According to the American Institute for Cancer Research, colorectal cancer (CRC) is the third most commonly diagnosed cancer in men and the second most CRC in women worldwide. In 2018 alone, approximately 1.8 million new cases of CRC were diagnosed with over 145,600 new cases occurring in the United States. Globally, the distribution of CRC burden varies widely (1). The Human Development Index (HDI) is a statistical tool to measure a country’s overall achievement in its environmental and socioeconomic growth (2). It a snapshot of human development: a long and healthy life, being knowledgeable and having a decent standard of living. A long and healthy life expectancy is measured from birth (Life Expectancy Index). Knowledge is determined by the indicators of expected and mean years of schooling (Education Index). Finally, a decent standard of living is determined by the gross national index (GNI) per capital (3). The HDI is categorized as very high (mean 0.88; 0.80–0.95), high (mean 0.76; 0.71–0.78), medium (mean 0.61; 0.56–0.70), or low (mean 0.53; 0.38–0.55) (4). The United States (HDI 0.92) trends behind many other western countries with the 9th highest incidence of CRC at 38.6 per 100,000 populations with the highest incidence occurring in Hungary and South Korea (5) (Table 1). Strikingly, cancer-related death is expected to increase by 60% by 2030 (Figure 1). Understanding the paradigm shift in the geo-demographic, socioeconomic, environmental, biogenetic distribution of CRC and the factors affecting early detection and management is paramount to identifying polices and interventions to eradicating it. The purpose of this expanded review is to address the trends and implications of CRC globally using their HDI. Ultimately, country specific resource allocation in formulating strategies in early CRC detection is fundamental in decreasing the global rise in incidence particularly among young adults.
Epidemiology and global distribution of CRC
CRC incidence and mortality rates vary widely across regions with the majority occurring in high-income (HDI) countries (6). The lowest rates are noted in Sub-Saharan Africa, except for South Africa, and Southern Asia (Figures 2,3). These global distribution and trends likely reflect changes in the prevalence of risk factors. Arnold et al. (3) noted the rise in incidence among most populations reflect lifestyle and behavioral factors including dietary patterns and obesity, whereas the mortality decline may be attributed to improvements in survival through the adoption of best practices in cancer diagnosis and treatments in developed countries.
Additionally, low and medium-income countries lack of CRC screening has significantly impacted the overall incidence and disease burden within these populations compared to high and upper-middle income countries where screening is robust. Although the risk of developing CRC increases with age, there is a unique near-global rise in incidence and mortality in early on-set CRC with a 50% increase in CRC incidence among populations younger than 50 years (Figures 4,5) (7). Epidemiologic trends predict an increase in overall crude incidence of 1% to 3% annually for adults younger than age 50 (8). This shift may represent a key to recent changes in risk factor exposures and disease pathogenesis and overall future cancer burden.
Environmental influence and socioeconomic impact on CRC risk acquisition
The gradual increase in the incidence of CRC in some low and medium HDI countries likely reflects the adoption of western lifestyles (Figure 6) (9). Among adults 50 years and older in these populations, there has been a rapid rise in the CRC incidence and mortality particularly in Eastern Europe, Asia, and South America. This is compared to very high HDI areas such as the USA, Australia, New Zealand and several Western European where the incidence and mortality have stabilized among same cohort (10) (Figure 6). Societal and socioeconomic factors appear to affect the development of CRC. In low and medium-to-high HDI countries, increased globalization and adoption of western lifestyle with its associated CRC risk factors such as obesity, lack of exercise, tobacco and alcohol use, dietary indiscretion and pollution may be the culprit. However, the stabilization and/or decline of rates in the highest indexed HDI countries, although multifactorial, may reflect early detection through screening, both invasive and non-invasive, and advanced techniques in the management of precancerous lesions as opposed to decreased in risk factors (11-13).
