(RxWiki News) Herceptin (trastuzumab) is a leading medication used to treat a particularly aggressive form of breast cancer, known as HER2-positive. Researchers are now suggesting the medicine may be useful in treating other forms of breast cancer.
An increasing body of evidence finds that cancer stem cells play a key role in the recurrence and spread of cancer. A new study has learned that HER2 appears in small quantities in cancer stem cells of breast cancers that would normally be described as HER2-negative.
Analyzing old data, researchers in previous studies uncovered that Herceptin benefited women whose cancer was mistakenly described as HER2-positive.
These findings, along with new research, suggest that Herceptin may be helpful in treating not just HER2-positive tumors; the medication may keep other forms of breast cancer from spreading.
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HER2 is a protein that promotes cancer cell growth. When this protein is present at high levels, the tumor is classified as HER2-positive breast cancer. About 20 percent of breast cancers are HER2-positive.
Currently, patients with HER2-negative breast cancer are not advised to take Herceptin.
University of Michigan Comprehensive Cancer Center researchers worked with breast cancer cell lines, mouse models, as well as with primary and metastatic human breast cancer samples to study the impact of using Herceptin on HER2-negative tumor cells.
Study author, Max S. Wicha, MD, distinguished professor of oncology and director of the U-M Comprehensive Cancer Center, said in a press release, “We now provide a molecular explanation for the surprising finding that adjuvant Herceptin benefited some women with HER2-negative breast cancer. If this is confirmed in clinical trials, it could alter our approach to breast cancer treatment.”
Adam Brufsky, MD, PhD, professor of medicine at the University of Pittsburgh School of Medicine, told dailyRx News, "This is something we have known about for some time, and it is nice to have some supporting evidence of this effect. We may have to reassess how we determine who benefits from Herceptin and who does not,” Dr. Brufsky said.
Researchers explained that HER2 is seen in the cancer stem cells of various types of breast cancer. Stem cells, which fuel cancer growth and don’t respond to traditional chemotherapy or radiation, make up about 1-5 percent of all the cells in a tumor. Herceptin was able to effectively target and disable the stem cells that expressed HER2.
The investigators also discovered that HER2 levels were higher in bone metastases than in original tumors classified as HER2-negative. Breast cancer most often spreads (metastasizes) to the bone.
Herceptin halted tumor growth in mice with small bone lesions called “micrometastases.” The drug was not effective with established metastatic tumors, however.
The authors contend that these findings open the doors to a whole new approach for treating breast cancer. In addition to chemotherapy to shrink the tumor, additional therapy is needed to attack cancer stem cells responsible for the disease returning.
“The idea of using drugs that cause tumors to shrink, which has been the accepted paradigm for developing therapies, is flawed,” Dr. Wiccha said. “Our work suggests that adjuvant therapies will need to target the cancer stem cell population. Eliminating cancer stem cells by effective adjuvant therapies should prevent tumor recurrence, ultimately resulting in more cures.”
A large randomized clinical trial sponsored by the National Institutes of Health is now recruiting participants at U-M and other sites across the country to further study this theory.
Patients whose tumors are not considered HER2-positive by classic testing should not receive Herceptin outside of this trial.
For information about the trial, call the U-M Cancer AnswerLine at 800-865-1125.
Findings from the current study were published February 26 in the journal Cancer Research.
The study was funded by the National Cancer Institute; Breast Cancer Research Foundation; Komen for the Cure; Taubman Institute at the University of Michigan; Fashion Footwear Charitable Foundation of New York/QVC Presents Shoes-On-Sale and Stand Up to Cancer.
Max Wicha has financial holdings in OncoMed Pharmaceuticals, receives support from Dompe and MedImmune and serves on the scientific advisory board of Veristem; Hasan Korkaya receives research support from MedImmune; Daniel Hayes has received research support from Pfizer, Novartis and Veridex and holds stock options for his role on the scientific advisory board for OncImmune.