The phase III Monaleesa-2 study showed superior PFS with LEE011 plus letrozole in pre-defined patient subgroups, from de novo to bone, liver and lung metastases, compared to letrozole alone.
The combination reduced risk of progression or death by 55% over letrozole alone in de novo patients, and by 54% in patients with three or more metastases.
The 12-month PFS rate was 82% in the LEE011 plus letrozole arm compared to 66% with letrozole alone.
In HR+/HER2- breast cancer patients with visceral metastases or bone-only disease, treatment with the combination reduced the risk of disease progression or death by 47% in subjects with visceral metastases and 31% in those with bone-only disease.
Currently, the study is evaluating secondary endpoints, which also includes the patients’ overall survival.
Novartis Oncology CEO Bruno Strigini said: "These additional results from the Monaleesa-2 study are very promising for women with HR+ advanced breast cancer.
"We believe LEE011 could significantly benefit a broad range of women as an initial treatment for metastatic breast cancer and look forward to working with global health authorities to bring this new treatment to patients."
LEE011 is a selective cyclin dependent kinase inhibitor, a class of drugs that help slow the cancer progression by inhibiting two proteins known as cyclin dependent kinase 4 and 6.
The US Food and Drug Administration granted LEE011 breakthrough therapy designation in August this year and priority review in October.