The rising tide of early-onset colorectal cancer: a comprehensive review of epidemiology, clinical features, biology, risk factors, prevention, and early detection

Colorectal cancer (CRC) is a frequently lethal disease with heterogeneous outcomes and drug responses. To resolve inconsistencies among the reported gene expression–based CRC classifications and facilitate clinical translation, we formed an international consortium dedicated to large-scale data sharing and analytics across expert groups. We show marked interconnectivity between six independent classification systems coalescing into four consensus molecular subtypes (CMS) with distinguishing features: CMS1 (MSI Immune, 14%), hypermutated, microsatellite unstable, strong immune activation; CMS2 (Canonical, 37%), epithelial, chromosomally unstable, marked WNT and MYC signaling activation; CMS3 (Metabolic, 13%), epithelial, evident metabolic dysregulation; and CMS4 (Mesenchymal, 23%), prominent transforming growth factor β activation, stromal invasion, and angiogenesis. Samples with mixed features (13%) possibly represent a transition phenotype or intra-tumoral heterogeneity. We consider the CMS groups the most robust classification system currently available for CRC – with clear biological interpretability – and the basis for future clinical stratification and subtype–based targeted interventions.

Globally, colorectal cancer (CRC) is the third most commonly diagnosed malignancy and the second leading cause of cancer death. Arising through three major pathways, including adenoma-carcinoma sequence, serrated pathway and inflammatory pathway, CRC represents an aetiologically heterogeneous disease according to subtyping by tumour anatomical location or global molecular alterations. Genetic factors such as germline MLH1 and APC mutations have an aetiologic role, predisposing individuals to CRC. Yet, the majority of CRC is sporadic and largely attributable to the constellation of modifiable environmental risk factors characterizing westernization (for example, obesity, physical inactivity, poor diets, alcohol drinking and smoking). As such, the burden of CRC is shifting towards low-income and middle-income countries as they become westernized. Furthermore, the rising incidence of CRC at younger ages (before age 50 years) is an emerging trend. This Review provides a comprehensive summary of CRC epidemiology, with emphasis on modifiable lifestyle and nutritional factors, chemoprevention and screening. Overall, the optimal reduction of CRC incidence and mortality will require concerted efforts to reduce modifiable risk factors, to leverage chemoprevention research and to promote population-wide and targeted screening.

Colorectal cancer (CRC) is one of the most common malignancies in the United States. Every 3 years, the American Cancer Society provides an update of CRC incidence, survival, and mortality rates and trends. Incidence data through 2013 were provided by the Surveillance, Epidemiology, and End Results program, the National Program of Cancer Registries, and the North American Association of Central Cancer Registries. Mortality data through 2014 were provided by the National Center for Health Statistics. CRC incidence rates are highest in Alaska Natives and blacks and lowest in Asian/Pacific Islanders, and they are 30% to 40% higher in men than in women. Recent temporal patterns are generally similar by race and sex, but differ by age. Between 2000 and 2013, incidence rates in adults aged ≥50 years declined by 32%, with the drop largest for distal tumors in people aged ≥65 years (incidence rate ratio [IRR], 0.50; 95% confidence interval [95% CI], 0.48-0.52) and smallest for rectal tumors in ages 50 to 64 years (male IRR, 0.91; 95% CI, 0.85-0.96; female IRR, 1.00; 95% CI, 0.93-1.08). Overall CRC incidence in individuals ages ≥50 years declined from 2009 to 2013 in every state except Arkansas, with the decrease exceeding 5% annually in 7 states; however, rectal tumor incidence in those ages 50 to 64 years was stable in most states. Among adults aged <50 years, CRC incidence rates increased by 22% from 2000 to 2013, driven solely by tumors in the distal colon (IRR, 1.24; 95% CI, 1.13-1.35) and rectum (IRR, 1.22; 95% CI, 1.13-1.31). Similar to incidence patterns, CRC death rates decreased by 34% among individuals aged ≥50 years during 2000 through 2014, but increased by 13% in those aged <50 years. Progress against CRC can be accelerated by increasing initiation of screening at age 50 years (average risk) or earlier (eg, family history of CRC/advanced adenomas) and eliminating disparities in high-quality treatment. In addition, research is needed to elucidate causes for increasing CRC in young adults. CA Cancer J Clin 2017. © 2017 American Cancer Society. CA Cancer J Clin 2017;67:177-193. © 2017 American Cancer Society.