It's a story that's been told over and over by young bowel cancer patients. 

A collection of relatively minor gut symptoms are mistaken, often by multiple doctors, for benign irritable bowel syndrome (IBS) – a collection of digestive problems that affect about a fifth of adults.

The late Dame Deborah James was one of those patients. Multiple visits to the GP resulted in the conclusion she 'probably had IBS or, at worst, colitis'. 

It wasn't until almost a year later that a private internal scan revealed a large tumour in her bowel, which went on to spread to her lungs. 

IBS usually causes symptoms like diarrhoea, constipation and abdominal pain, often in response to eating certain foods, stress or other factors. 

While the signs of IBS and bowel cancer can be similar, doctors say there are key differences that too few know about.

Dr Asiya Maula, a GP at The Health Suite, says one symptom that's often a sign of something more sinister is regular 'incomplete' bowel movements. 

By this, she means: 'The sensation of needing to open your bowels even after you have just been to the toilet.

'Medically, we call this incomplete bowel emptying. A growth in the bowel or rectum can sometimes cause a feeling of pressure or irritation, or partially obstruct the passage of stool, which can leave someone feeling as though they still need to go even after they have emptied their bowels.'

However, Dr Maula adds that bowel cancer isn't the only reason this happens – and there may be another, less serious explanation. 

But if the feeling is persistent and a change in what is normal for you, it is worth discussing with a GP, she adds. 

Another warning sign can be if the gut problems come alongside exhaustion and even breathlessness. 

This can be a sign of anaemia – whereby the blood can't carry as much oxygen as it should, causing fatigue and low energy. The condition can develop as a result of blood loss, potentially triggered by a tumour. 

Blood in the stool is a commonly known sign of bowel cancer but Dr Maula warns younger people all too often assume it's simply a result of an existing haemorrhoid.

'Do not simply write it off because you are in your twenties, thirties or forties,' she says. 

'There is a tendency among younger people to wait and see if symptoms disappear, particularly when they are busy or think there is an obvious explanation. 

'Your GP would much rather investigate a symptom that turns out to be harmless than have someone delay seeking help because they thought they were too young to have bowel cancer.'

The warnings come as bowel cancer cases in under-50-year-olds have risen by more than 50 per cent over the last two decades. 

Dr Maula's advice follows that of Bristol-based GP Dr Jack Ogden last year, who urged patients to get checked if they notice lesser-known symptoms.

These included 'pencil thin' stools, which he said can be an indicator that a tumour is obstructing the colon causing it to squeeze stool into a thinner shape.

Meanwhile, losing weight without changing diet or exercising more is another telltale sign.

Worryingly, he said it doesn't have to be sudden – it can also be subtle or gradual.

Often this weight loss can be caused by increased metabolic demand, loss of appetite and tumours preventing the absorption of nutrients. 

Last week, an alarming US study highlighted a particular surge in teenage diagnoses, with those under 21 being struck down with especially aggressive forms of the disease. 

In a study of patients aged 21 and under at 34 US hospitals, the researchers found that 45 per cent died and 37 per cent saw their cancer return within a year. 

Among these patients, back or abdominal pain was reported by a third as an early symptom, while just under half (45 per cent) experienced a change in bowel habits.     

Experts have previously blamed the rise in diagnoses on poor diets, sedentary lifestyles and increasing obesity rates.

However Dr Maula warns against assuming one particular food, habit or lifestyle factor is responsible for the rise.

'It is important not to jump to conclusions about why rates are increasing while researchers are still investigating the causes.'

Cancer Research UK recently launched a major new study investigating why bowel cancer is increasingly affecting younger people, with researchers aiming to recruit 250,000 UK adults to help identify potential causes.

Called PROSPECT-UK, the trial is set to investigate whether factors including diet, lifestyle, gut health and environmental exposures could be playing a role.

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