Breast cancer cells break away and spread to other parts of the body relatively late on in breast tumour development, shows a new study that could help refine cancer therapy.
The study was published in the journal Genome Biology.
The group's findings suggest there is a longer window than previously thought for cancer to be diagnosed and treated before it spreads. The majority of people who die from cancer lose their lives when it spreads throughout the body, a process called metastasis.
"Although how tumours spread throughout the body is not well understood, we do know that some mutations increase a cell's ability to move about," said first author Jonas Demeulemeester of the Francis Crick Institute in London.
"Cells like this may leave the crowded environment of the primary tumour and enter blood vessels. Swept away by the bloodstream, they may exit the vessels again at distant sites and nest themselves in other tissues, such as the bone marrow. Cells surviving this whole process are known as disseminated tumour cells and can lay undetected and dormant for many years, often resisting therapy, before re-activating and giving rise to a new tumour, a metastasis," he added.
The team of scientists tracked the genetics of particular cancer cells that can go on to form secondary tumours in other parts of the body, such as the bone marrow.
Such cells are known as disseminated tumour cells or DTCs.
The team used the latest single-cell sequencing techniques to read out the full DNA genomes of 63 individual cells isolated from bone marrow samples donated by six breast cancer patients.
The scientists found that they have not only shown that cancer cells spread late, but also that when DTCs are present elsewhere in the body they are genetically very similar to the patient's original tumour.
This knowledge could help clinicians to choose the therapy most likely to destroy the cancer.
Although the project focused on breast cancer, the team believes the results could be applied to other cancers too.
The team developed sensitive methods to interrogate the genome of each sample that allowed them to spot both large and small-scale genetic changes.
They found that when DTCs are present they are genetically very similar to the patient's original tumour.
"This knowledge is crucial to help determine the right therapy for patients. If a treatment is chosen specifically to target a mutation present in all cells of a patient's primary tumour then it is most likely the disseminated tumour cells will also carry this mutation and will also respond," explains Demeulemeester.
Demeulemeester said: "Only a subset of those cells previously believed to be cancer cells have really spread from the patient's primary tumour. A refined indicator means a more accurate prognosis and a more tailored therapy for patients, avoiding over- or under-treatment."
Justine Alford, Cancer Research UK's senior science information officer said, "When cancers spread they are often harder to treat, but this new study could help researchers develop new ways to tackle the disease more effectively.
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