Shares of Gilead took a hit as the stock fell more than 10% on Monday following disappointing results from a late-stage trial of its key lung cancer drug, Trodelvy. The trial failed to significantly extend the lives of patients with a certain type of lung cancer, dealing a blow to Gilead’s ambitions in the cancer treatment space.

Trodelvy, a leading cancer drug for Gilead, contributed around a third of its $769 million in oncology sales during the third quarter. The phase-three study aimed to expand the use of Trodelvy, which is already approved for treating specific breast and bladder cancers.

While patients with advanced or metastatic non-small cell lung cancer who received Trodelvy lived longer than those who underwent chemotherapy alone, the results did not meet the trial’s success criteria. Gilead plans to discuss the results with regulators to assess whether certain lung cancer patients may still benefit from the drug.

Trodelvy falls under the category of antibody-drug conjugates (ADCs), a sought-after class of treatments that deliver targeted cancer therapy to minimize damage to healthy cells. This contrasts with standard chemotherapy, which is less selective and can impact both cancerous and healthy cells.

Jefferies analyst Michael Yee noted that the trial results were not entirely surprising, given the mixed data from early studies and the underwhelming performance of competing drugs. He also highlighted that the results could impact investor confidence in Gilead’s potential oncology sales.