Pathogenetic changes and early-life exposures that influence colorectal carcinogenesis
There is mounting evidence to demonstrate the rising incidence and mortality of CRC in the previously perceived “lower risk” young adults. This effect has been demonstrated in both the US (14) and Canada (15) and now similar phenomenon across Europe and Asia (12). Modifiable known risk factors for CRC have been extensively investigated with previous epidemiological studies suggesting most predominantly alcohol consumption, diets high in red/processed meats, low fiber diet, obesity, smoking, and physical inactivity (Table 2). This certainly has been fueled by easy accessibility to readily available at-risk items particularly smoking and processed meats. Smoking alone in CRC will increase mortality by 23% and increase recurrence by 47%. Obesity certainly parallels the increase in CRC incidence in young adults and in countries with high HDI as excess diet intake may initiate a chronic low-grade inflammatory cellular response (Figure 7). According to WHO, obesity is defined by body mass index (BMI): obesity (BMI: 30.0–34.9 kg/m2) and morbidly obese (BMI ≥40 kg/m2) compared to normal weight (BMI: 18.5–24.9 kg/m2).The clinical impact of obesity on CRC appears to be more pronounced in males compared to females. Compared to normal weight individuals, the incidence of CRC has been shown to be higher in both men and women with rates of over 35% and 15% respectively (16). Weight gain and obesity appears to have a greater influence on CRC risk when it occurs in early adulthood versus later in life (17-19). Central obesity in males has been cited one of the most significant predisposing factors for CRC and worse outcome (20,21).
CRC mortality is affected by obesity as high body weight measured prior to diagnosis reduces the likelihood of CRC survival. Other factors have been purported in attempt to explain the current trend. Vuik et al. proposed the low threshold for colonoscopy for diagnostic and screening purposes may have been responsible for a proportion of the detected CRCs in young adults (22). All these proposed factors remain speculative and further investigation is required to establish causation.
Factors affecting CRC screening and early detection
The CRC transition from adenoma-carcinoma is well-established (23). The detection and removal of premalignant polyps is effective in preventing and treating cancer at an early stage both by decreasing the incidence and burden of CRC. Screening methods include stools-based testing, endoscopy, and radiographic modalities with varying degree of sensitivity and specificity. For average risk population, the United State Preventive Services Task Force (USPSTF) and the American Society for Gastrointestinal Endoscopy (ASGE), and previously American Cancer Society (ACS) recommend initial screening colonoscopy (24).
The optimal screening modality is a shared decision-making process, which incorporates individual patient preferences, values, and risk, as well as test effectiveness, resource availability, test safety, convenience, comfort, and cost. Most strategies are based either on an annual or biennial stool-based testing (FOBTs, Fecal DNA), CT colonography every five years, with optical colonoscopy reserved for positive finding requiring further investigation, or partial/complete colonic endoscopic procedures (25). Optical colonoscopy is the most preferred and accurate of all the screening methods for CRC screening. After a well-informed decision process, the best screening test is one that the patient is willing to complete according to the test instructions (26).
Studies evaluating the incidence of CRC following initial complete colonoscopy with polypectomy demonstrate significant reduction rates ranging from 76% to 90% (27,28). The National Polyp Study demonstrated a 53% reduction in CRC-related mortality after colonoscopic polypectomy (29). The screening uptake for CRC defines the cross-sectional assessment of compliance to the screening modality and according to the ACS of the average-risk population. In March 2014, the National Colorectal Cancer Roundtable (NCCRT) launched an ambitious initiative to reach an 80% CRC screening rate of eligible adults (30). If successful, an estimated 277,000 CRC cases and 203,000 CRC deaths will be prevented by 2030. In the US, the proportion of adults older than 50 years with a recent screening test ranged from 53% to 73% between 2011–2013 far below those of other recommended adult preventive services. Factors affecting CRC screening uptake include: sociodemographic factors, healthcare systems and provider factors, and psychosocial factors such as knowledge barriers, risk versus benefit perception concerns, and cultural biases (31). In a recent study from the ACS, Fedewa and colleagues evaluated CRC screening beginning at age 45. Among people ages 45 to 49, past-year CRC screening rates rose from 4.8% in the first quarter of 2018 to 6.6% in the second quarter, 8.8% in the third quarter, and 11.7% in the fourth quarter. This was accompanied by a relatively stable rate among adults over the age of 50 (32). These factors affecting the CRC screening rate may become more relevant in the at-risk younger adult population as interventions are created to address the increasing incidence of CRC. Table 3 shows the predictors of CRC non-screening rates with lack of health insurance often cited as a major predictor of non-screening. At a system-based level, implementing policies to decrease direct patient financial burden, increasing provider access, and standardizing screening modalities may improve on patient compliance and screening uptake. There has been tremendous progress in the field of medicine and despite the advancements in the world; there is still a lack of access to basic health needs and care. These are all issues that could be diminished by reducing the disparities that isolate these populations.
