The risk of a certain type of breast cancer coming back in other parts of the body stays constant for at least 20 years after treatment, according to a large study.
The research, carried out by The Early Breast Cancer Trialists’ Collaborative Group, collected data from more than 60,000 women who had been diagnosed with hormone sensitive breast cancer (usually called oestrogen receptor positive or ER+ breast cancer) between 1976 and 2011.
All of the patients were given a type of anti-oestrogen therapy, such as tamoxifen or an aromatase inhibitor, for five years as part of their treatment. At the five year mark the women had no signs that their breast cancer had come back and treatment ended.
The current treatment for women with ER+ breast cancer is for them to take anti-oestrogen therapy for five years, but in some cases they take it for longer.
The figures, published in the New England Journal of Medicine, show that out of the women included in the study, 11,000 had their cancer come back in another part of the body such as the bone, liver and lung in the 15 years after stopping treatment. They also showed that the risk of cancer coming back remained the same year on year from when they stopped taking the anti-oestrogen drugs to 15 years later.
Dr Hongchao Pan, a lead researcher on the study from the University of Oxford, said it was “remarkable” that breast cancer can remain dormant for so long and then spread many years later. He said that the risk remained the same each year and was still “strongly related to the size of the original cancer and whether it had spread to any lymph nodes.”
Women who were diagnosed with ER+ breast cancer that had spread to four or more lymph nodes had the highest risk of their cancer coming back 20 years after diagnosis. Those who had a small, early stage tumours had the lowest chance of their cancer returning after treatment.
Professor Richard Gray, also a lead researcher, acknowledged that in order to assess the risk over 20 years the team had to study women who were diagnosed with breast cancer many years ago, as far back as 1976.
“We know that treatments have improved since then so women who were diagnosed more recently may be reassured that recurrence rates will be somewhat lower for them.”
Gray said that the study shows it’s important for women with ER+ breast cancer to continue with their anti-oestrogen therapy for longer than the recommended five years. He hopes that these results will motivate women who are experiencing side-effects while on this treatment to persevere with it.
The research confirms that taking these drugs for five years does not remove the risk of breast cancer returning. This risk remains the same even after five years of treatment.
Professor Arnie Purushotham, Cancer Research UK’s senior clinical adviser, also pointed out that “since this research began, new drugs are being used to treat breast cancer that are better at preventing recurrence than those given to most women in this study.”
Purushotham said it is “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 5, the side-effects and how this affects patients' quality of life,” he added.