Almost 80,000 people in the UK were diagnosed before the age of 45 and are still living with one of the top four most common cancers, according to research.
The data shows that almost 550 men living with prostate cancer in the UK and 2,000 people with lung cancer were diagnosed before the age of 45 - suggesting that cancer is not just an old-age disease.
The findings come from a joint research programme between Macmillan Cancer Support and Public Health England's National Cancer Intelligence Network (NCIN) being launched today at the Cancer Outcomes Conference in Belfast.
Around 10,000 people are living with colorectal cancer who were diagnosed before 45, with more than 600 of these diagnosed before the age of 25.
The data also highlights that around 66,500 women are living with breast cancer who were diagnosed before the age of 45.
Whilst awareness may be higher of people living with breast cancer at all ages, the charity is particularly shocked by the numbers diagnosed and still living with prostate, colorectal and lung cancer from this young age, as these cancers are traditionally associated with old age.
This is despite the fact that each year the number of new people under 45 diagnosed with these four cancers represents only 10% of the total number of new cancer cases.
The research reveals that around 30,000 (over a third) of those diagnosed under the age of 45, were diagnosed more than 10 years ago and are still living today. The charity is warning that many of these people may not return to full health for decades to come, or for the rest of their lives, after the serious side effects of the disease and treatments.
Additional Macmillan research shows that people living with cancer aged 25-49 often have other health problems to cope with, with more than one in three (39%) managing at least one other condition.
Luke Bennett, 33, from Essex was diagnosed with bowel cancer in 2007.
He said: "I was only 27 when I was told I had cancer after suffering six months of pain which I put down to IBS or bad kebabs. I did the bloke thing and ignored it until my girlfriend, now wife, made me go to the GP who instantly referred me.
"Treatment was tough so the last day of chemotherapy was the best ever, but seven years on I'm still living with some side effects: my fingers feel weird, my body does ache and I get pain in my kidneys which they're investigating."
Juliet Bouverie, director of services and influencing at Macmillan Cancer Support, said that there was reason to celebrate that a cancer diagnosis did not necessarily mean the death sentence, as it once did.
She added: "But the sad reality is that many people of this age may be struggling to hold down a job, support a family, and deal with the emotional impact of cancer whilst also going through treatment. What's more, our research shows that many could be doing so for years as they live with and struggle to manage the debilitating side effects of cancer treatment, such as fatigue, pain, problems with mobility or depression with little, if any, support.
"Sadly the NHS isn't set up to support the individual, complex and long term needs people may face when treatment finishes. People are usually left to cope alone apart from the occasional follow-up appointment to check that the tumour hasn't come back.
"Macmillan is urgently calling on the new Government to commit to ensuring that every person with cancer receives an assessment of their emotional, physical, spiritual and social needs and a personalised 'Recovery Package' of care based on their needs when treatment ends."
Ms Bouverie suggested that the package could include guidance on keeping active as part of a healthy lifestyle and information on how to manage the physical consequences of treatment, and details on how to access.
"Only in this way will the NHS be able to support a rapidly growing number of cancer survivors with the long term impact of cancer and give them a decent quality of life in the years after their treatment ends," she concluded.