LOS ANGELES -- In the first success of an entirely new approach to fighting cancer, scientists have shown they can lengthen the lives of some terminally ill breast cancer patients with a medicine that thwarts the defective genes causing their disease.
Attacking cancer at its genetic roots has been a goal of science for two decades, but researchers said Sunday that this is firm evidence at last they can actually do this.
Experts predict that the new drug, called Herceptin, will come on the market next fall and could quickly become a standard treatment for the one-quarter or more of breast cancer patients whose tumors are driven by multiple copies of a gene called HER-2. It substantially boosts the power of ordinary chemotherapy and carries none of the usual cancer drug side effects, such as nausea and hair loss.
But perhaps even more important, doctors say, is that this treatment works at all, since it shows that one of the hottest areas of cancer research is likely to pay off.
"This proves the paradigm. If we understand what is broken in the malignant cell, we may be able to fix it," said Dr. Dennis Slamon of the University of California, Los Angeles.
Dozens of other drugs in earlier stages of development are aimed at sidestepping a variety of genetic flaws that make tumors grow uncontrollably, and several of these could be available in the next few years.
"This is not the end of the story. It is the beginning of the story," said Dr. Allen S. Lichter of the University of Michigan, incoming president of the American Society of Clinical Oncology.
Results of the first large studies of Herceptin were presented Sunday at the society's annual scientific meeting, attended by about 18,000 cancer specialists.
Doctors tested it on women with invariably fatal advanced breast cancer that had spread to other parts of their bodies. When added to standard treatment, they found it lengthened their lives an average of three months. While this may seem modest, researchers said it represents a major impact in such a late stage of the disease.
Researchers are unsure of the treatment's ultimate impact on survival, but a few cases suggest it could be substantial in those with the HER-2 defect. Typically, such women die within 10 to 18 months after the cancer spreads; however, one of the earliest patients to get Herceptin is still alive after almost six years and another has survived nearly four years.
Researchers predict the results could be much more impressive when the drug is given at earlier stages of the disease before it has moved beyond the breast and lymph nodes.
"There is absolutely no question that there will be a lot of use of this drug once it's available," said Dr. Larry Norton of Memorial Sloan Kettering Cancer Center in New York City, one of the doctors who tested it.
Herceptin is made by Genentech Inc., which financed two studies presented at the conference by Slamon and Dr. Melody Cobleigh of Rush-Presbyterian-St. Luke's Medical Center in Chicago.
The path of scientific discovery began in the 1980s, when Dr. Robert Weinberg of Massachusetts Institute of Technology discovered HER-2. The gene produces a protein on the surface of cells that serves as a receiving point for growth-stimulating hormones.
Twelve years ago, Slamon's team found that about 30 percent of women with breast cancer have many extra copies of this gene. The result: Their breast cells reproduce out of control and spread through their bodies. It is much more aggressive than breast cancer fueled by other genetic flaws.
Scientists reasoned they might reduce HER-2's impact by somehow blocking the extra hormone docking points created by the gene. At Genentech, scientists cloned antibodies designed to do this. One turned out to be Herceptin, the first treatment designed from start to finish to attack a specific genetic error unique to cancer cells.
Researchers tested it on 691 women with spreading breast cancer who carried extra copies of HER-2. Among those who had not been previously treated, doctors compared standard chemotherapy alone to chemo plus Herceptin.
They found that tumors shrank at least 50 percent in half of the women getting Herceptin, compared with one-third taking chemo only. The cancers resumed growing an average of 7.6 months later in the Herceptin patients, but this was three months later than in the other women.
The researchers also tested Herceptin alone in women who had relapsed after standard chemotherapy. In 4 percent the tumors disappeared completely, and they shrank by at least half in another 12 percent.
The drug is given once a week in half-hour infusions. Doctors are still unsure whether the treatment can ever be safely stopped or whether patients will need to take it for the rest of their lives.
Slamon recommended that breast cancer patients ask their doctors to check them for HER-2, since this is not routinely done. Although the drug will not be routinely available until it wins Food and Drug Administration approval, small amounts are distributed through a lottery run by the National Cancer Institute.
Those interested in entering the lottery for Herceptin can obtain information by calling the National Cancer Institute at 800-4-CANCER.