Summary

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The Human Development Index (HDI), with a four-tier categorization of countries as having low, medium, high, or very high HDI, provides a useful framework for assessing the global cancer burden geographically and over time.

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The average HDI values at the country level can be linked to the corresponding scale and profile of cancer to document the effect of transitions towards higher HDI levels, and this can serve as evidence for national cancer control priorities. Similar linkages to risk factors and cancer-related outcomes can help to further explain transitions and inequalities in the cancer burden.

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A high residual burden of infection-related cancers is observed in countries with low HDI. Several countries with medium and high HDI, which are often undergoing major social and economic transitions, have experienced marked declines in the burden of infection-related cancers. These declines have subsequently been offset by increasing rates of cancer types that are more frequently observed in industrialized countries.

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The predicted global cancer burden is expected to exceed 27 million new cancer cases per year by 2040, a 50% increase on the estimated 18.1 million cancers in 2018. The estimated increases in the cancer incidence burden from 2018 to 2040 using demographic changes will occur in all countries, but the predicted increases will be proportionately greatest in countries with low and medium HDI.

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Human development plays a critical role in understanding the shifting scale and profile of cancer globally. However, using the four-tier HDI to describe transitions has limitations, given that it de-emphasizes the diversity of cancer occurrence and can oversimplify the multifactorial influences, including sex, ethnicity, and cultural aspects, on a complex set of diseases.

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Although attention has been drawn to broad patterns of cancer incidence according to human development level, there are clear examples of national and regional cancer diversity of cancer occurrence that depart from this model. Also, because HDI indicates national averages, it does not reflect any inequalities in human development within countries.

Epidemiological transitions in cancer

Omran’s theory of epidemiological transition described how changing health and disease patterns are influenced by demographic, economic, and societal factors [1]. In particular, Omran described how, in the third stage of the transition, infections become less important and chronic diseases become more important as the major causes of morbidity and mortality as life expectancy increases to more than 70 years and mortality – from “degenerative diseases” – is delayed. This late stage of the transition corresponds with the current rising prominence of noncommunicable diseases, which in the past decades have surpassed communicable diseases as the leading causes of death worldwide [2].

Among noncommunicable diseases, cancer has emerged as a particularly important health concern. Cancer is the first or second leading cause of premature mortality (i.e. deaths at ages 30–69 years) in more than 90 countries worldwide (see Chapter 1.1). An estimated 18.1 million new cancer cases and 9.6 million cancer-related deaths occurred worldwide in 2018, and 1 in 8 men and 1 in 10 women are likely to develop the disease during their lifetimes [3]. When coupled with the estimated cost of cancer care of US$ 1.16 trillion per year [4], this clearly makes cancer a public health priority. As a result, there has been a growing recognition of the need for action to reduce the cancer burden. This is exemplified by the World Health Assembly resolution on cancer prevention and control, which was adopted unanimously by WHO Member States in May 2017 [5].

Although cancer was once considered to be a disease of rich people and of the highest-income countries, it is now a global problem that affects all countries. The increasing magnitude of the cancer burden is in part a consequence of declining fertility and increasing life expectancy, but it is also the result of societal, economic, and lifestyle changes associated with globalization.

In this chapter, the impact of transitions in human development on cancer occurrence worldwide is illustrated by the profound effects on the patterns and trends of cancer incidence, mortality, and prevalence at the national, regional, and global levels. The predicted increases in the cancer burden will be proportionately greatest in countries in transition towards higher levels of human development. Such findings have major implications for public health and cancer control planning, and therefore should alert the global community to the growing cancer burden and the need for action, particularly in countries that are currently ill-equipped to deal with the expected escalating numbers of cancer patients in coming decades.

The Human Development Index

Human development focuses on two core dimensions: (i) directly enhancing human abilities, and (ii) creating conditions for human development [6]. Like the previous two chapters, this chapter uses the Human Development Index (HDI), a summary measure developed by the United Nations Development Programme. HDI is an indicator of national achievement in attaining a long and healthy life (based on life expectancy at birth), acquiring knowledge (based on average and expected years of schooling), and achieving a decent standard of living (based on gross national income per capita) [7]. HDI values range from 0 to 1; lower values indicate the least developed countries in terms of human development, and higher values indicate the most developed countries. Values are commonly presented, as in this chapter, according to four tiers of HDI (low, medium, high, and very high HDI), using the pre-defined cut-off points of the United Nations Development Programme. Because HDI is a composite indicator of national averages, it does not reflect any inequalities in human development within countries.

