Although researchers have long known that breast cancer doesn't behave the same way in everyone, they've only recently begun to penetrate the disease at a molecular level and appreciate that it's actually many diseases. This new knowledge is beginning to make it possible to match the right therapy with the right patient.
Much of the excitement at the 2005 American Society of Clinical Oncology (ASCO) meeting centered on trastuzumab — better known as Herceptin — a drug designed to act against breast cancer cells that are genetically programmed to make too much of a protein called HER2 (human epidermal growth factor receptor 2). Women whose breast cancers overproduce HER2 are said to be HER2 positive, and they generally have a poor prognosis, even with chemotherapy. About 25% of all breast cancers overexpress HER2.
Herceptin was approved in 1998 for HER2 positive women whose breast cancer has spread (metastasized). The drug doesn't work for everyone, but when it does, the results can be astounding; in some cases, breast tumors have disappeared. This led to trials of Herceptin in newly diagnosed women whose breast cancers are HER2 positive. Results from two such trials were presented at a 2005 ASCO session described by some as "transformational" and "practice-changing."
The data showed that adding Herceptin to standard chemotherapy cut the rate of breast cancer recurrence by 52%, compared to chemotherapy alone. Researchers still don't know whether Herceptin works better when given with chemotherapy or after it. But there's no question that it should now be a first-line therapy — not just a treatment for metastatic disease. One unanswered question is how to manage heart problems, which affect 3%–4% of women who take Herceptin with the chemotherapy drug Adriamycin. It may be that a different chemotherapy regimen can work as well without affecting the heart. A trial testing this idea is underway as of late summer 2005.
Earlier in 2005, researchers involved in another Herceptin study reported that women with early-stage HER2 positive breast cancer did so much better if they received Herceptin plus chemotherapy before surgery that the trial was stopped and revised so that all participants could take advantage of the combined treatment.
For now, a complete and accurate pathology report remains the foundation of treatment planning. That's one reason it's important, whenever possible, to get breast cancer care at a major cancer center, such as those designated by the National Cancer Institute (for a list of locations, phone numbers, and Web sites, see www3.cancer.gov/cancercenters).
November 2005 Update