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Antibody Shrinks Breast Tumors

Artificial antibodies can shrink the tumors of women with advanced breast cancer, researchers announced yesterday at the American Society of Clinical Oncology (ASCO) meeting in Los Angeles. Experts says it's not yet clear whether the therapy can extend patients' lives, but the news suggests renewed promise for these compounds, which suffered disappointing clinical results in the late 1980s.

Antibodies are a first line of the body's natural defenses against infection. Each antibody grasps a specific target and holds on, meanwhile alerting the rest of the immune system to the intruder. Researchers at Genentech designed an artificial antibody to a particular molecule, a receptor for growth factors called HER-2/neu, which is found in abundance on the surface of recalcitrant breast tumors. Numerous studies have shown that the unlucky 25% to 30% of breast cancer patients whose tumors produce more HER-2/neu have worse prognoses.

When the antibody was combined with the chemotherapeutic drug taxol, 42% of 96 women with metastatic breast cancer responded, with tumors shrinking by as much as half. That was much better than the 16% of 92 patients who improved with taxol alone. Addition of the antibody also seems to have extended the time to relapse from 4 months to as much as 11 months. Side effects were minor. "For marginal additional toxicity [to the patient], you get a huge amount of benefit," says Genentech's project leader Robert Cohen.

Breast cancer patients who have exhausted other treatment options are already demanding the antibody, and the FDA has promised consideration within 6 months. "We estimate that 30,000 to 50,000 women would be eligible" to receive prescriptions for Herceptin if it is approved, says Cohen.

Although Herceptin slows disease progression, it is too early to say that it prolongs women's lives, cautions radiation oncologist Alan Lichter of the University of Michigan Medical School in Ann Arbor and president of ASCO. Lichter calls the response "modest," but significant in that it shows that antibody therapies, considered best for blood cancers, can work against solid tumors too.