They say the number of elderly people who have been diagnosed with the disease will more than treble by 2040, with over one in four being affected.
In 2010, 1.3 million over 65s had cancer. The figure is predicted to reach 4.1m within 30 years.
Macmillan Cancer Support said it was a ticking time bomb for society.
Age is the biggest risk factor for cancer and greater life expectancy is expected to push up rates.
A study by King’s College London in the British Journal of Cancer tried to work out how common cancer would be in the future.
Across all age groups it predicted the number of cancer survivors would increase by one million every decade between 2010 and 2040 with largest increase in the over 65s.
One of the researchers, Prof Henrik Møller, said: "The research shows that large increases can be expected in the oldest age groups in the coming decades and with this an increased demand upon health services."
The study’s authors concluded: "It is projected that in 2040 almost one quarter of all people in the United Kingdom aged at least 65 years will be cancer survivors.
"This result, in particular, highlights the potential for significant increases in the burden of cancer on health service and community care resources."
However, better treatments or new screening programmes could alter the estimates.