Ms Siegel told Cancer Therapy Advisor that both the age-adjusted incidence rates and numbers of cases are increasing in younger adults. She explained that obesity, lack of activity, and a high consumption of red meat are all risk factors for colorectal cancers.

“It is not surprising that the timing of the obesity epidemic parallels the rise in CRC [colorectal cancer] because many behaviors thought to drive weight gain, such as unhealthy dietary patterns and sedentary lifestyles, independently increase CRC risk,” Siegel and her colleagues wrote.

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The authors point out that unhealthful dietary elements, which include high-glycemic carbohydrates, trigger a cascade of detrimental health effects.2 Western-style, high-fat, low-fiber diets reportedly begin the inflammatory process and proliferation in the colonic mucosa.3

Dr Venook explained that we still do not know how many years of bad diet it takes to put subjects at risk for CRC. In a study of Japanese migrants to the United States, a one-generation jump in CRC risk was attributed to a diet change.4

Dr Venook also noted that the rapidly evolving field of microbiome may explain whether changes in the flora of the gut may explain some of these observations. He pointed out that Fusobacterium in the gut is associated with an increased risk for CRC. “Is there an increased incidence of this bacterium in young adults?” he asked.

Although early screening is not recommended and early screening at age 45 years would add around 20 million people to the screening-eligible population, the authors indicate that screening initiation before the age of 50 years should be considered.

“The situation merits a detailed analysis,” Dr Venook noted.

“In the absence of these [early screening] recommendations we can do something now,” Ms Siegel said. “It is important to raise the awareness of CRC among young adults and primary care physicians who see these patients,” she said.

RELATED: Wider Use of Genetic Testing Could Lower Colorectal Cancer Incidence

“Importantly, don’t ignore symptoms of CRC,” Dr Venook said. Ms Siegel concurred: “symptoms consistent with CRC, such as abdominal cramping and blood in the stool, should be attended to immediately and make a difference, as 5-year survival of 90% has been reported for early diagnosis of CRC.”


  1. Siegel RL, Fedewa SA, Anderson WF, et al. Colorectal cancer incidence patterns in the United States, 1974-2013.  J Natl Cancer Inst. 2017 February 28. doi: 10.1093/jnci/djw322 [Epub ahead of print]
  2. Ludwig DS. Lifespan weighed down by diet. JAMA. 2016;315(21):2269-70.
  3. O’Keefe SJ, Li JV, Lahti L, et al. Fat, fibre and cancer risk in African Americans and rural Africans. Nat Comm. 2015;6:6342.
  4. Marchand LL. Combined influence of genetic and dietary factors on colorectal cancer incidence in Japanese Americans. J Natl Cancer Inst Monogr. 1999;(26):101-105.