Breast cancer can return 20 years after a woman is first diagnosed, a study has revealed.
Oxford University researchers found the disease can ‘lie dormant’ for years, reappearing long after patients are given the all-clear.
Scientists said in future women might be told to continue taking hormonal drugs for longer than the current five years, in a bid to stop tumours returning.
Scientists analysed data from 88 clinical trials involving 62,923 women, all of whom had the most common form of breast cancer fuelled by the hormone oestrogen.
Every patient received pill treatments such as tamoxifen or aromatase inhibitors which block the effects of oestrogen or shut off the hormone’s supply.
After five years of therapy, their cancers had gone and they stopped taking the drugs.
Women may be told to continue drugs like tamoxifen for longer, say researchers (stock photo)
But monitoring the women’s progress revealed recurrences of the disease up to 15 years later – 20 years after initial diagnosis.
Breast cancer is the most common cancer among British women, with more than 55,000 diagnosed each year.
Survival rates have significantly improved in recent years.
In the past most people with cancer were likely to die within a few years, but medical advances mean patients are more likely to survive for many years – which is why scientists are learning for the first time that tumours can come back so long afterwards.
Lead researcher Dr Hongchao Pan, from Oxford University, said: ‘It is remarkable that breast cancer can remain dormant for so long and then spread many years later, with this risk remaining the same year after year and still strongly related to the size of the original cancer and whether it had spread to the lymph nodes.’
Key findings
Women who started off with large tumours and cancer that had spread to four or more lymph nodes faced the highest risk of recurrence, the study showed.
They had a 40 per cent risk of cancer returning in a different part of the body over a period of 15 years after stopping treatment.
For patients diagnosed with small, low-grade cancers that had not spread the risk was 10 per cent.
Recent research has suggested that extending hormone therapy to 10 years may be more effective at preventing breast cancer recurrence and death.
Doctors have long known that five years of tamoxifen reduces the risk of recurrence by about a third in the five years after stopping treatment.
Aromatase inhibitors, which only work for post-menopausal women, are believed to be even more effective.
However some patients choose to halt hormone treatments early because of side effects such as menopausal symptoms, osteoporosis, joint pain or carpal tunnel syndrome.
The research, which was funded by Cancer Research UK and conducted with experts from the University of Michegan, was published last night in the New England Journal of Medicine.
Reducing risks
Professor Arnie Purushotham, Cancer Research UK’s senior clinical adviser, said: ‘This research shows that stopping hormone treatment at five years leaves women with an ongoing risk of breast cancer coming back in the distant future.
‘It’s important to point out that since this research began, new drugs are being used to treat breast cancer, and these work in a different way to tamoxifen.
‘It’s vital that work continues to better predict which cancers might return.
‘We also need to know what the difference for women might be in taking hormone therapies for 10 years instead of five, the side-effects and how this affects patients’ quality of life.’
Professor Daniel Hayes, of the University of Michigan comprehensive cancer centre, added: ‘We now know that continuing to take anti-oestrogen therapy beyond five years can reduce the risk of recurrence but it’s hard to know whether these benefits will outweigh the possible side effects of continuing treatment.
‘This study shows us what the risk would be if women stop treatment at five years and this gives us a good idea of what the likely benefits of continuing therapy would be for each individual patient and so helps them and their health care providers decide whether to continue treatment.’