Women with tumours on four or more lymph nodes face a 40 per cent risk of recurrence twenty years after their initial diagnosis
Scientists analysed 88 clinical trials involving 62,923 patients who had the most common form of breast cancer fuelled by the hormone oestrogen.
After five years of therapy, the cancer had gone but data found recurrences up to 15 years later – 20 years after initial diagnosis.
Research suggests ten years of hormone therapy may be more effective at preventing recurrence and death. However some patients choose to halt hormone treatments early because of side effects such as menopausal symptoms, osteoporosis, joint pain or carpal tunnel syndrome.
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.”