I was horrified to read this week about the case of 23-year-old Milli Tanner whose bowel cancer was dismissed 13 times by doctors who told her that she was too young to have the disease.

Milli, who first went to her GP at 19, was told that her symptoms were likely due to piles, irritable bowel syndrome (IBS) or period problems. 

Some doctors even suggested that excessive alcohol consumption might be to blame for the issues, which included stomach and lower back pain, as well as blood in her stool.

By the time she was eventually diagnosed, Milli's cancer had reached stage 3 – meaning it had begun to spread to the lymph nodes.

Shockingly, Milli – who had surgery, radiotherapy and chemotherapy – only got a diagnosis because she ordered and paid for a test herself.

What I find most terrifying about Milli's story is that it is not an anomaly. Cancer cases in young people are often missed by doctors. NHS data shows that in more than four in ten cases where a child was diagnosed with cancer, the family was forced to take them to their family doctor at least three times before they were referred for tests.

Often, this is because cancer symptoms can appear differently in young people. But it's also because doctors don't always expect to see the disease in people under the age of 50.

In recent years, there have been several high profile cases of young patients who died due to these delays.

At the same time, deadly bowel cancer cases are on the rise in young people – making cases like Milli's all the more concerning.

I should know – because I was diagnosed with bowel cancer at a young age. And, despite being a GP I didn't recognise the symptoms. It was only by luck that I was diagnosed in time to save my life.

So, here are the bowel cancer symptoms that you must always look out for – and exactly what to say to your GP if you feel they aren't taking you seriously.

I was 39 when I was diagnosed with bowel cancer and, six years on, I still remember the day I found out I had the disease like it was yesterday.

I'd begun to experience pain in my pelvis. However, I'd had similar aches for the previous four years, following my third Caesarean section. I had no other noticeable symptoms – the only reason I brought up the issue with my gynaecologist was because the pain seemed to have gotten worse.

My initial assumption was that the pain was simply due to scar tissue. No one, including myself, ever considered the possibility that it could be cancer.

My gynaecologist believed the symptoms might be due to the fact that my womb had become stuck to my bowel with scar tissue. He suggested I see a bowel surgeon before considering surgery to separate the organs.

It was this decision that ultimately saved my life.

The surgeon suggested a colonoscopy – a medical procedure that involves inserting a camera into the bowel – and that was when they found the cancer.

What followed was multiple life-saving surgeries to remove the disease as well as six months of chemotherapy.

Today, I'm thankful to say I'm currently cancer-free, but many others are not so lucky. Every year, 35,000 people under the age of 50 are diagnosed with cancer in the UK. And many are diagnosed late because doctors don't expect them to have the disease.

Some of this may be due to the way that doctors are trained. In medical school, we were taught the principle of 'Occam's razor', which is essentially a fancy way of saying that the simplest explanation for an issue is the most likely answer.

And since cancer is still primarily a disease that affects the over-50s, it is often not initially considered as a possible cause of new symptoms in young people.

When a 34-year-old presents with a cough, it's more likely to be a viral infection than lung cancer. A 24-year-old with abdominal pain has a greater chance of having irritable bowel syndrome than bowel cancer.

So, in many cases, young people with cancer are forced to return to their doctor multiple times before they are sent for tests that reveal signs of the disease.

This is particularly concerning for those who develop bowel cancer – the only form of the disease that is rising faster in those under the age of 50 than in older adults. Research shows diagnoses in 25 to 49-year-olds have increased by more than 50 per cent since the early 1990s.

Like all cancers, catching it early before it spreads can be the difference between life and death.

The symptoms of bowel cancer include a change in your bowel habit for three weeks or more.

Everybody has a bowel habit, you might do a poo three times a day or you might go three times a week, either way if that is normal for you it is your usual bowel habit.

If that changes, diarrhoea, constipation or even softer poo, going more or less frequently than normal it needs to be assessed.

Bleeding from the rectum, or back passage, which may be on the paper or mixed with the stool or the water in the toilet and may make your poo look red or black as well as pain in the tummy all need to be checked out.

Other symptoms can include a noticeable lump or mass in the abdomen or unintentional weight loss, where you are losing weight without trying.

Unexplained fatigue or shortness of breath can also be signs of bowel cancer. This is because both can be triggered by the loss of small amounts of blood in the stool over a long period of time, perhaps so small you can't see it with the naked eye.

These symptoms are not necessarily due to cancer. Haemorrhoids and anal fissures, which can lead to bleeding from the rectum, are both more common than bowel cancer and fatigue have a multitude of causes.

However, patients need to see a doctor so that the risk of cancer can be ruled out.

If your GP doesn't take your concerns seriously then there are certain phrases you can deploy.

Patients should explicitly state that they are concerned about the risk of cancer. It's possible that the GP may not consider this possibility until it is mentioned.

If a GP refuses to send a patient for further tests, then a patient can simply ask them to explain their reasoning for not doing so.

Patients can also ask to seek a second opinion from a different GP at the same surgery, if they are concerned about the decision their family doctor has made.

Moreover, since September, concerned patients and families can now request an urgent review of their diagnosis under a new NHS guideline named Jess's Rule.

It is named after Jessica Brady, who died of cancer at 27 after being dismissed by her GP surgery 20 times.

The rule states that if a patient's symptoms persist after three appointments with their GP, then their family doctor is obligated to take further action.

This might involve getting the second opinion of a colleague or referring the patient to a specialist. So, if you feel that this applies to you or a family member, then you should contact your GP surgery and request a review under Jess's Rule.

Put simply, you are never too young to have cancer.

That's why advocating for yourself is so vital.