There is a significant increase in the incidence of colorectal cancer in the age group below 55 years. In older individuals, diagnoses have been steadily declining for years. Screening recommendations should be followed more closely overall and screening before age 50 should not be forgotten.
Cases of colorectal cancer have been declining for decades in the U.S., where the new study comes from. This reduction is attributed partly to changes in risk factors and partly to screening – the latter is probably responsible for a sharp drop of 3% annually in recent years. Screening can be used to identify not only full-blown carcinomas but also treatable precancerous lesions, thereby reducing rates of carcinoma diagnosis in the long term.
In contrast, it is unclear exactly how the underlying risk changed across age groups. Some reports do not see an improvement in risk factors; rather, they suggest an increase in risk among people younger than 50. The registry study by Siegel et al. is now stepping into the same breach.
Would this mean that more people under the age of 50 would need to be screened? Is there a need for increased awareness and sensitization among physicians, as well as the general population, to avoid missing screening in younger individuals at increased risk and thus identify more precancerous lesions and early rather than advanced carcinomas?
Two different trends
The aim of the retrospective cohort study was to provide clarity on current trends. To do this, they collected data from the high-quality U.S. SEER registry. All diagnoses of invasive colorectal cancer in patients 20 years of age and older between 1974 and 2013 were compiled. To avoid compromising statistical power, we did not stratify the data by sex but did stratify by age at diagnosis, age at birth, and tumor location. In total, approximately half a million diagnosed cases were found during the study period.
Trend 1 – Decrease in the elderly: What is certain is that in the older population aged 55 years and older, incidence rates of colon cancer also declined in this study, and have been declining since the mid-1980s. The same has been true for rectal cancer since the mid-1970s. One can only speculate about the reasons for this decline well before the introduction of nationwide screening efforts. Is it actually due in part to the shift in certain risk factors? The study does not provide data on this.
Trend 2 – Increase among younger people: The trend among younger people is the opposite and quite worrying. In 2012-2013, the rectal cancer incidence of those aged 50-54 years has approached that of those aged 55-59 years, whereas previously, in 1989-1990, it was at half the level. In colon carcinoma, a similar development is found, albeit somewhat weakened – as can also be observed elsewhere.
Among Americans aged 20-39 years, incidence rates of colon cancer increased between 1% and 2.4% annually since the mid-1980s, and among those aged 40-54 years, they increased by 0.5% to 1.3% since the mid-1990s. This compares with a drop in rates among under-50s in the decade before and the early 1980s. The later increases in this group were mainly due to tumors of the distal colon.
In contrast, as mentioned, rectal cancer incidences have been rising for a longer time and also at a much steeper rate, especially in young individuals between 20 and 29 years of age. In the study period from 1974 to 2013, annual increases of about 3% were found – from 1980, this also applies to 30- to 39-year-olds.
Young have greater risk
The age-specific relative risk decreased steadily in the 1890-1950 birth cohorts, whereas it increased steadily in the 1990s birth age cohort. Accordingly, individuals who had approx. born in 1990 have a more than twofold increased risk compared to the 1950 generation of being diagnosed with colon cancer and even fourfold increased risk of being diagnosed with rectal cancer (IRR 2.40, 95% CI 1.11-5.19 and 4.32, 95% CI 2.19-8.51, respectively).
The confidence intervals are larger here because, overall, very young people naturally still fall ill much less frequently than older people and thus form a statistically smaller group. However, they are also screened less frequently, which means that carcinomas are more often already present at diagnosis and explains the increased risk. One could also argue the other way around and interpret the rates as an expression of a functioning screening. In this understanding, subclinical early carcinomas would also be detected more frequently in very young individuals, which would otherwise go unnoticed and thus underdiagnosed. However, this is unlikely, say the authors, because then the incidence rates of early stages of carcinoma would have had to increase unilaterally over advanced stages in recent years, which has been shown not to be the case [1].
Another reason could be changing lifestyle habits. Although alcohol and tobacco consumption tended to decline over the long term in the young U.S. generation [2], the authors note, obesity is also increasingly common in this group [3]. The latter is an important risk factor for colorectal cancer, which is also usually associated with other relevant and independent risk factors such as an unhealthy, unbalanced diet and little exercise.
Doctors in duty
The authors note that today’s younger generation is in similar risk ranges as people born in 1890. This means that the risk situation has deteriorated again compared with generations from the first half of the 20th century. It is now up to further studies to determine whether inadequate screening or changes in risk factors are responsible for this renewed increase.
In any case, physicians would need to be aware of the increasing likelihood of disease in the under-55 age group and take active precautions, which would also mean following screening recommendations more closely. These provide for screening examinations in those under 50 years of age in cases of high family burden or (personal) history of polyps, among others. He also said that the under-55 age group is still under-screened, even though it is clearly recommended for patients 50 years and older at intermediate risk. Most colorectal cancers develop from adenomas that undergo malignant transformation through numerous mutations over a latency of about ten years, making consistent early initiation of screening doubly useful, according to the authors.
The younger population in particular has long had poorer access to the U.S. healthcare and insurance system, which could now improve with the Affordable Care Act (ACA) – if it is not repealed.
Source: Siegel RL, et al: J Natl Cancer Inst 2017; 109(8): djw322.
Literature:
- Siegel RL, Jemal A, Ward EM: Increase in incidence of colorectal cancer among young men and women in the United States. Cancer Epidemiol Biomarkers Prev 2009 Jun; 18(6): 1695-1698.
- Ezzati M, Riboli E: Behavioral and dietary risk factors for noncommunicable diseases. N Engl J Med 2013 Sep 5; 369(10): 954-964.
- Lee JM, et al: Getting heavier, younger: trajectories of obesity over the life course. Int J Obes (Lond) 2010 Apr; 34(4): 614-623.
InFo ONCOLOGY & HEMATOLOGY 2017; 5(3): 4.