The global map of countries according to the HDI tiers is shown in Fig. 1.3.1. The low HDI tier includes countries that are largely concentrated in sub-Saharan Africa, although several countries in this region have now transitioned to the medium HDI level. The countries in the high and very high HDI tiers are geographically diverse, spanning across continents, although the very high HDI tier remains closest to the traditional view of “developed” countries in that it includes Europe and North America, Japan, and Australia and New Zealand. The very high HDI tier also includes several countries in Asia, the Eastern Mediterranean region, and South America. Most the world’s population live in countries in the medium (36.2%) and high (32.3%) HDI tiers, followed by the very high (18.0%) and low (13.5%) HDI tiers.

Fig. 1.3.1

Global map of the development levels of individual countries according to the four-tier Human Development Index (HDI), in 2015.

Cancer burden by HDI level in 2018

When the cancer burden in 2018 was assessed by the four-tier HDI, a stepwise increase in the number of new cancer cases and in the age-standardized incidence rates was evident with each increase in HDI level (Fig. 1.3.2). In 2018, 45% of the estimated new cancer cases occurred in countries with very high HDI, compared with 36%, 16%, and 4% in countries with high, medium, and low HDI, respectively. In contrast, the greatest number of cancer deaths occurred in countries with high HDI, driven by the 2.9 million cancer deaths that occurred in China. Age-standardized incidence rates indicate a slightly different pattern, in which countries in the low and medium HDI tiers have comparable burdens, although the burden is slightly higher in the low HDI tier. For age-standardized mortality rates, no correlation with HDI level is observed.

Fig. 1.3.2

The total burden of new cancer cases and cancer deaths (above) and the corresponding age-standardized (World) incidence and mortality rates per 100 000 person-years (below) for each Human Development Index (HDI) tier, in 2018.

The age-standardized incidence and mortality rates for the top 15 cancer types in 2018 for each sex are shown in Fig. 1.3.3, which compares the burden in countries with high or very high HDI with that in countries with low or medium HDI. With the exception of rates of a few cancer types, the incidence rates were generally greater in countries with higher HDI; the age-standardized incidence rates in many of these countries were 2–3 times those in countries in transition towards higher HDI levels.

Fig. 1.3.3

Bar charts of age-standardized (World) incidence and mortality rates per 100 000 person-years for the top 15 cancer types in 2018 in countries with high or very high Human Development Index (HDI) compared with countries with low or medium HDI, (more...)

In contrast, the mortality rates were broadly comparable between the two groups of countries. For some cancer types, such as breast cancer and ovarian cancer, the mortality burden was greater in countries with low or medium HDI, although the incidence rates in those countries were lower than the rates in countries with high or very high HDI. The proportionately higher case fatalities in countries with low or medium HDI relates to the poorer survival prospects after diagnosis on average, for reasons that include a lack of access to timely diagnosis and treatment. For example, when the mortality-to-incidence ratio is used as a proxy of survival, the case fatality for breast cancer is 48% in countries with low or medium HDI, 4 times that in countries with high or very high HDI.

Cancer profile by HDI level in 2018

Cancer profiles by HDI level differ when assessed by incidence, mortality, and 5-year prevalence.

In women, the five major cancer types accounted for more than 50% of the burden in each of these three indicators (Fig. 1.3.4). Uniquely, breast cancer was the most common cancer type across all HDI tiers in terms of incidence, followed by cervical cancer in the low and medium HDI tiers and colorectal cancer in the high and very high HDI tiers.

Fig. 1.3.4

The five leading cancer types in terms of incidence, mortality, and 5-year prevalence for each Human Development Index (HDI) tier in women in 2018.

Cervical cancer was the most common cause of cancer mortality in the low HDI tier and the second most common in the medium HDI tier, highlighting a residual burden of infection-related cancers in countries in these tiers. In contrast, in both the high and very high HDI tiers, infection-related cancers (see Chapter 2.2) have been displaced by lung cancer, breast cancer, and colorectal cancer; these cancer types, which are associated with behaviours and lifestyles that are more typical of industrialized societies, have become the leading causes of cancer mortality in the high and very high HDI tiers.

In women, the 5-year prevalence burden in each HDI tier generally had a similar profile of cancer types to that observed for incidence.

