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World Cancer Report

Highlights


Although excess body fatness increases the risk of cancers at various organ sites, including the colon and rectum, the risk may be reduced by intentional weight loss.

In assessing cancer risk, World Cancer Report specifies

Strong epidemiological evidence exists that being physically active reduces the risk of cancers of the bladder, breast, colon, endometrium, kidney, oesophagus, and stomach. Emerging evidence suggests that sedentary behaviour is associated with an increased risk of cancers of the breast, colon, endometrium, and lung.

Strong evidence exists for an association between obesity and increased risk of cancers of the postmenopausal breast, colorectum, endometrium, kidney, liver, oesophagus, and pancreas, and moderate evidence exists for an association with cancers of the gall bladder, mouth, pharynx, larynx, ovary, prostate (advanced), and stomach.

Progressing from these findings to preventive intervention, research documented in World Cancer Report includes

There is now clear evidence that the greatest change in diet and physical activity across a population can be achieved when population-wide approaches, such as policy specification, are combined with individually targeted approaches. Approaches to changing diet and physical activity should take into consideration health-enhancing environments, behaviour change communications, and systems change.

Cancer-causing pollution of air and water are amenable to intervention by technological and regulatory means.

In assessing cancer risk, World Cancer Report specifies

Air pollution, both outdoor and indoor, is the most widely investigated and most important contributor to the environmental cancer burden in human populations. Air pollution alone was responsible for an estimated 350 167 deaths from lung cancer worldwide in 2017.

Drinking-water, or water used for agricultural or recreational activities, can be polluted by naturally occurring carcinogenic contaminants, such as arsenic, or by anthropogenic pollutants, including chlorinated agents, perfluorinated alkylated substances, and metals. Water pollution can be due to leaks from contaminated soils, and can result in contamination of the food chain.

Progressing from these findings to preventive intervention, research documented in World Cancer Report includes

The prevention of exposure to carcinogenic environmental pollutants requires both regulatory action and community commitment. At the global level, the situation is currently improving in high-income countries and worsening in low- and middle-income countries.

Governmental action has been effective in reducing exposure to known and suspected carcinogens. These actions can involve legislation, regulation (to eliminate or restrict exposure), enforcement of legislation and regulations, voluntary (non-enforceable) guidelines, incentives, and education campaigns. Depending on the legal authority, the basis of regulation can be hazard, exposure, or risk.

Cervical cancer may be eliminated as a public health problem by vaccination against human papillomavirus (HPV) infection, even in low-income countries where cervical cancer is the major cancer type.

In assessing cancer risk, World Cancer Report specifies

Thirteen sexually transmitted mucosal human papillomavirus (HPV) subtypes are established human carcinogens. Together, they are responsible for all cervical cancer cases globally (570 000 cases) and a variable proportion of cases of other anogenital and oropharyngeal cancers (totalling 120 000 cases).

The essential molecular interactions of the different HPV oncoproteins to induce cervical carcinogenesis are now better understood.

Progressing from these findings to preventive intervention, research documented in World Cancer Report includes

Comprehensive data document the safety and high efficacy of HPV vaccines, especially in adolescent girls, who are the priority target for HPV vaccination.

Three prophylactic vaccines, consisting of empty viral capsids of HPV types 16 and 18, alone or with an additional two or seven types, have been available since 2006. By 2018, 85 countries had established HPV vaccination programmes.

Anti-vaccination campaigns and the relatively high cost, coupled with the necessarily protracted time frame to cancer prevention, hamper adequate coverage and universal implementation of HPV vaccination.

Deaths from sporadic cancers (i.e. cancers for which no recognized exposure accounts for tumour development) may be prevented by screening or earlier diagnosis.

In assessing cancer risk, World Cancer Report specifies

Multiple factors are recognized as contributing to the development of sporadic cancers.

Cancer stem cells are a selective clonal subset of tumour cells that have avoided various cell regulatory mechanisms, including terminal differentiation, and yet have retained the self-renewal properties and proliferative potential of adult stem cells.

Progressing from these findings to preventive intervention, research documented in World Cancer Report includes

Early detection of cancer is a critical component of cancer control. In addition to reduction of mortality from a specific cancer type, a proper approach to cancer screening should ensure that the harms do not outweigh the benefits.

The analysis of tumour-derived products, including circulating cell-free tumour DNA and related biomarkers, in body fluids is increasingly recognized as an aid in the early diagnosis of malignant disease.

Progress in technology, such as next-generation sequencing, is paving the way for the development of diagnostic tests for early detection of cancer and the introduction of precision medicine into clinical practice.

In diverse countries, socioeconomic disparities limit the impact of proven preventive interventions.

In assessing cancer risk, World Cancer Report specifies

Within countries, the socioeconomic gradient for cancer incidence may vary in magnitude and direction across different cancer sites, but cancer mortality is often higher, and cancer survival lower, in groups with low socioeconomic position and other disadvantaged groups, such as ethnic and racial minorities and Indigenous populations, for cancer overall and for the large majority of cancer types.

In sub-Saharan Africa, the poverty rate (a deprivation level measuring the proportion of the population living in extreme poverty) was a strong predictor of cross-national variations in cervical cancer incidence and mortality.

