That's good news for women over 50, who are the most likely to have cardiovascular problems when taking Herceptin with other cancer drugs. Herceptin is typically taken after standard hormonal treatments and chemotherapy.
Herceptin blocks the growth protein called HER2, which is found in abundance in some breast cancer cells. A study published in today's Nature Medicine shows why this protein is crucial for the heart.Scientists at the Salk Institute in California genetically engineered a generation of mice that stopped making the mouse version of this protein, erB2, but only in the heart. The mice showed signs of cardiomyopathy at one to six months. The muscle cells that pump blood through the heart became less elastic, and they were more sensitive to adriamyacin, a cancer drug linked to cardiac toxicity.
"We knew Herceptin and anthracylines (like adriamyacin) could cause heart problems," says Dr. Lamar McGinnis, senior medical consultant to the American Cancer Society. "But we had no idea how."
The cardiac dangers are not as pronounced for women taking Herceptin alone, researchers say. It's when patients go through several anti-cancer regimens and add new drugs that the risk begins to build.
"If breast cancer patients take Herceptin or anthracyclines by themselves, only 8 percent have problems," says Kuo-Fen Lee, a researcher at the Salk Institute. "If they take them both of them together, that figure goes up to 30 percent. We need to have better control of this situation. It's not worth risking a patient's life until we do."
The Salk study points to ways these drugs can be made safer, however. The next step is to create a pill that promotes contractility in the heart, and which can be taken along with these other drugs. The Salk team is now designing such a drug, and it may be ready within a year.
"Then we can use Herceptin without worrying about its side effects," Lee says.
"This would be great for the older breast cancer patients who are more likely to have cardiovascular problems," McGinnis says. "We're going to see more cases of breast cancer as more women pass the age of 50. And there's a real need for a regimen that works well in this population."
About 30 percent of breast cancer patients respond well to Herceptin. With this new approach, the drug could be more widely used, the Salk researchers note. It also could be used with prostate, lung and ovarian cancers.