People are twice as likely to live at least 10 years after being diagnosed with cancer than they were at the start of the 1970s, new research shows.
More than 170,000 people in the UK who were diagnosed in the 1970s and 1980s are still alive - an "extraordinary" number, Macmillan Cancer Support said in its report Cancer: Then And Now.
The increase in long-term cancer survivors is due to more sophisticated treatment combined with an ageing population, the charity said, acknowledging there was still a huge variation in survival rates according to cancer type.
However, it warned the consequences were increasing demand on the NHS, with more people living for longer with long-term side-effects.
Macmillan chief executive Lynda Thomas said: "More and more people are being diagnosed with cancer and, in general, having a more sophisticated life with their cancer than perhaps they would have done.
"What we are now seeing is that lot of people are coming in and out of treatment, so all of that does put pressure on the NHS."
Around 625,000 people in the UK are estimated to be facing poor health or disability after treatment for cancer.
Long-term consequences can range from painful lower-leg swelling in women following breast cancer to emotional trauma, and with the numbers of people living with cancer in the UK set to grow from 2.5 million people to four million by 2030, more people will need support.
Mrs Thomas said: "About one in four cancer patients will come out of cancer treatment with really, really debilitating and very serious side-effects - and they can be things like incontinence, or experiencing serious sexual problems, and those are the things we tend not to talk about but they can be the things that really result in people having a very poor life experience after their cancer diagnosis."
The challenge for medical professionals is to "keep up to speed" with the potential side-effects as new treatments emerge, she said.
Some 116,000 cancer patients last year in England did not have the potential long-term side effects from their cancer fully explained to them, she warned.
"It does happen from time to time we will meet patients who've said 'I had no idea this was going to happen', I hope that's happening less and less now, particularly as professionals become better at explaining the consequences of treatment.
"But it's important people recognise that issues such as fertility might be affected, or you might have heart problems later on in life.
"You never want to somebody to say 'I wish I'd known that before because I would have done something different'."
Macmillan also estimates that there could be around 42,500 people who were diagnosed with cancer in the 1970s and 1980s who may still be dealing with long-term consequences.
After suffering cancer as a child, Greig Trout developed scoliosis, deep vein thrombosis and eczema. He struggles to put on muscle or fat in his upper body, has physiotherapy for his back and takes blood thinning pills every day.
Doctors believe his second bout of cancer, diagnosed when he was 30, could be a result of the radiation therapy he received more than two decades prior.
The 37-year-old from Thames Ditton, south-west London, said: "The life-saving treatment I had as a child has come back to bite me in the future, but I'm still here.
"I think GPs... it would be good for them, especially now with people who are struggling with side-effects of treatment back in the 80s, just to know and be more aware of what those side-effects are.
"Developments of cancer treatment are just getting better and better so I hope that more people don't have to go through what I've been through as a child. I'm just trying to enjoy every day as it comes and just grateful to be here."