Differences in lifestyles and dietary patterns between urban and rural communities are becoming more pronounced along with rapid economic development, urbanization, and the ageing of the population. These could partly explain the urban–rural difference in the spectrum of cancer types in China.

Among people with lower socioeconomic status in India, non-awareness of the harms of tobacco use in any form and of chewing products that contain areca nut is common, as is inadequate comprehension of the associated health risks.

Progressing from these findings to preventive intervention, research documented in World Cancer Report includes

Given the focus of primary prevention on health literacy, awareness, and behaviour change, addressing the socioeconomic determinants that influence these factors is critical to advance cancer prevention.

Even in high-income countries, socioeconomic disparities limit the impact of proven preventive interventions.

In assessing cancer risk, World Cancer Report specifies

Basic differences are evident between screening practices followed in European Union countries, including the target age ranges for screening, the interval between screening tests, and the screening procedures used.

In the USA, persistent disparities in health, health services, and health outcomes are associated with race and ethnicity, sexual and gender minority status, lower education level, lower income, lack of health insurance, lower health literacy, lower access to health services, low-quality health services, distance from health services, rural residence, and racial segregation.

Low-quality care also may be influenced in the USA by implicit racial and class bias, which reflects automatic and unconscious negative attitudes towards low-income and minority groups and has been shown to negatively influence patient communication, clinical care, and cancer outcomes.

Progressing from these findings to preventive intervention, research documented in World Cancer Report includes

Research shows that achieving relatively high participation rates in cancer screening in the European Union will reduce health inequalities. In patients with breast cancer, screen detection is an independent favourable prognostic factor.

Disparities in access to cancer prevention and early detection and in cancer incidence and mortality in the USA can be reduced by a combination of national policies and local initiatives that remove barriers to care.

Individual susceptibility to particular cancers is increasingly understood from molecular technology.

In assessing cancer risk, World Cancer Report specifies

Genome-wide association studies (GWAS) have accelerated the pace of discovery of common genetic susceptibility variants. More than 85% of the loci identified in cancer GWAS have been discovered in individuals of European ancestry, with approximately 10% in Asian ancestry and less than 5% in African ancestry; this reflects the scope of studies undertaken to date.

Epigenetic events are intimately associated with fetal organ development, pathological events associated with ageing, biochemical effects of micronutrients, and the tumorigenic effects of cytokine mediators of chronic inflammation. The proposed tumorigenic event is a polyclonal epigenetic disruption of stem/progenitor cells mediated by aberrant regulation of tumour progenitor genes.

Progressing from these findings to preventive intervention, research documented in World Cancer Report includes

Although the pace of discoveries from GWAS has accelerated with large collaborative networks, the investigation of each individual susceptibility locus has not advanced at a comparable speed.

Landscape analyses of events across entire cancer genomes have revealed a wide range of types of somatic genetic events (from single base mutations to the shattering of entire chromosomes), many involving driver genes, and even more mutations that appear to be passengers.

The density of single-nucleotide mutations across a genome differs by nearly 4 orders of magnitude (> 10 000-fold) between cancer types with strong environmental factors and tumours with little such evidence, such as paediatric cancers.

Protective actions are being taken against hazardous exposure to sunlight.

In assessing cancer risk, World Cancer Report specifies

The highest incidence rates of skin cancer are observed in the predominantly fair-skinned populations living in areas with very high ambient levels of solar radiation, such as Australia and New Zealand.

Ultraviolet radiation directly and indirectly induces DNA lesions, which cause mutations and trigger inflammation and immunosuppression, which mediate skin cancer growth. Both ultraviolet radiation itself and ultraviolet-induced inflammation lead to the generation of reactive oxygen species. These reactive oxygen species also cause DNA lesions and increase the frequency of mutations. Furthermore, lipid peroxidation caused by ultraviolet radiation and reactive oxygen species also contributes to immunosuppression.

Genes critical for melanoma development, which often have ultraviolet radiation-induced mutation, include genes that control cell proliferation (e.g. BRAF), cell cycle and replication (e.g. TP53), and metabolic pathways.

Progressing from these findings to preventive intervention, research documented in World Cancer Report includes

The most effective way to reduce skin cancer incidence is to avoid unnecessary sun exposure, use protective measures when in the sun, and avoid tanning devices.

Since 2007, the incidence of melanoma has been declining overall in Australia, driven largely by significant reductions in recent birth cohorts, consistent with a successful intervention to reduce sun exposure.

Tobacco use continues to be a major cause of cancer worldwide.

In assessing cancer risk, World Cancer Report specifies

Tobacco products have been studied for decades and are well known to cause cancer. Nevertheless, with larger epidemiological studies, longer follow-up, and better control for confounding, the number of types or subtypes of cancer known to be caused by tobacco products continues to increase.

Worldwide, most tobacco is now consumed in low- and middle-income countries in the form of smoked products, chiefly as manufactured or hand-rolled cigarettes.

Both smoked and smokeless products are widely used in South-East Asia.

Progressing from these findings to preventive intervention, research documented in World Cancer Report includes

Progress in tobacco control is notable but far from sufficient. Worldwide, an estimated 2.4 million tobacco-related cancer deaths occur per year.

Lung cancer in never-smokers is a specific disease entity.

Lung cancer screening by low-dose computed tomography in high-risk populations represents an opportunity for mortality reduction, but its efficiency will be improved by individual risk prediction.



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