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A new study published in the New England Journal of Medicine has found that the risk of breast cancer recurring persists undiminished for at least 20 years after diagnosis, suggesting that hormonal treatments should continue for even longer to reduce the risk of late recurrence.

Mammogram

The Early Breast Cancer Trialists’ Collaborative Group, an international team of investigators based in the Nuffield Department of Population Health, pooled data from over 60,000 women in 88 clinical trials who had been diagnosed with estrogen receptor positive breast cancer and prescribed anti-estrogen therapy, such as tamoxifen or an aromatase inhibitor, for 5 years. Women who had no recurrence in the first 5 years, then stopped treatment and their progress was followed for up to 15 further years.

Over 11,000 of these women had a recurrence of cancer elsewhere, such as the bone, liver, or lung, with the risk of recurrence during each subsequent year (from years 5-15) remaining about constant. The risk of recurrence was strongly related to the presence and number of involved axillary lymph nodes at diagnosis, as well as the size and pathologic grade of the cancer. The highest risk of recurrence was among women with 4 or more involved axillary nodes, who had a 40% risk of a distant cancer recurrence 20 years after first diagnosis. Even women with the lowest risk, i.e. those with small, low grade cancers and no spread to the nodes, had a 10% risk of distant spread by year 20.

Professor Daniel F Hayes, senior author of the study from the University of Michigan Comprehensive Cancer Center, commented “We now know that continuing taking anti-estrogen 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 5 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.”

Professor Richard Gray, a lead author from the Nuffield Department of Population Health said “To assess 20-year risks, we studied women who received their breast cancer diagnosis many years ago, and 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. This study shows why all women with estrogen receptor positive breast cancer should at least consider taking anti-estrogen therapy beyond five years and may also help motivate women who are experiencing side-effects to persist with treatment. This improved understanding of the factors that raise the risk of a late recurrence will help women and their doctors make individual decisions on how long to continue hormonal treatment."