The company said last week that the relative risk reduction of cancer recurrence was 25.2% and that the results were broadly consistent regardless of patients’ menopausal status or cancer progression status.

The results were presented at the annual meeting of the American Society of Clinical Oncology in Chicago. 

The Novartis treatment has been approved to treat hormone-driven breast cancer that has spread to other parts of the body, where Novartis has taken market share from Pfizer's Ibrance.

But an earlier diagnosis, when tumours can still be surgically removed, is much more common, representing about 90% of patients. 

Still, better drugs are needed after surgery because the cancer later returns in between a third and one half of cases.