A new study says that chemotherapy does remove breast tumors, but is useless when it comes to destroying breast cancer stem cells.
Comparing the challenge to eradicating stubborn weeds from a garden, the researchers at Baylor College of Medicine (BCM) in Houston, Texas, said chemotherapy often fails because it leaves behind many of the stem cells that help re-ignite tumors.
"It's not enough to kill the dandelion blossom and stalk that appear above ground," said Michael Lewis, assistant professor of molecular and cellular biology at the BCM Breast Cancer Center. "You have to kill the root beneath the soil as well."
The discovery underscores the need to develop a treatment that can target stem cells in addition to the tumor, Lewis said.
"What we found is that one reason chemotherapy frequently does not work is that you kill the bulk of the tumor but leave many of the stem cells behind," he said.
"It appears that these cells, by their nature, are resistant to the effects of anti-cancer drugs," said Lewis, whose findings appear online in the Journal of the National Cancer Institute.
A cocktail of anti-cancer medicines together with the drug lapatinib appears to kill both the tumor and the stem cells, he said.
The promising drug, still being evaluated, would be used to treat breast cancer that has metastasized and contains the protein marker called HER2.
The Baylor researchers took biopsies from the tumors of patients with and without the HER2 marker before and after different treatments.
In the group of people whose tumors did not carry the HER2 marker, the 31 patients received conventional chemotherapy. While the number of tumors significantly decreased, the proportion of cancer stem cells was greater than before the treatment, the study said.
The other group -- 21 patients with HER2 -- were given lapatinib and two common breast cancer drugs. That group saw a dramatic drop in tumor cells, and the percentage of cancer stem cells remained unchanged or even dropped slightly, the researchers said.
"The tumor shrank dramatically," said Jenny Chang, associate professor of medicine and medical director of the BCM Breast Care Cancer Center.
"But in contrast to treatment with conventional chemotherapy, the relative proportion of stem cells did not go up. This means the stem cells were killed off with the same frequency as the bulk of the tumor. This is the first time this has been demonstrated."