FILE PHOTO: The logo of Swiss drugmaker Novartis AG is seen at its headquarters in Basel, Switzerland, January 25, 2017. REUTERS/Arnd Wiegmann/File Photo

ZURICH (Reuters) - Novartis AG said its drug Kisqali (ribociclib) received European Union approval as first-line treatment for a tough-to-treat breast cancer, bolstering the Swiss drugmaker’s bid to challenge U.S. rival Pfizer’s Ibrance.

The EU approved Kisqali in combination with an aromatase inhibitor, such as letrozole, for treatment of postmenopausal women with hormone receptor positive, human epidermal growth factor receptor-2 negative (HR+/HER2-) locally advanced or metastatic breast cancer as initial endocrine-based therapy, Novartis said.

The announcement, while expected, underscores Novartis’s push to strengthen an oncology portfolio hurt last year by the patent expiration on blood cancer drug Glivec.

Novartis considers Kisqali to be one of its new medicines with blockbuster potential for annual revenue in the billions of dollars. Pfizer’s rival drug Ibrance hit about $2.1 billion in sales in 2016.

The approval is based on pivotal phase III MONALEESA-2 trial, which showed Kisqali plus letrozole reduced risk of disease progression or death by 43 percent versus letrozole alone.

It follows a positive opinion granted in June by the Committee for Medicinal Products for Human Use (CHMP) of the European Medicines Agency (EMA) and the green light from the U.S. Food and Drug administration (FDA) in March.