(Bloomberg) -- Gilead Sciences Inc.’s Trodelvy delayed progression of a common type of advanced breast cancer by 1.5 months in a study, a modest but statistically significant improvement that may help expand use of the medicine.

The drug is already approved for an uncommon type of breast cancer called triple negative, but Gilead is now targeting the much larger group of hormone-positive breast cancer patients who have failed other therapies. The data are being presented at the American Society of Clinical Oncology meeting on Saturday.

Preliminary survival findings from the study suggested a benefit for Trodelvy but didn’t meet the threshold for statistical significance. There were no unexpected new side effects.

It isn’t clear whether regulators in the U.S. or elsewhere will want to wait for final survival data from the study before deciding whether to allow broader use of the medicine. In an interview, Gilead Chief Executive Officer Daniel O’Day said the company would start discussing the results with regulators as soon as the cancer meeting ends next week. 

“We have very strong results to go forward and have these discussions,” said O’Day. 

Cancer drugs are key for Gilead’s growth as it tries to move beyond its mature antiviral business. But some analysts have questioned whether Trodelvy will be able to show a clinically meaningful benefit in the broader group of breast patients.

Jennifer Litton, a breast cancer oncologist at MD Anderson Cancer Center who wasn’t involved with the study, said proving survival differences is difficult in advanced breast cancer. She thinks the Gilead drug could “provide another option” for patients. 

Gilead acquired Trodelvy in 2020 through its $21 billion purchase of Immunomedics Inc. This April, the company took a $2.7 billion impairment charge related to the acquisition, an acknowledgment that the drug wasn’t paying off as quickly as it had once hoped.

In the interview, O’Day said that he stands by his assessment of Trodelvy at the time of the deal, calling it “a pipeline in a product” that could have a wide variety of uses.

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