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.
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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.
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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.
