With rates of bowel cancer rising around the world among young patients with no risk factors, researchers have begun to question whether antibiotics may be playing a role.

Antibiotics are used to treat bacterial infections. Some are highly specialised and are only effective against certain bacteria.
Others, known as broad-spectrum antibiotics, attack a wide range of bacteria, including ones that are beneficial to us.
Antibiotic therapy has been previously shown to influence bowel cancer development by altering gut microbiome structure and diversity.

A 2017 study published in the medical journal Gut found extended use of antibiotics significantly increased the chance of polyp formation in the bowel, which can be a precursor of bowel cancer.

The findings added weight to evidence that the type and diversity of bacteria in the gut play a key role in the development of cancer, according to the study authors.

A new study, led by Sarah Perrott of the University of Aberdeen in Scotland, has found that the use of antibiotics may also be associated with an increased risk of bowel cancer in younger patients.

In a presentation at the virtual World Congress on Gastrointestinal Cancer, Ms Perrott noted that the incidence of young bowel cancer has been increasing globally, alongside increased antibiotic consumption.

Perrot and her colleagues found that most classes of antibiotics were not significantly linked with colon, rectal, or distal colon cancers; however, quinolones and sulfonamides/trimethoprim were associated with proximal colon cancer in the young-onset group.

“No association was observed with rectal cancer,” Ms Perrott noted, “which we find interesting, in that rectal cancer is a common cancer site in early-onset colorectal cancer compared to later onset.”

Quinolones are considered broad-spectrum antibiotics. This means they work against a wide range of bacteria. However, because they can cause serious side effects, they aren’t recommended for common conditions like sinusitis, bronchitis, and uncomplicated urinary tract infections (UTIs), and should only be considered when treatment with other, less toxic antibiotics, has failed.

Sulfamethoxazole and trimethoprim combination is used to treat infections, such as bronchitis, middle ear infection, urinary tract infection, and traveller’s diarrhea. It is also used for the prevention and treatment of Pneumocystis carinii pneumonia (PCP).

“More epidemiological and translational studies are required to evaluate the true role of antibiotics in the development of colorectal cancer and also to evaluate the long-term effects of antibiotics on gut health,” Ms Perrott said.

Many of the complex surgeries that have become routine around the world are possible today because of antibiotics. Without them, modern medicine would be set back by decades. Surgeries such as appendectomies could become life threatening, as they were prior to the wide availability of antibiotics.

Antibiotics are also used in some patients prior to surgery to ensure they don’t contract any infections from bacteria entering open cuts. Without this precaution, the risk of blood poisoning would become much higher, and many of the more complex surgeries doctors now perform might not be possible.

The message to be taken from the research is not to use antibiotics for a “tickle” in the throat or a common cold.

“With cases of colorectal [bowel] cancer increasing among young, non-obese patients with no risk factors, our study provides further reasons to reduce, where possible, frequent, and unnecessary antibiotic prescribing,” said Ms Perrott.