Tanespimycin Shows High Level Of Activity In Breast Cancer Patients

Armen Hareyan's picture
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Kosan Biosciences Incorporated's lead Hsp90 inhibitor, tanespimycin, demonstrated a high level of antitumor activity in a Phase 2 trial when administered in combination with trastuzumab (Herceptin) to patients with HER2-positive metastatic breast cancer whose disease had either progressed after, or did not respond to, treatment with trastuzumab immediately prior to entering the trial. Of 27 evaluable patients, 17 patients showed clinical benefit including 7 patients with partial response (PR), 5 patients with tumor regression (minor response or MR) and 5 patients with extended stable disease (SD, greater than 4 cycles), yielding an overall clinical benefit incidence of 63%. Common toxicities were mainly mild to moderate and included fatigue and gastrointestinal symptoms.

Updated data from the Phase 2 trial were presented in a poster titled, "Phase 2 trial of the Hsp90 inhibitor tanespimycin (Tan) + trastuzumab (T) in patients (pts) with HER2-positive metastatic breast cancer (MBC)," by Shanu Modi, M.D., of Memorial Sloan-Kettering Cancer Center, at the 44th American Society of Clinical Oncology (ASCO) Annual Meeting being held in Chicago, IL.

"The response data from this Phase 2 trial of tanespimycin plus trastuzumab have grown stronger as more patients have been treated, underscoring our observation that tanespimycin is a highly active and tolerable agent in patients whose disease is refractory to trastuzumab," said Clifford A. Hudis, M.D., Chief, Breast Cancer Medicine Service, Memorial Sloan-Kettering Cancer Center, and senior author on the poster. "We look forward to seeing tanespimycin advance into its next set of clinical trials with the goal of elucidating its potential role in the metastatic breast cancer treatment paradigm."

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"Tanespimycin is the most advanced Hsp90 inhibitor in development for HER2-positive breast cancer and has generated what we believe is highly promising data in this indication," said Pamela Cohen, M.D., Kosan's Chief Medical Officer. "We believe that Hsp90 inhibition is among the most novel and broadly applicable anticancer targets being explored today, and that it may have broad applicability in breast cancer and other cancer indications."

Phase 2 Tanespimycin Data

Tanespimycin is an Hsp90 inhibitor that has demonstrated the potential to disrupt the activity of multiple oncogenes and cell signaling pathways implicated in tumor growth, including HER2, a key pathway in breast cancer.

The objective of the Phase 2 trial is to determine the objective response rate by RECIST in patients with HER2-positive metastatic breast cancer. To be eligible for the trial, patients must have had either progressive disease within 3 months following last dose of adjuvant treatment with trastuzumab or have progressive disease following initial therapy for metastatic disease with trastuzumab (trastuzumab may have been administered with cytotoxic chemotherapy or as a single agent). Tanespimycin was administered at a dose of 450 mg/m2 following administration of the standard dose of trastuzumab.

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