The Association Between Antibiotic Use and Early-Onset Colon and Rectal Cancer

A study presented by Dr. Sarah Perrot at the 2021 ESMO World Congress on Gastrointestinal Cancer reported findings suggesting that antibiotic use across all patient age groups, particularly in people younger than 50, may be associated with colon and rectal (large bowel) cancer. Although these results do not demonstrate direct cause and effect, they raise new concerns about the estimated 65% increase in global antibiotic consumption reported between 2000 and 2015 and its possible impact.

The First Study of Its Kind

Dr. Perrot says: "To our knowledge, this is the first study to link antibiotic use to an increased risk of early-onset colon cancer. Over the past 20 years, colorectal cancers beginning at a young age have increased by at least 3% each year. Increased consumption of junk food, sugary drinks and alcohol, along with obesity, are probably the main reasons for rising colorectal cancer incidence among young people, but our data emphasize the importance of avoiding unnecessary antibiotics, especially in children and young adults."

Study Details and Results

Using a large Scottish primary care database, the study included approximately 8 thousand people with colorectal cancer, matched to healthy controls.

The researchers found that antibiotic use was associated with an increased risk of colon cancer at all ages, but the risk in patients younger than 50 increased by almost 50% compared with those older than 50. In the younger age group, antibiotic use was associated with cancers in the first part of the colon (the right side). Quinolones and sulfonamides/trimethoprim, used to treat a wide range of infections, were associated with these right-sided cancers.

Study coauthor Leslie Samuel explained that the contents of the right side of the colon are more liquid, and that the natural bacteria living there, called the microbiome, may differ along the colon.

Samuel said: "We now want to investigate antibiotic use and changes in the microbiome to see whether they may be linked in a way that makes the large bowel more susceptible to cancer, especially in young people. Colonoscopy is an example of a diagnostic procedure requiring bowel cleansing, yet we know the microbiome can quickly return to its previous state even after this cleansing. This makes the situation complex. We do not yet know whether antibiotics can have any effect on the microbiome that could contribute directly or indirectly to the development of colon cancer” he said.

Comment

Approximately 2 million people worldwide are diagnosed with colon and rectal cancer each year (see Global Cancer Statistics). Young people diagnosed with colon cancer between the ages of 20 and 40 generally have a less favorable disease course than older patients because they are usually diagnosed at more advanced stages.

Doctors are less likely to investigate colon cancer in a patient in their 30s with abdominal discomfort than in someone in their 70s. As a result, these patients' cancers are often diagnosed at a later stage, when they are more difficult to treat.

Doctors now need to consider colorectal cancer as a possible diagnosis in young patients with abdominal symptoms. The rising incidence of colorectal cancers in this age group supports further research into their multiple possible causes.

It is still too early to say whether antibiotic overuse is a causal factor in young-onset colorectal cancers, and we need to understand more about the possible role of the microbiome in colorectal cancer before considering antibiotics' effects on intestinal flora. Nevertheless, this new research reminds us that antibiotics should not be given unless they are truly needed, and we cannot rule out the possibility that unnecessary antibiotic use may expose people to an increased risk of cancer.