Shares of the Cambridge, U.K. company were up 1.4% to $57.02 at last check.
The results, which were published in The New England Journal of Medicine, showed that the drug reduced the combined risk of recurrence of cancer or death from any cause by 42% compared with a placebo.
After three years, 85.9% of patients treated with Lynparza remained alive and free of invasive breast cancer and second cancers compared with 77.1% on a placebo.
The treatment also demonstrated a statistically significant and clinically meaningful improvement in the key secondary endpoint of distant disease-free survival in the overall trial population, AstraZeneca said.
Lynparza, which was developed with Merck & Co. (MRK) - Get Report has become one of the company’s top sellers, the Wall Street Journal reported, generating $1.8 billion in sales last year. The treatment carries a U.S. list price of about $14,449 per patient monthly.
The treatment belongs to a class of drugs called PRAP inhibitors that stop cancer cells from repairing themselves after damage from chemotherapy.
Last year, the U.S. Food and Drug Administration had approved Lynparza for patients with advanced prostate cancer.
"By providing a treatment which significantly reduces the risk of breast cancer returning in these high-risk patients, we hope Lynparza will set a new benchmark demonstrating sustained clinical benefit," Dave Fredrickson, executive vice president of the oncology business unit, said in a statement. "We are working with regulatory authorities to bring Lynparza to these patients as quickly as possible."
In April, the U.S. government said it planned to share its unused batch of AstraZeneca's COVID-19 vaccine with foreign countries.
The European Medicines Agency said in April that the drug titan’s COVID vaccine is probably causing deadly blood clots in a small number of vaccinated people.