Pfizer Presents Phase 2 Data Showing Investigational Therapy PD-0332991 Plus Letrozole Significantly Improved Progression Free Survival Compared With Letrozole Alone In Patients With ER Positive, HER2 Negative Advanced Breast Cancer

Pfizer Inc. today announced randomized Phase 2 data that showed PD-0332991 (PD-991) in combination with letrozole significantly extended progression free survival (PFS) compared with letrozole alone in post-menopausal patients with estrogen receptor positive (ER+), human epidermal growth factor receptor 2 negative (HER2-) locally advanced or metastatic breast cancer. For patients treated with the combination of PD-991 plus letrozole, median PFS was 26.1 months, a statistically significant improvement compared to the median PFS in women who received letrozole alone, which was 7.5 months (HR=0.37 [95% CI: 0.21, 0.63]; P <0.001). These data were presented today and featured in a press conference at the 35 ^th Annual San Antonio Breast Cancer Symposium (Abstract #S1-6).

“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. Based on these positive Phase 2 data, Pfizer is planning to open a randomized Phase 3 study of PD-991 in this patient population in 2013,” said Dr. Mace Rothenberg, senior vice president of clinical development and medical affairs for Pfizer’s Oncology Business Unit. “We are working with regulatory authorities to advance the development of this promising compound in the most expeditious and responsible way.”

Breast cancer is the most commonly diagnosed cancer ¹ and the leading cause of cancer death among women worldwide. ² Estrogen receptor positive, HER2- breast cancer represents approximately 60 percent of all cases of breast cancer. ³ Despite currently available treatments, survival rates for advanced or metastatic breast cancer remain low. ⁴

About the Phase 2 Program

The focus of Phase 2 evaluation of PD-991 was to measure the clinical activity of PD-991 in combination with letrozole versus letrozole alone in post-menopausal women with ER+, HER2- locally advanced or metastatic breast cancer. In Part 1, 66 patients were enrolled. Preliminary results were presented in May 2012 at the IMPAKT Breast Cancer Conference in Brussels, Belgium, and showed statistically significant improvement in median PFS in the PD-991 plus letrozole arm versus the letrozole arm. Part 2 enrolled 99 additional patients whose tumors were selected for presence of biomarkers: cyclin D1 amplification and/or p16 loss. The results presented here at SABCS reflect the combined interim data analysis of parts 1 and 2 of the Phase 2 evaluation.

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