Pfizer says it has completed the submission of a New Drug Application to US regulators for its breast cancer drug palbociclib.

The drugs giant is hoping to get approval from the US Food and Drug Administration for palbociclib, in combination with the aromatase inhibitor letrozole, for the treatment of postmenopausal women with oestrogen receptor positive (ER+), human epidermal growth factor receptor 2 negative (HER2-) advanced breast cancer who have not received previous systemic treatment for their advanced disease.

The submission is based on the final results of PALOMA-1, a Phase II trial comparing palbociclib plus letrozole versus the latter alone in this population of patients. The Pfizer drug received breakthrough therapy designation from the FDA in April 2013 based on interim data from the mid-stage study which showed a statistically significant improvement in median progression free survival compared to letrozole alone (26.1 months versus 7.5 months).

The FDA has a 60-day filing review period to determine whether the NDA is acceptable for filing. Palbociclib selectively inhibits cyclin-dependent kinases (CDKs) 4 and 6 to regain cell cycle control and block tumour cell proliferation.