ORLANDO, Fla. -- An experimental therapy designed to block the growth of blood and lymphatic vessels failed to show a significant improvement in progression-free survival of colorectal cancer patients, according to interim trial results presented at the meeting of the American Society of Clinical Oncology.

An interim analysis of phase III data of the VEGF inhibitor PTK/ZK, or vatalanib,, which was developed by


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, failed to show a statistically significant survival benefit, researchers said.

In a trial involving 1,168 patients on Folfox chemotherapy, patients who were additionally treated with PTK/ZK didn't see a meaningful improvement in survival without disease progression. Folfox, a combination therapy, is the most common treatment for colorectal cancer.

Side effects of PTK/ZK included hypertension and thromboembolic events. Researchers said PTK/ZK didn't increase bleeding or bowel perforation when compared with a placebo. The trial is ongoing and final results are expected in the second half of 2006. In its first quarter earnings release last month, Novartis reaffirmed its plans to submit PTK/ZK for regulatory approval in 2007.

On the positive side, the study did show that 40% of patients with a high level of LHD, an enzyme that suggests the presence of tissue damage, did show significantly improved progression-free survival.

In a press release, Novartis added that patients who received the PTK/ZK-Folfox combination had a 17% reduction in risk of disease progression, compared with Folfox alone when assessed by the patients' physicians. Assessment by central review showed a 12% reduction in risk of disease progression, however, the difference did not achieve statistical significance.

"Complete results of the study, including data on survival, will be needed to assess the overall benefit of PTK/ZK as a part of the first line treatment of advanced colorectal cancer," said Dr. J. Randolph Hecht, the lead author of the study.

"The fact that certain specific groups of patients had greater benefit may allow us to find better ways of understanding and using these types of drugs," says Hecht.