The number of women aged 65 or over living with breast cancer is set to rise to more than 1.2 million by 2040.
New research from King's College London claims today's figure of 340,000 will quadruple in the next 30 years.
At present, 59% of all breast cancer survivors are over the age of 65 but the research, funded by Macmillan Cancer Support, suggests that this figure will increase to 73% by 2040.
The data, published in the British Journal of Cancer , also suggests that by 2040 breast cancer will account for more than half of all cancer cases in women in the UK.
Ciaran Devane, chief executive of Macmillan Cancer Support, said: "The NHS needs to take heed of these figures.
"It is already struggling to provide adequate care for older breast cancer patients.
"We need to change the way we care for older breast cancer patients now - so that we are prepared for such a dramatic increase in numbers."
Dr Rachel Greig, senior policy officer at Breakthrough Breast Cancer , said: "It is startling to think that we could have a million older women living with breast cancer within a generation.
"It shows that we have a rapidly ageing population - but also that we are getting much better at treating women with breast cancer.
"However, increasingly we should think less about the age of patients, and more about their individual need."