Six women in an Avastin breast cancer clinical trial have developed clinical congestive heart failure, prompting enrollment in the study to  be suspended.

According to The Wall Street Journal, the halted Avastin trial was known as E5103. The late-stage trial was testing Avastin in combination with chemotherapy for treatment of early-stage breast cancer.  The trial was one of eight studying Avastin as a treatment for preventing relapse after surgery, known as adjuvant therapy. 

Such studies require careful monitoring, as patients undergoing adjuvant therapy have higher survival rates than those with advanced cancer, the Journal said.  The trial protocol required that enrollment stop if six or more cases of clinical congestive heart failure are seen in the first 200 patients.

Five of the six cases of congestive heart failure were “resolved” after the patients stopped taking both Avastin and the chemotherapy treatment.   There was no information available for the sixth patient, the Journal said, but none of the six have died.

According to the Journal, the trial’s data safety monitoring board will evaluate the data and determine the next steps.  Patients now enrolled in the trial will be able to continue after discussing the developments with their doctor and signing a consent form,  the Journal said.

According to a report on Bloomberg.com, the study was slated to enroll 4,950 patients, and so far 3,439 had joined since November 2007.

Avastin was the first approved therapy designed to inhibit angiogenesis, the process by which new blood vessels develop and carry vital nutrients to a tumor. Avastin was approved by the Food & Drug Administration (FDA) in 2004 to treat metastatic colon cancer, and in 2006, the agency approved it as a treatment for non-small cell lung cancer. Last year, the FDA also approved Avastin as a metastatic breast cancer treatment, and this past May, it was approved to treat glioblastoma multiforme, an incurable brain cancer.