In 2018, the cancer profile by HDI level varied more substantially in men than in women. In men, the top five cancer types were different in each HDI tier (Fig. 1.3.5). In terms of incidence, lung cancer was the most common type in the medium and high HDI tiers, whereas prostate cancer was the most common type in the low and very high HDI tiers; this pattern may relate to ethnic and underlying genetic predispositions in the low HDI tier and to prostate-specific antigen (PSA)-related diagnosis of latent cancers in the very high HDI tier. Although the burden of infection-related cancers, such as liver cancer and Kaposi sarcoma, is higher in countries in transition, there remains a large burden of liver cancer in the high HDI tier; this is due to the nearly 393 000 new cases in China in 2018, which accounted for 84% of the liver cancer cases in the high HDI tier.

Fig. 1.3.5

The five leading cancer types in terms of incidence, mortality, and 5-year prevalence for each Human Development Index (HDI) tier in men in 2018.

Prostate cancer was the leading cause of cancer mortality in the low HDI tier, whereas lung cancer was the leading cause in the medium, high, and very high HDI tiers. Liver cancer and colorectal cancer were also among the most common causes of cancer mortality in all four HDI tiers. The cancer types contributing to the remaining mortality burden varied by HDI level.

In men, the 5-year prevalence burden in each HDI tier had a similar profile of cancer types to that observed for incidence, except that the ranking was higher for cancer types associated with better survival prospects after diagnosis.

Future cancer burden by HDI level

The predicted global cancer burden is expected to exceed 27 million new cancer cases per year by 2040, a 50% increase on the estimated 18.1 million new cancer cases in 2018. Although the predicted cancer incidence burden is highest in countries with high and very high HDI, the predicted increases will be proportionately greatest in countries with low and medium HDI: the estimated increase from 2018 to 2040 using demographic changes alone is 100% for the low HDI tier and 75% for the medium HDI tier (Fig. 1.3.6).

Fig. 1.3.6

The estimated number of new cancer cases in 2018 and the predicted increase in the number of new cancer cases from 2018 to 2040, assuming only a demographic effect, by Human Development Index (HDI) tier.

Because countries with low and medium HDI levels are currently the least equipped to deal with the impending increase in the cancer burden, these findings underscore the necessity for investment in targeted, resource-dependent, effective, and cost-effective interventions that can reduce the burden of the disease [5,8].

Cancer risk factors by HDI level

Despite the broad associations between cancer and HDI described above, there remain a large number of carcinogenic hazards, including tobacco use and alcohol consumption [9,10], infectious agents [11], obesity [12], diet [13–15], radiation [16], solar radiation [17,18], and air pollution [19,20]. Of these, obesity and infectious agents are particularly interesting to examine according to HDI, because of their relative importance in the cancer burden in countries with higher HDI (obesity) and lower HDI (infectious agents).

Obesity

Excess body fatness (see Chapter 2.7) is considered to cause the following cancer types: cancers of the oesophagus (adenocarcinoma), gastric cardia, colon and rectum, liver, gall bladder, pancreas, breast (in postmenopausal women), endometrium, ovary, kidney (renal cell carcinoma), and thyroid, and meningioma and multiple myeloma [12]. When the relationship between excess weight – or obesity – and cancer was assessed by HDI, the attributable fractions in countries with very high and high HDI (~5% each) were 2–3 times those in countries with medium HDI (1.6%) or low HDI (1.0%) [21]. When the relationship was assessed by sex, the number of cancer cases attributable to obesity was observed to increase with HDI level in both men and women (Fig. 1.3.7).

Fig. 1.3.7

The number of cancer cases attributable to high body mass index (BMI) and the number of preventable cancers if BMI scores remained the same in 2012 as in 1982, by sex and Human Development Index (HDI) tier.

When the number of preventable cancers was assessed, the number increased with HDI level in men. This relationship was less consistent in women; the number of preventable cancers was greatest in the very high and medium HDI tiers [21]. Therefore, although prevention programmes that seek to control weight gain are clearly needed in the most developed countries, these findings also emphasize the need for a global effort to reduce the number of people with high body mass index, because the continuation of current patterns of population weight gain will increase the future cancer burden across all HDI tiers [21].

Cancer outcomes by HDI level

Given that cancer contributes substantially to morbidity and mortality globally, it is important to assess the implications of cancer and the extent of cancer-related sequelae. To determine the impact of fatal and non-fatal cancer outcomes, disability-adjusted life years (DALYs) are often used as a measure. DALYs combine the degree of illness and disability in patients and long-term survivors (years of healthy life lost due to disability [YLD]) and the burden of cancer mortality (years of life lost due to premature mortality [YLL]), to quantify the number of years of healthy life lost.

