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Last year, speakers at the annual American Society of Clinical Oncology meeting – the most eminent cancer conference in the world – came with a dire warning.
Rates of colorectal cancer were rapidly increasing in the under 40s, they said, so much so that cases are expected to double in this age group by 2030, with the disease set to become the number one source of cancer deaths in 20-to 49-year-olds by the end of the decade.
“Studies are showing this increase in early onset colorectal cancer,” says Dr Dimitra Lamprinaki, a researcher at the Quadram Institute in Norwich. “The problem is that some of these cases are asymptomatic but also younger people are potentially ignoring signs of cancer which could progress and then be hard to remove.”
This is part of a general trend. Global cancer cases in the under 50s are rising rapidly, increasing by 79 percent between 1990 and 2019 according to recent research. But while lifestyle factors, such as highly processed diets and heavy alcohol use in the millennial generation, are likely to blame, scientists have discovered an important new connection – microbes which are fuelled by these poor habits and subsequently drive more aggressive and treatment resistant cancers.
Here are some of the main factors which may be driving the increased rates of cancer cases in the young.
Vaping and poor oral hygiene
London-based private clinic Pure Periodontics have witnessed a startling rise in gum disease in younger patients. They attribute this to diets loaded in sugar and acids along with the rise of vaping in the under 40s, a habit which inhibits blood flow to the gums, increasing susceptibility to infections and making healing more difficult.
This all promotes the growth of a particular strain of bacteria called Fusobacterium nucleatum (F. nucleatum) which has been associated with a whole range of cancers including breast, colorectal, and head and neck cancers.
“It’s a very sticky bug which sticks onto the surface of the teeth and gums, and allows other bad bacteria to come in,” says Dr Tim O’Brien, a medical oncologist and researcher at Queen’s University Belfast.
With poorer oral hygiene, these bacteria can proliferate, enter the bloodstream, and access different organs. When these microbes enter early-stage tumours, they can actively interfere with chemotherapy and radiotherapy, enabling the cancer to grow and spread.
“Fusobacterium can contribute to chemotherapy but also radiation resistance,” says O’Brien. “It thrives within the tumour environment so it’s in its interest for the tumour to survive. So it interferes with the process by which chemotherapy causes cancer cells to self-destruct and it can also kick out immune cells which are trying to destroy the tumour.”
High intake of processed meat
According to the journal Nature, one of the sharpest increases in cancer rates in the under 50s has been for stomach cancer.
One of the most well-known risk factors for stomach cancer is the bacteria Helicobacter pylori (H. pylori) which is thought to be responsible for around 40 percent of cases in the UK. H. pylori lives in the mucous layers which line the stomach and contributes to conditions such as atrophic gastritis, the chronic inflammation and thinning of the stomach lining, which can then progress to cancer.
Research has shown that a diet high in processed meats such as sausages, bacon and hamburgers can increase the prevalence of H.pylori in the stomach.
Professor Andrew Beggs, Consultant Colorectal Surgeon at the University of Birmingham, describes the connection between such microbes and lifestyle factors as ‘vital pieces of a puzzle.’
“You have these bacteria and an unhealthy lifestyle with excess red meat, alcohol, and smoking, and some people may also have a genetic predisposition element which increases their risk,” he says. “When you add all those factors up, it leads to a big increase in the risk of cancer.”
Oral sex
It’s not only bacteria which can drive cases of cancer, viruses have also been linked with different forms of the disease. Specialists around the UK have described rising rates of mouth cancer particularly in 40- to 49-year-olds, with half of these cases linked to a strain of the sexually transmitted human papillomavirus (HPV), known as HPV-16 which can be passed on through oral sex.
One possibility could be greater numbers of casual sexual partners, with a study in the journal Cancer finding that kissing and particularly deep kissing, is also linked to heightened risk, with individuals who had 10 or more deep kissing partners twice as likely to develop an HPV-related cancer.
Ultra-processed foods
The F. nucleatum bacteria not only makes cancers more resistant to treatment, but it can also actively drive the disease, especially in the bowel. A new study in Nature published last week, found that mice given a particular subspecies of this bacteria developed pre-cancerous intestinal growths and accelerated tumour formation compared to normal mice.
Researchers who have studied this bacteria as well as certain species of E.coli which have also been associated with colorectal cancer, believe that a diet high in ultra-processed foods can alter the composition of the gut microbiome in a way which enables these species to flourish, increasing the risk of cancer progression via a number of mechanisms.
“Some bacteria enable gut cells to acquire stem cell-like properties which increases the chance of cancer formation at the cellular level,” says Dr Meera Patel, a researcher in the Colorectal & Peritoneal Oncology Lab at the University of Manchester.
“There’s also a theory that certain bacteria can impair the gut vascular barrier which stops the spread of bacteria from your colon to your wider circulation, and if you have an impaired gut vascular barrier, then tumour cells can move out of the colon and metastasise to other organs.”
Excessive alcohol
However, there are other cases of cancer in the young where microbial involvement has not yet been identified.
As an example, testicular cancer is the most common solid tumour cancer which is diagnosed in young men, and according to the NHS, the number of cases identified each year in the UK have doubled since the 1970s for reasons which cancer specialists are still trying to understand.
Family history is one of the biggest risk factors for this type of cancer, but some population studies have also identified a link between excessive drinking and a form of the disease called testicular germ cell carcinoma.
Young men who consumed 14 or more alcoholic beverages per week have been found to be at greater risk, along with a diet high in fat, red meat and dairy products as well as low in fruits and vegetables.
New treatments
However the emerging connection between microbes and different forms of early-onset cancers in the young, could lead to new targeted treatments such as phage therapy which involves administering the patient with specially engineered viruses which are programmed to feed on a particular species of problematic bacteria, or targeted vaccines.
“You could vaccinate mice before infecting them with F. nucleatum and see if it makes a difference in terms of their outcome for polyps and cancers,” says Beggs. “If that’s the case, there will be a strong argument to have a phase one trial in humans to see if it will reduce incidences of colorectal cancer.”
O’Brien predicts that in the coming years, the particular microbial composition of a tumour could be used to determine treatment decisions.
“We don’t currently utilise that information, but in the future, I think we’ll be able to get that and use it to decide whether this is a particularly aggressive tumour, and whether the patient needs a higher dose of chemotherapy,” he says.
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