The company said that tanespimycin is clearly active in patients who are refractory to trastuzumab and whose disease progressed prior to entering the study. Of 20 evaluable patients, 11 patients benefited from activity, yielding an overall clinical benefit incidence of 55%, including five patients with confirmed partial responses, two patients with minor responses and four patients with extended stable disease. Common toxicities were mainly mild to moderate and included fatigue and gastrointestinal symptoms.
Robert Johnson, Jr, Kosan’s president and CEO, said: “The data in this Phase II trial continue to strengthen as we have added patients. We believe that tanespimycin is highly active in patients with HER2-positive metastatic breast cancer who have progressed on trastuzumab, and that this drug candidate’s overall profile is attractive. We intend to complete this Phase II trial and embark upon next steps to explore tanespimycin’s therapeutic potential in breast cancer.”