismatch repair deficient (dMMR) colorectal cancer that had either spread to other parts of the body or couldn’t be surgically removed, Merck said ahead of the American Society of Clinical Oncology’s (ASCO) virtual annual meeting.

That’s compared with 8.2 months for chemo, delivered with or without other targeted therapy—meaning Keytruda cut the risk of disease worsening or death by 40%. Investigators had their pick of chemo cocktails, with a popular combination of Roche’s Avastin and a regimen known as mFOLFOX6 among them.

"That's a pretty significant improvement," particularly in what's so far has been an "incurable disease" in the majority of metastatic patients, said Jonathan Cheng. M.D., vice president of oncology clinical development at Merck Research Laboratories.

"To be able to live progression-free—or with your disease—rather than succumb to your disease, I think is an important endpoint and important to patients," he added.

RELATED: Merck looks for leg up on BMS with Keytruda's latest colorectal cancer win

Keytruda not only kept cancer away longer, but also in a larger proportion of patients. At the 12-month mark, 55.3% of patients on the Merck drug hadn’t seen their cancer worsen, versus just 37.3% of chemo patients. And at the 24-month mark, that difference was more pronounced, with cancer still at bay in 48.3% of Keytruda patients and 18.6% of chemo patients.

Eleven percent of Keytruda patients saw their cancer vanish completely, compared with 3.9% of chemo patients. And 83% of those who responded to Keytruda saw their benefits last more than two years, versus just 35% of those who responded to chemo.

“These long-awaited trial results will change clinical practice,” lead study author Thierry André, M.D., said in a statement.

The new data should bring Keytruda earlier into treatment for the 5% of metastatic colorectal cancer patients with MSI-H tumors, which has been "a tough patient population" to treat.

"We desperately wanted treatment options for this patient population," Cheng said, noting that chemo has demonstrated effectiveness, but not durability.

The results should also vault Keytruda further ahead of its competition—Bristol Myers Squibb’s Opdivo—in the colorectal cancer arena. Right now, thanks to a 2017 go-ahead, Keytruda is cleared for previously treated patients with MSI-H tumors, no matter where they're located within the body.

BMS has a green light in the second-line setting that’s more limited than Merck’s, pertaining specifically to MSI-H or dMMR colorectal cancer rather than all MSI-H or dMMR tumors. But, so far, it has no indication for previously untreated patients.

RELATED: Bristol Myers Squibb eyes lead in rare colorectal cancer with new Opdivo results

That's not to say BMS isn't working on it, though. The New York drugmaker trumpeted phase 2 data back in October 2018 showing its Opdivo-Yervoy duo could spur responses in 60% of front-line MSI-H or dMMR colorectal cancer patients.