Pfizer has reported encouraging phase II data suggesting its breast cancer candidate PD-0332991 can extend progression-free survival (PFS) by 18 months compared to standard therapy.
PD-0332991 is a cyclin D kinase 4/6 inhibitor and was tested alongside Novartis’ anti-oestrogen drug Femara (letrozole) as first-line treatment for 165 post-menopausal women with oestrogen receptor-positive, HER2-negative locally advanced or metastatic breast cancer.
Women on the combination of PD-0332991 and Femara had a median PFS of 21.6 months, compared with just 7.5 months for those given Femara alone, according to the investigators of the study, who presented the data at the San Antonio Breast Cancer Symposium this week.
Objective response rates were reported at 45 per cent with the combination therapy, versus 31 per cent for Femara, and clinical benefit was seen in 70 per cent and 44 per cent of patients, respectively.
“These results are especially important because of the magnitude of clinical effect observed and the fact that PD-991 represents a potential first-in-class compound,” said Mace Rothenburg, senior vice president of clinical development and medical affairs for Pfizer’s oncology business unit.
PD-0332991 is currently in the lead in the cyclin D kinase inhibitor class and has the potential to be a blockbuster if the impressive results in phase II transfer to pivotal trials, according to analysts at Citigroup. Other companies developing drugs in the class include Eli Lilly and Novartis.
Pfizer’s drug could find an important role in the 60 per cent of women with breast cancer whose tumours are oestrogen receptor-positive but HER2-negative, making them unsuitable for therapy with HER2-targetting drugs such as Roche’s Herceptin (trastuzumab).
Peak sales of the drug could reach $5bn if the drug demonstrates efficacy in multiple tumour types, according to Citigroup.
Pfizer said it will start a phase III programme in breast cancer in 2013, adding that it already has earlier stage studies of PD-033299 ongoing in late-line metastatic breast cancer, non-small cell lung, liver and ovarian cancers, as well as multiple myeloma and mantle cell lymphoma.