Pfizer has reported positive data from a Phase II study evaluating PD-0332991 in combination with letrozole in estrogen receptor (ER) positive, human epidermal growth factor receptor 2 (HER2) negative advanced breast cancer patients.
PD-0332991, an investigational, oral and selective inhibitor of the CDK 4 and 6 kinases, plus letrozole significantly improved progression-free survival (PFS) compared with letrozole alone in post-menopausal breast cancer patients.
Pfizer oncology business unit clinical development and medical affairs senior vice president said Dr Mace Rothenberg said the results demonstrated the magnitude of clinical effect and potential of PD-991 as a first-in-class compound.
"Based on these positive Phase II data, Pfizer is planning to open a randomised Phase III study of PD-991 in this patient population in 2013," Rothenberg said.
Median PFS reported in patients administered with the combination of PD-991 plus letrozole was 26.1 months, which was a statistically significant improvement compared to the median PFS in women who received letrozole alone, only 7.5 months.
A 45% objective response was reported in PD-991 plus letrozole group patients, while a 31% objective response was reported in those who received letrozole alone.
The clinical benefit rate was 70% versus 44%, respectively in the study that observed neutropenia, leucopenia, anemia and fatigue treatment-related grade 3/4 adverse events in patients given combination therapy.
Parts one and two of the Phase 2 study are ongoing, while final efficacy and safety data are expected shortly.
Phase II trial lead investigator and Jonsson Comprehensive Cancer Center Revlon/UCLA Women's Cancer Research Program associate professor of medicine Dr Richard Finn said; "The oncology community is looking forward to the further evaluation of PD-991 in the planned Phase III trial and very interested in the potential for this novel CDK 4 and 6 inhibitor to improve the treatment landscape for patients with advanced breast cancer."
Pfizer is also undertaking trials of PD-991 as a treatment for other cancers, including liposarcoma, liver cancer, multiple myeloma andnon-small cell lung cancer.
Image: Pfizer's global headquarters. The company's investigational drug in combination with letrozole demonstrated significant clinical effects in a Phase II breast cancer study. Photo: Courtesy of Jim Henderson.