Breast cancer drugs may force some cancer cells into sleeper mode, allowing them to potentially come back to life years after initial treatment.
These are the early-stage findings from researchers at Imperial College London, who studied human breast cancer cells in the laboratory.
For a long time researchers have debated whether hormone therapies - which are a very effective treatment - work by killing breast cancer cells or whether the drugs flip them into a dormant sleeper state.
This is an important question as hormone treatments are used on the majority of breast cancers.
In the study, published in the journal Nature Communications, researchers studied around 50,000 human breast cancer single cells in the lab, and found that treating them with hormone treatment exposed a small proportion of them as being in a dormant state.
The sleeper cells may also provide clues as to why some breast cancer cells become resistant to treatment, causing a patient's drugs to stop working, and their cancer to return.
Hormone therapies are used to treat a type of breast cancer called oestrogen-receptor positive ( ER+ ). These make up over 70% of all breast cancers, and are fuelled by the hormone oestrogen.
These cancers are usually treated with surgery to remove the tumour, followed by a course of targeted hormone therapy - usually either aromatase inhibitors or Tamoxifen, which target oestrogen receptors.
However, around 30% of breast cancer patients taking hormone therapies see their cancer eventually return - sometimes as long as 20 years after treatment.
This returning cancer is usually metastatic, meaning it has spread around the body, and the tumours are often now resistant to medication.
These sleeper cells seem to be an intermediate stage to the cells becoming resistant to the cancer drugs. The findings also suggest the drugs actually trigger the cancer cells to enter this sleeper state.
The research also revealed cells in this dormant sleeper state were more likely to spread around the body.
They could then awaken once in other organs of the body, and cause secondary cancers.
However, researchers still don't know how these cells switch themselves into sleep mode, and what would cause them to wake up.
The hormone therapies remain one of the most effective treatments against breast cancer, and that further patient research will explore whether taking hormone therapies for longer after initial cancer treatment could prevent cancer cells from waking from their sleeping state. ( Xagena )
Source: Imperial College London, 2019