While mortality remained stable in white individuals ages 20 to 29 from 1988-2014, it increased from 1995-2014 by 1.6 percent per year in those ages 30 to 39 years, and from 2005-2014 by 1.9 percent per year for those ages 40 to 49 years and by 0.9 percent per year for those ages 50 to 54 years.
Overall, mortality rates from colorectal cancer in adults age 20 to 54 declined from 6.3 per 100,000 in 1970 to 3.9 in 2004.
Colorectal cancer rates have been increasing in recent years for Americans below the age of 55, and scientists are unsure why.
"Although the risk of colorectal cancer remains low for young and middle-aged adults, rising mortality strongly suggests that the increase in incidence is not only earlier detection of prevalent cancer, but a true and perplexing escalation in disease occurrence".
Researchers who analyzed frequency, phenotype and familial cancer risk of 82 subjects with colorectal cancer under 55 years of age found that "diagnosis of colorectal cancer under 55 years of age is associated with a high frequency of hereditary or familial cases". The increase thus far is confined to white men and women and is most rapid for metastatic disease.
In white individuals, death rates increased from 3.6 per 100,000 in 2004 to 4.1 in 2014.
This surge in colorectal cancer deaths was particularly surprising since, for decades, screening has been recommended for those 50 years old and up. They focused on people aged 20 to 54 from 1970 through 2014, and specifically on 242,000 colon cancer deaths in that age group.
Mortality rates declined among black individuals by 0.4% (95% CI, -0.6 to -0.3) annually to 1.1% (95% CI, -1.5 to -0.7) annually, from 8.1 per 100,000 in 1970 to 6.1 per 100,000 in 2014.More news: The Gifted will treat the X-Men like 'mythology'
Increased mortality was particularly unexpected among those aged 50 to 54 years, for whom screening has been recommended since the 1970s.
Obesity and the sedentary lifestyle common among many Americans are likely contributing to rising cases and deaths from colorectal cancer, but it's "unclear the extent to which these factors are contributing because of the racial disparity", Siegel said. For the other ethnic groups, the mortality rate has decreased from 1970 to 2006 and then stabilized.
Limitations of the study included its ecologic nature and inaccuracies in about 5% of all death certificates listing colorectal cancer as the underlying cause of death.
Symptoms of colorectal cancer include pain in the abdomen, bloody stool, constipation, weight loss, and change in bowel patterns.
Experts are divided as to whether the findings should prompt a change in screening guidelines. Those at average risk for colorectal cancer should schedule a colonoscopy at age 50 years.
The latest survey on the five-year survival rate, which shows how likely it is that patients diagnosed with cancer will be alive at the end of that period, excludes those who died of other causes.
For more on colon cancer, visit the American Cancer Society.