Some of these disparities are related to the geography and a shortage of physicians. In addition, income inequality with individuals and families simply unable to afford health care allows for the perpetuation of the process.
Global health professionals exploring opportunities to advocate for underrepresented communities in public health forums may solve these economic challenges. Encouraging physicians to practice in remote areas with incentives and introducing policies may reduce barriers and increase access to health care.
The USPSTF recommends the use of approved CRC screening methods in average-risk individuals. The ACS, based on its 2018 landmark population study, changed its CRC screening recommendation to 45 years of age. This recommendation has not been universally adopted particularly by the USPSTF. In the U.S., commercial health insurance and Medicare provide full coverage for the USPSTF approved screening modalities at the recommended age. However, there are some unique caveats that may affect screening colonoscopy coverage and subsequently influence out-of-pocket financial burden to the patient (33,34). There has been considerable effort aimed at raising CRC screening rates (35-37). Unfortunately, these initiatives and programs are only feasible in high, and some medium-HDI countries. In 2008, the International Colorectal Cancer Screening Network (ICRCSN) conducted a survey of pilot programs with organized CRC screening programs (38). In average risk individuals, stool-based test was the primary CRC screening modality, followed by FOBT and FIT tests. This was followed by colonoscopy if any of the initial screening modality was positive. This approach may help guide the development of public health policies for the early detection of CRC even in resource-limited populations. Rabeneck et al. proposed recommendations on implementing screening and diagnosis for CRC in four different resource environments (39,40) (Table 4). These recommendations, although remain to be validated, is very comprehensive and represent the basis for further research and broader implementation.
CRC remains one of the most preventable cancers worldwide with a clearly defined pathogenesis. However, it is a public health burden as it remains a commonly diagnosed cancer worldwide and one of the leading causes of cancer mortality. The incidence and mortality of CRC is decreasing in developed countries, while the incidence and mortality of this, based on trends, and has seen an increase in developing countries. Globally, there has been an exclusive increased in the incidence of CRC in young adults (<50) as opposed to stabilization or decreased among adults over the age of 50. The exact cause of these paradigm shifts is multifactorial. As has been noted, the higher incidence rates of CRC in countries with high HDI are associated with a sedentary lifestyle, obesity, diets high in red meat, and smoking. Low mortality rates in counties with low HDI may be due to low incidence of CRC or incorrect diagnosis. Identification of independent risks factors and implementation of interventions to mitigate risk factors and increase screening uptake are paramount in the prevention of CRC. The Global correlation with the incidence of CRC and the HDI is very strong. Further work needs to continue in low HDI countries for greater access to medical care and screening for CRC.
Provenance and Peer Review: This article was commissioned by the editorial office, Journal of Gastrointestinal Oncology for the series “Global GI Malignancies”. The article has undergone external peer review.
Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at http://dx.doi.org/10.21037/jgo-2019-gi-06). The series “Global GI Malignancies” was commissioned by the editorial office without any funding or sponsorship. John F Gibbs served as the unpaid Guest Editor of the series and serves as an unpaid editorial board member of Journal of Gastrointestinal Oncology from Jan 2019 to Dec 2020. The authors have no other conflicts of interest to declare.
Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.
Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.
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