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Trastuzumab is a specific type of biologic therapy, a monoclonal antibody, designed to shut down activity of these HER2 proteins by sticking to and "smothering" them, halting the pro-growth molecular instructions that these proteins relay into the body of the cancer cells. When approved by the FDA in 1998, trastuzumab helped usher in the era of targeted therapy because it specifically attacks a molecular defect on a cancer cell.
The first use of trastuzumab, however, was in women whose cancer was the most difficult to treat, because it had spread beyond the breast. Still, when used with chemotherapy, trastuzumab reduced tumor size by more than 50 percent, and extended survival, according to investigators who conducted these clinical studies. The best response to trastuzumab was seen in patients with the highest levels of HER2 protein in their tumors, proving the therapy was truly zeroing in on the right molecular target.
Extending benefit to early disease
The clear benefit of adding trastuzumab to chemotherapy for patients with advanced breast cancer, considering its overall tolerability, led several investigators (including Dr. Perez) to develop studies in the late 1990s. Researchers sought to test how the drug would treat HER2-positive cancer before it had a chance to spread. They believed that if the drug could help women with the poorest prognoses, the benefit it could offer women with the earliest stages of invasive, HER2-positive breast cancer might be dramatic. What they found was almost the proverbial magic bullet. In one of four major national studies that examined early use of trastuzumab, they discovered that the drug could change the natural history of the disease. Trastuzumab cut cancer recurrence — the return of the disease by 52 percent, compared to standard therapy, Dr. Perez reported late last year. "That's the largest improvement we've seen in more than 30 years, and perhaps ever in the treatment of breast cancer," she noted at the time results were announced
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