Approval of Keytruda in this setting comes about six months after Merck revealed early results from a study called Keynote-564, which showed the immunotherapy could help keep kidney cancers in remission for longer.

The benefit was assessed on a measure known as disease-free survival, or the time until a patient dies or their cancer recurs or metastasizes. As patients are being treated early, when their tumors are still small or local enough to be removed surgically, they typically live for much longer than when tumors are already advanced or metastatic. That means studies must run for longer to prove drugs being tested actually extend patient’s lives, rather than just lengthening the amount of time in remission.

Measuring disease-free survival gives drugmakers a chance to show their drugs have an effect earlier, although the endpoint is criticized by some for overselling a treatment’s benefit.

When Keynote-564 was reviewed to assess Keytruda’s benefit on disease-free survival, only 5% of the study’s nearly 1,000 participants had died, too few to make any determinations about whether the drug extended overall survival, too. The trial will continue to assess overall survival, Merck said in a statement on the FDA’s approval Thursday.

Merck and other drugmakers like Bristol Myers Squibb and Roche are also studying their immunotherapies as adjuvant treatments for other cancer types like skin, lung and breast tumors. Already top-sellers, the drugs could become even more lucrative for their makers should they be adopted widely alongside surgery.

While Keytruda is the first in kidney cancer, results are also expected from studies of Roche’s Tecentriq, Bristol Myers’ Opdivo and AstraZeneca’s Imfinzi.

The FDA approved Keytruda for this setting under priority review, which expedites the regulator’s evaluation.