Herceptin (chemical name: trastuzumab) is a targeted therapy medicine used to treat HER2-positive breast cancer.
A very early study done in mice suggests that Herceptin may effectively treat very small breast cancer tumors in bones, even though the original cancer was classified as HER2-negative.
The study was published online on Feb. 26, 2013 by the journal Cancer Research. Read the abstract of “HER2 Drives Luminal Breast Cancer Stem Cells in the Absence of HER2 Amplification: Implications for Efficacy of Adjuvant Trastuzumab.”
HER2-positive breast cancers make too much of the HER2 protein. The HER2 protein sits on the surface of cancer cells and receives signals that tell the cancer to grow and spread. About one out of every four breast cancers is HER2-positive. HER2-positive breast cancers tend to be more aggressive and harder to treat than HER2-negative breast cancers.
Herceptin works by attaching to the HER2 protein and blocking it from receiving growth signals.
Herceptin, which is given intravenously, is approved by the U.S. Food and Drug Administration to:
- treat advanced-stage, HER2-positive breast cancers
- lower the risk of recurrence (the cancer coming back) of early-stage, HER2-positive breast cancers with a high risk of recurrence
In this study, the researchers analyzed information that was collected as part of an earlier study on HER2-positive breast cancer. They found that some of the breast cancers in the study were incorrectly classified as HER2-positive. Because of this, the cancers were treated with Herceptin even though they were really HER2-negative. The researchers were intrigued because these women got just as many benefits from Herceptin as women diagnosed with actual HER2-positive breast cancer.
In earlier studies, the researchers discovered that the cancer stem cells of many HER2-negative breast cancers are actually HER2-positive. Because the stem cells make up such a small number of cells in a cancer tumor, the amount of HER2 isn’t enough for a test to classify the tumor as HER2-positive.
Breast cancer stem cells are sometimes called “mother” cells – they make other breast cancer stem cells and regular breast cancer cells. Breast cancer stem cells make up about 1% to 5% of all cells in a breast cancer tumor.
The researchers also found that for breast cancers classified as HER2-negative that had spread (metastasized) to the bones, HER2 levels were higher in the bone metastases compared to the primary cancer in the breast.
So in the lab, the researchers bred mice with HER2-negative breast cancer that had spread to their bones and then treated them with Herceptin. They found that Herceptin effectively treated these bone lesions if given early, when the lesions were very small. Doctors call these small lesions “micrometastases.” Herceptin almost completely stopped the very small bone lesions from growing. If Herceptin was given later, after the bone lesions had grown, the medicine offered little benefit.
While encouraging, it’s important to know that these results are very early results, done on mice in a lab. Right now, women diagnosed with HER2-negative breast cancer aren’t advised to take Herceptin. More research is needed before doctors fully understand how Herceptin might be used to treat HER2-negative breast cancer.
A large, randomized study sponsored by the National Institutes of Health is looking this question of how Herceptin may be used to treat HER2-negative breast cancer. If you’re interested in participating, call 1-800-865-1125 to get more information about the study.
You also can visit the Breastcancer.org Clinical Trials pages for more information.