Puma Biotechnology Inc. (NYSE:PBYI) fell $19.37 (25%) to $57.06 on Monday on Phase II data for the company's neratinib (PB272) for HER2-positive breast cancer in patients with brain metastases and concerns about prospects of neratinib as an adjuvant treatment of HER2-positive breast cancer. In the Phase II TBCRC 022 trial, once-daily oral neratinib led to three partial responses in a cohort of 40 HER2-positive breast cancer patients with brain metastases. There were four cases of stable disease for six months or greater and 12 cases of stable disease for less than six months. Median progression-free survival (PFS) was 1.9 months and median overall survival (OS) was 8.7 months. All patients had received prior radiotherapy.
Data were presented at the American Society of Clinical Oncology meeting in Chicago. The trial, which was sponsored by the Dana-Farber Cancer Institute, is enrolling two additional cohorts of HER2-positive breast cancer patients with brain metastases.
Investors may also have been concerned that the failed Phase III ALTTO trial of two marketed HER inhibitors makes it unlikely neratinib will succeed as an adjuvant treatment of HER2-positive breast cancer (see below).
Neratinib, an oral inhibitor of HER1, HER2 and HER4 kinases, is also in Phase III testing as third-line treatment of HER2-positive metastatic breast cancer and Phase II testing in patients with solid tumors who have an activating HER2 mutation. Additionally, neratinib will be included in the Phase III I-SPY 3 trial for the neoadjuvant treatment of breast cancer, which is slated to start this year. Puma has exclusive, worldwide rights to develop and commercialize the compound from Pfizer Inc. (NYSE:PFE).
http://www.biocentury.com/dailynews/clinical/2014-06-02/adjuvant-tykerb-herceptin-miss-in-phase-iii-altto-trial
Adjuvant treatment of HER2-positive early breast cancer with oral Tykerb lapatinib from GlaxoSmithKline plc (LSE:GSK; NYSE:GSK) plus IV Herceptin trastuzumab from Roche (SIX:ROG; OTCQX:RHHBY) and its Genentech Inc. unit missed the primary endpoint of improving disease-free survival (DFS) vs. Herceptin alone in the Phase III ALTTO trial. Adjuvant treatment with Tykerb plus Herceptin led to a four-year DFS rate of 88% vs. 86% for Herceptin alone (p=0.048). The primary endpoint was designed to test for superiority of Tykerb plus Herceptin vs. Herceptin alone with a p-value of 0.025 or less.
ALTTO was sponsored by GSK and conducted in collaboration with NIH's National Cancer Institute, the North Central Cancer Treatment Group and the Breast International Group. The open-label, international trial enrolled 8,381 patients with HER2-positive early breast cancer. Data were presented at the American Society of Clinical Oncology meeting in Chicago.
Herceptin is a humanized mAb against HER2. Tykerb is a HER1 and HER2 kinase inhibitor. 
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