The new label opens up a significant market opportunity for Lilly, as about 70% of people diagnosed with breast cancer have the hormone receptor positive, HER-2 negative type. The National Cancer Institute estimates there will be more than 280,000 new breast cancer cases in the U.S. this year.

“We think this approval is important and practice changing,” Louise Chen, an analyst at Cantor Fitzgerald, wrote in an Oct. 13 note to investors. Chen said she expects that further analyses of Lilly’s study will eventually show an overall survival benefit for Verzenio as well.

Researchers in Lilly’s study found that patients given Verzenio on top of standard endocrine therapy were at 25% lower risk than those on endocrine therapy alone to have their cancers return after about 15 months of follow-up. Further analysis of the data showed a greater benefit in those patients with higher Ki-67 scores, Lilly said Wednesday.

There had been some question about whether the class of drugs known as CDK 4/6 inhibitors could work for earlier-stage patients. In 2020, Pfizer said its market-leading Ibrance drug failed in a trial similar to Lilly’s. Then two weeks later, Lilly announced positive results for Verzenio.

Ibrance, Verzenio and Novartis’ Kisqali are all approved for patients with advanced cancer whose tumors have started to spread. The drugs work by blocking enzymes that tumors rely on to grow and multiply. Ibrance was the first in the class to win approval, in 2015, and has become a top seller for Pfizer, bringing in sales of $5.4 billion last year.

Before its trial failure in 2020, Pfizer estimated that expanding the use of Ibrance to earlier-stage cancer could double the number of patients eligible for the treatment. Novartis is also eyeing a bigger market for Kisqali, with Phase 3 research underway in earlier-stage patients. Results from that study are due in 2022, according to the Swiss drugmaker.