ZURICH, Aug 3 (Reuters) - Novartis AG breast cancer pill LEE011 has won breakthrough therapy designation from U.S. regulators as a first-line treatment for a form of advanced breast cancer, the Swiss drugmaker said on Wednesday.

The Food and Drug Administration granted the designation to LEE011 in combination with letrozole for treating hormone receptor positive, human epidermal growth factor receptor 2-negative (HR+/HER2-) advanced or metastatic breast cancer.

The designation aims to expedite the development and review of potential new medicines that treat serious or life-threatening conditions.

Clinical trial testing of the pill was stopped early because of good results, boosting Novartis's efforts to build up its oncology business and putting it on track to compete with a similar blockbuster product from Pfizer.

(Reporting by Michael Shields)