A presentation at a recent conference again raises concerns about the link between the use of antibiotics and increased risk of colorectal cancer in younger adults.

Results were presented recently at the ESMO World Congress on Gastrointestinal Cancer and heighten concerns about the consequences of the estimated 65% increase in global antibiotic consumption reported between 2000 and 2015. No direct cause and effect were demonstrated, however.

“To our knowledge, this is the first study to link antibiotic use with the growing risk of early-onset colon cancer—a disease which has been increasing at a rate of at least 3% per year over the last two decades. Junk food, sugary drinks, obesity and alcohol are likely to have played a part in that rise, but our data stress the importance of avoiding unnecessary antibiotics, especially in children and young adults,” said medical student Sarah Perrott, from the University of Aberdeen in Scotland. Perrott presented the data.

Researchers used a large Scottish primary care database of up to 2 million people to extract information on nearly 8,000 colorectal cancer patients, matching them with people without bowel cancer. They determined that antibiotic use appeared to be linked to an increased risk of colon cancer across all ages, but the risk was increased by almost 50% in those aged more than 50 years compared with 9% in those aged more than 50 years.

Specifically, the authors report, antibiotic use showed an association with cancers in the first part of the colon (the right side) in younger adult patients; that was especially the case with quinolones and sulfonamides/trimethoprim, they add.

Senior author Leslie Samuel, MSc, of the Aberdeen Royal Infirmary posits that this occurs because the contents of the right side of the colon are more liquid, and that the microbiome could be different from further along the colon.

“We now want to find out if there is a link between antibiotic use and changes in the microbiome which can make the colon more susceptible to cancer especially in younger people,” Samuel suggested. “It’s a complex situation as we know that the microbiome can quickly revert to its previous state even when the bowel has been cleared out for a diagnostic procedure such as an endoscopy. We don t yet know if antibiotics can induce any effects on the microbiome that could directly or indirectly contribute to development of colon cancer.”

In an ESMO press release, Alberto Sobrero, MD, of Ospedale San Martino in Genoa, Italy, pointed out that younger adults aged 20 to 40 years with colon cancer often have a worse prognosis because they are often diagnosed later.

“Physicians are less likely to investigate a patient with abdominal discomfort for colon cancer if they are in their 30s than if they are in their 70s, and younger patients are not eligible for bowel cancer screening. As a result, their cancer is usually diagnosed at a later stage, when it is more difficult to treat,” he said.

“It is too early to say if excessive use of antibiotics could be a causative factor, and we need to understand more about the possible role of the microbiome in bowel cancer before we consider the impact of antibiotics on the intestinal flora,” Dr. Sobrero stated. “However, the new research does remind us that antibiotics should not be given unless they are really needed, and we cannot exclude the possibility that unnecessary use of antibiotics may be exposing people to an increased risk of cancer.”

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