Soerjomataram et al. assessed DALYs globally by the four-tier HDI and found the total DALYs to be similar across HDI tiers (Fig. 1.3.8) [23]. However, the contribution of YLL and YLD to the total DALYs varied substantially by HDI tier: in general, the number of years lived with disability (YLD) was greater in countries with higher HDI levels, and the burden of premature mortality (YLL) was greater in countries with lower HDI levels.

Fig. 1.3.8

Age-adjusted disability-adjusted life years (DALYs) per 100 000 population by Human Development Index (HDI) tier for all cancer sites combined and selected cancer sites. YLD, years of healthy life lost due to disability; YLL, years of life lost (more...)

The relationship between DALYs and HDI level varied depending on the cancer site being assessed. In particular, for cancer types more commonly attributable to obesity (e.g. breast cancer and colorectal cancer), DALYs were greater in countries with higher HDI levels, whereas for infection-related cancer types (e.g. cervical cancer and liver cancer), DALYs were greater in countries with lower HDI levels [23]. YLL was consistently the main contributor to DALYs across HDI tiers, but the fraction of DALYs due to YLL in the lowest HDI tier was generally the same as or larger than the fraction in the highest HDI tier, reflecting the poorer average prognosis of patients with cancer in low-resource settings.

In another study, the impact of cancer on changes (increases or decreases) in life expectancy was assessed worldwide for the period 1981–2010 [24]. The findings suggested that countries with very high HDI had larger gains in life expectancy compared with countries with medium or high HDI. In particular, declines in cancer mortality were responsible for the increases in life expectancy for individuals aged 40–84 years by 0.8 years for men and 0.5 years for women in countries with very high HDI, whereas the corresponding gains were less in countries with medium or high HDI: 0.2 years for both men and women [24].

Similar inequalities in life expectancy gains were observed for the hypothetical situation of eliminating all deaths from cancer. The resulting increase in life expectancy for individuals aged 40–84 years for the period 2006–2010 was 2.5 years for men and 1.9 years for women in countries with very high HDI, whereas the increases were only modest in countries with medium or high HDI: 1.6 years for men and 1.5 years for women [24]. These results provide evidence of disproportionate improvements in cancer outcomes according to HDI level, leading to widening gaps in life expectancy between more-developed and less-developed countries.

Evidence of diversity within HDI levels

Evidently, the marked differences in the scale and profile of cancer incidence and mortality by HDI level result from a myriad of factors, which will dictate whether, in the longer term, gains in societal and economic development will reduce the widening gap between countries with low versus very high HDI in the risk of developing or dying from cancers that are preventable or treatable. Some of the determinants are systems-related, including the extent to which cancer control initiatives are implemented, and others link to risk directly, such as the changing prevalence and distribution of specific reproductive, dietary, and metabolic factors.

Using the four-tier HDI to describe transitions has limitations, given that it de-emphasizes the diversity of cancer occurrence worldwide and the extent to which it varies between and within countries. Although attention has been drawn to broad patterns of cancer incidence according to human development level, there are clear examples of national and regional diversity of cancer occurrence that depart from this model.

For example, although there have been systematic declines in cervical cancer incidence rates in countries with medium or high HDI, the 40-year trends in incidence rates indicate recent increases in countries with high or very high HDI (e.g. Belarus and Japan) (Fig. 1.3.9). Such increases are likely to be due to changes in sexual behaviour that, in the absence of effective screening programmes, have led to an increasing risk of persistent infection with high-risk HPV subtypes and subsequent increases in the occurrence of cervical cancer (see Chapter 1.2).

Fig. 1.3.9

Age-standardized (World) incidence rates per 100 000 person-years for cervical cancer by calendar year in selected countries with high and very high Human Development Index (HDI) levels, circa 1975–2012. Asterisks indicate regional registries (more...)

Conclusions

Despite inherent diversity in the cancer burden within a given HDI level, HDI provides a useful framework to map out continuing transitions in cancer incidence, risk factors, and outcomes. In particular, HDI serves as an exploratory tool to monitor shifts in the profile of cancer types, as clearly demonstrated by the displacement of infection-related cancers by cancers associated with behaviours and lifestyles that are more typical of industrialized societies, and with increasing societal and economic development.

Although the cancer incidence burden is currently highest in countries with very high HDI, the predicted increases in the cancer burden will have the greatest impacts on countries with low and medium HDI. Because cancer outcomes are already poorer in countries in transition, appropriate scaling up of resources for effective strategies in primary and secondary prevention in these countries is critical to effectively control the prevalence of adverse lifestyle factors, to ultimately reduce the cancer burden.

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