Researchers have revealed a protein marker called Lgr6 on the surface of certain progenitor cells in breast tissue that can give rise to tumours.
The study offers insights into how some kinds of breast cancers originate and may lead to further research into possible treatments.
Fabio Pucci in Axel Behrens' group at the Francis Crick Institute worked with Leander Blaas at the Karolinska Institutet in Sweden to carry out much of the work.
Fabio explains: "Progenitor cells are cells that normally divide and produce the different parts of a tissue. They are a step further developed than stem cells, or the immature cells that have not yet developed into the specialised cells that make up our organs and tissues. Mutations in progenitor cells are particularly dangerous because they can take advantage of the cells' natural ability to divide and instead create a tumour."
The progenitor cell populations in the breast, or mammary gland, and the types of cell that give rise to breast cancer are not well understood. Lrg6 is a protein that marks stem cells of taste buds, lung and skin, as well as rare mammary gland cells. However it wasn't known whether Lrg6 marks mammary progenitor cells as well.
The researchers used genetic techniques to fluorescently label Lgr6 cells in healthy mice and mice genetically engineered to develop breast cancer. (The fluorescent labels allowed them to see the Lgr6 cells under the microscope).
This revealed that Lgr6 cells are very active in the normal expansion of the mammary gland during puberty and pregnancy, and can initiate and sustain tumours when mutated.
The scientists generated mice where the Lgr6 cells could be specifically targeted with a toxin. This showed that that killing cancerous Lgr6 cells in mice reduces the tumour growth.
Dr Behrens says: "Although this work was carried out mainly in mice, we also found that around half of human breast cancers contain Lgr6 cells, and that these tumours tend to be more aggressive. In the future it might be possible to target Lgr6 cells in some way to reduce the growth of the tumour, but we don't know yet how this could work in humans.
"We also know that other organs, such as the skin, contain Lgr6 cells and further research could find out whether Lgr6 cells can initiate and sustain tumours in these other organs."
The paper, Lgr6 labels a rare population of mammary gland progenitor cells that are able to originate luminal mammary tumours, is published in Nature Cell Biology.