Washington, Apr 30 : Researchers from Baylor College of Medicine in Houston have revealed though conventional anti-cancer drugs kill breast cancer tumours they leave behind many of the breast cancer stem cells that lead to cancer relapse.
The study led by Dr. Michael Lewis, assistant professor of molecular and cellular biology and a faculty member in the Lester and Sue Smith Breast Cancer Centre at BCM suggests that eradicating these stem cells can help controlling breast cancer progression.
"What we found is that one reason chemotherapy frequently does not work is that you kill the bulk of the tumour but leave many of the stem cells behind," said Lewis.
"It appears that these cells, by their nature, are resistant to the effects of anti-cancer drugs," he added.
However, Lewis added, treatment with the drug lapatinib and anti-cancer drugs appears to kill both the tumour and the stem cells, reducing the threat of relapse in patients whose tumours carry a protein marker called HER2
The study was conducted in two parts where the researchers took biopsies from the tumours of patients before and after treatment.
In the first, 31 patients whose tumours did not have the HER2 marker were given conventional chemotherapy. In the second part, 21 patients whose tumours carried the HER2 marker were given lapatinib and two other common breast cancer drugs.
The researchers tainted the samples to highlight the subset of tumour cells that contained the stem cells, which can be identified by the presence of certain markers on the cell surface.
This enabled them to estimate the percentage of stem cells in the biopsy. In addition, stem cells in the laboratory can grow into colonies of cells that scientists call mammospheres. Because of this, they could also measure those to estimate what proportions of stem cells are present in a sample.
The findings revealed that patients treated with conventional chemotherapy showed a decrease in tumor cells and there was a greater proportion to differentiated tumour cells after treatment. There was a higher percentage of stem cells because the chemotherapy killed the regular tumour cells but left stem cells behind.
Those treated with lapatinib also showed a decrease in the tumour cells but the percentage of breast cancer stem cells did not change or even went down slightly. However, significant tumour shrinkage was greater than patients receiving conventional therapy.
"The tumour shrank dramatically," said Dr. Jenny Chang, associate professor of medicine at BCM and medical director of the BCM Breast Care Cancer Centre.
"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 tumour," he added.
The study appears online in the Journal of the National Cancer Institute.