Merck stock spiked nearly 4% in early Monday trading, a gain of nearly $5.75 billion in market value, as investors cheered another victory for the drug giant’s flagship cancer immunotherapy in treating lung cancer. Investigators reported Monday morning that the late-stage trial, KEYNOTE-o42, showed that taking Keytruda alone for lung cancer had significant advantages over taking chemotherapy alone to treat the deadly disease.

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Depending on just how strong the data is (the full number set won’t be released publicly for a bit), that means that patients could potentially bypass chemo and take Keytruda alone, assuming the Food and Drug Administration (FDA) is on board—an option that could be attractive for lung cancer sufferers who don’t want to deal with the serious side effects of chemotherapy.

Biotech analysts and investors noted the wide-ranging nature of Keytruda’s trial victory, which could expand its existing advantage in the lucrative lung cancer treatment space over rivals like Bristol-Myers Squibb’s (BMS) Opdivo. The Merck drug reportedly hit its survival extension goals in patients with all kinds of levels of “PD-L1,” the protein type targeted by treatments like Keytruda and Opdivo. Bristol-Myers wasn’t able to clear a similar bar in its Opdivo lung cancer trials.

Amazing how KEYNOTE-042 succeeded in the entire > 1% cohort that Bristol failed in years ago. Keytruda is king.

— Brad Loncar (@bradloncar) April 9, 2018

There’s a reason companies like Merck, BMS, and AstraZeneca are attempting to outshine each other in lung cancer immunotherapy: lung cancer is the second most commonly diagnosed cancer in the U.S. It’s also the deadliest, killing nearly 156,000 Americans each year. Keytruda rang in more than $3.8 billion in 2017 sales for Merck, the same year the FDA approved it as a go-to, first-in-line option for advanced lung cancer patients that haven’t received other treatments when combined with chemotherapy. Down the line, it’s possible even that combination with chemo won’t be necessary.