A widely prescribed cancer drug noted for its ability to choke off blood vessels that help tumors grow can cause significant kidney damage in some patients, a team of Long Island scientists has found.

Kidney problems are the second serious condition linked to Avastin and pinpointed in research conducted by Dr. Shenghong Wu and colleagues at Stony Brook University Medical Center. Last year Wu and his team found some patients on the drug were at elevated risk of intestinal perforations.

"This is a drug we use clinically for a lot of tumors - lung cancer, kidney cancer, breast cancer," Wu said in an interview. "The safety is something we are researching. But this drug is used successfully and that is why we are studying it."

Reporting in this month's issue of the Journal of the American Society of Nephrology, Wu wrote that patients on Avastin were at increased risk of severe protein loss from the kidneys, which can lead to permanent damage. Overall, patients on Avastin were at a fourfold risk for protein loss and kidney damage, depending on dosage and the type of cancer.

In terms of incidence, 10 percent of patients being treated with the drug for kidney cancer suffered organ damage and were at highest risk.

Avastin is a product of California-based biotech giant Genentech and was approved in 2004. It joined a burgeoning class of cancer drugs known as "targeted therapies" because unlike broad-spectrum chemotherapy, which attacks all cells, targeted drugs zero in on the cancer-causing mechanism, leaving healthy cells unscathed.

Avastin blunts the growth of tumor blood vessels, which allow the cancer to draw nutrients from the host's blood.

It's also used to treat patients with eye conditions such as macular degeneration and diabetic retinopathy. When injected directly into the eyes it destroys errant blood vessels that damage vision.

But for cancer patients, Avastin - which can cost as much as $50,000 a year - already carries a so-called black-box warning from the U.S. Food and Drug Administration, the agency's highest level of caution because of problems that emerged after its approval, experts said. The drug can cause hemorrhaging in some patients and seriously interferes with wound healing in those who've undergone surgery.

Wu, however, is among the many doctors who strongly defends Avastin's use. "We don't think it's a bad drug because it helps patients control cancer," he said.

Dr. Neil Segal, a cancer specialist at Memorial Sloan-Kettering Cancer Center in Manhattan, agrees the medication's benefits outweigh its risks. "Avastin when added to certain chemotherapies can help many patients.

"These are potential side effects," he said of problems uncovered in Wu's research. "Clinicians need to be aware of them and recognize them if they occur."

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