Sights set on first targeted therapy for triple-negative breast cancer
An MD Anderson study is seeking new drugs to combat triple-negative breast cancer, an aggressive form of the disease that doesn’t rely on the hormones estrogen and progesterone or the protein HER2, which fuel the growth of most breast cancers.
The project’s goal? Find drugs to combat the cancer, which doesn’t rely on the hormones estrogen and progesterone or the protein HER2, which fuel the growth of most breast cancers.
“Given this, the drugs that treat most breast cancers by blocking their ability to use those three things to survive don’t work on triple-negative breast cancer,” says Stacy Moulder, M.D., associate professor of Breast Medical Oncology and the trial’s principal investigator.
Instead, doctors are left to treat triple-negative patients with traditional chemotherapy drugs, surgery and radiation.
Typically, patients with a triple-negative breast tumor that’s larger than one centimeter and hasn’t spread to other parts of the body are given chemo before surgery. In nearly half of these patients, chemo works well. It kills all or nearly all of the cancer cells, and little to no cancer in the breast or lymph nodes is present at the time of surgery.
“This is associated with an extremely good prognosis,” Moulder says.
But the other half of patients who do not respond well to chemo face a high probability their cancer will come back within three years after treatment. When the disease returns, prognosis is poor.
“This is why triple-negative breast cancer is part of MD Anderson’s Moon Shots Program,” says Debu Tripathy, M.D., chair of Breast Medical Oncology and a collaborator on the trial. “We need drugs that work, and we need them now.”
Only a few years ago, researchers discovered that triple-negative breast cancer isn’t a “one-size-fits-all” disease. Instead, six distinct subtypes have been identified so far, “and more will likely be discovered in the future,” Moulder says.
Within each subtype, tumors have different genetic defects. Therefore, “it stands to reason that each subtype should be treated differently,” says Jennifer Litton, M.D., associate professor of Breast Medical Oncology and a trial collaborator.
Yet the current standard of care is to use the same chemotherapy for all subtypes of the disease.
“This is a very complex group of cancers and they don’t all behave the same way,” Litton says. “To treat these patients we have to gain more knowledge of the molecular events that drive each subtype. Then and only then can we match the right drugs to the right patients.”
Drugs that specifically target a cancer’s genetic abnormality are called targeted therapy or precision medicine. Triple negative is the only form of breast cancer for which there is no targeted therapy, Litton says.
Here’s how it works:
Patients who’ve been advised to start chemo before surgery (those whose tumors haven’t spread and are larger than one centimeter) first have their tumors biopsied. They then can immediately start the first of two sequential chemo regimens.
While patients are undergoing their first round of chemo, a chemo-sensitivity predictor test, developed by MD Anderson professor of Pathology W. Fraser Symmans, M.D., is run on their biopsied tumor samples to determine if their tumors will respond to chemo. If a tumor tests “chemo-sensitive,” the tumor is responding to the chemo. If a tumor tests “chemo insensitive,” the chemo is ineffective.
“You may wonder why patients in this trial are placed on chemo when we don’t yet know if their tumor is chemo sensitive,” Moulder says. “We start chemo immediately so we don’t waste time and allow the cancer to spread. If the chemo-sensitivity test determines that chemo won’t work for a particular patient, we haven’t done any damage and we can adjust their course of treatment.”
During this testing, the tumor’s molecular makeup is also revealed, and the patient’s triple-negative breast cancer subtype is identified.
After completing the first round of chemo, those patients whose tumors are found to be chemo-sensitive are prescribed a second round of standard chemo treatments before undergoing surgery. They need chemo only, not the toxicity of more drugs. In the second round of treatment, patients with chemo-insensitive tumors are placed in clinical trials for targeted drugs that are predicted to work best on their individual tumor’s molecular makeup and subtype, in combination with standard chemo.
Two-thirds of patients enrolled in the study receive the treatment described above. The other third do not receive the results of the molecular testing. All patients are allowed to enter a clinical trial for the second part of their treatment, but only the first group will have the molecular testing results to guide their choice of clinical trial.
“This helps us determine if our new approach of adding a targeted drug based upon the molecular testing results will benefit patients,” Moulder says.
No placebos are used in these trials. Some of the drugs tested already are approved to treat other cancers. Others are new and haven’t yet gained Food and Drug Administration approval. If they perform well and increase the number of patients with minimal or no cancer at the time of surgery, the drugs will enter the path to FDA approval.
“This is personalized medicine at its finest,” Moulder says. “The practice of tailoring drugs and therapies to individuals based on their genes or their cancer’s genes is the way of the future.”
An added benefit, she says, is that genetic testing may identify some tumor abnormalities that until now have been unknown.
“I’m sure there are many more triple-negative subtypes that we don’t yet know about,” she says. “I’m guessing in the next decade we’ll identify 20 or 30 more. The challenge will be to find drugs that work best for each one.”