Antibiotic use may be contributing to the increase in early-onset colorectal cancer (CRC) observed in recent years, a new study suggests.1

The study was presented at the European Society for Medical Oncology (ESMO) World Congress on Gastrointestinal Cancer 2021 by Sarah Perrott, a medical student at the University of Aberdeen in Scotland.

Ms Perrott noted that rates of early-onset CRC (defined as CRC in adults younger than 50 years of age) have been increasing since the late 1980s. At the same time, antibiotic use has been on the rise. Furthermore, antibiotics have been shown to alter the gut microbiome and influence CRC genesis in older adults.

“However, later-onset colorectal cancer is often considered a completely different disease to early-onset colorectal cancer in terms of the epidemiology, pathology, and biology,” Ms Perrott said. “And no study before has investigated antibiotic usage in early-onset colorectal cancer.”

Ms Perrott and colleagues conducted a nested case control study to determine if there is a link between antibiotic use and early-onset CRC. The researchers also evaluated antibiotic use in patients with later-onset CRC (at age 50 and older) for comparison.

The researchers analyzed primary care data from patients in Scotland. Patients diagnosed with CRC between 1999 and 2011 were matched with up to 5 control patients.

There were 7903 CRC patients and 30,418 control patients included. Of the CRC patients, 5281 had colon cancer and 2622 had rectal cancer.

The researchers found that antibiotic use was associated with an increased risk of early-onset colon cancer (adjusted odds ratio [aOR], 1.49; 95% CI, 1.07-2.07; P =.018) and later-onset colon cancer (aOR, 1.09; 95% CI, 1.01-1.18; P =.029).

However, antibiotic use was not associated with an increased risk of early-onset rectal cancer (aOR, 1.17; 95% CI, 0.75-1.84; P =.493) or later-onset rectal cancer (aOR, 1.07; 95% CI, 0.96-1.19; P =.238).

Antibiotic use was associated with an increased risk of proximal colon cancer in younger patients (aOR, 3.78; 95% CI, 1.60-8.92; P =.002) but not in older patients (aOR, 0.92; 95% CI, 0.74-1.13; P =.315). Ms Perrott noted, however, that the sample size in this subgroup was small, so further investigation is needed.

“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 2 decades,” Ms Perrott said in a press release.2

“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,” she added.


  1. Perrott S, McDowell R, Murchie P, Cardwell C, Samuel L. Global rise in early-onset colorectal cancer: an association with antibiotic consumption? Presented at: ESMO World Congress on Gastrointestinal Cancer; June 30-July 3, 2021. Abstract SO-25.
  2. Bowel cancer data reinforce need to reduce unnecessary antibiotic use. News Release, ESMO. July 2, 2021.

This article originally appeared on Cancer Therapy Advisor