Series
Global cancer patterns: causes and prevention
Introduction
We have three main goals in this Series paper: to show that cancer is a global problem, although not a uniform one, with an increasing proportion of the burden falling on low-income and middle-income countries; to describe some of the successes and failures in addressing of cancer prevention at a population level; and to argue that primary prevention is a particularly effective approach to tackle the impending increases in cancer on a global scale. We limit our focus to primary prevention, and only tangentially discuss early detection and screening, albeit recognising that primary prevention should be a complement to secondary prevention and treatment in overall cancer-control strategies. We make these points in view of the political focus on the control of non-communicable diseases (NCDs) after the high-level meeting of the UN General Assembly in September, 2011.1
One strong argument in favour of primary prevention is that the cause could be removed or greatly reduced in the long term. This potential is especially important when resources are scarce, and represents a marked distinction from early detection, screening, and therapies. Primary prevention might also have an effect for people other than those who are directly targeted by it. A typical instance is herd immunity, in which vaccination can prevent the disease in many more individuals than only those vaccinated. Similarly, banning of smoking in public places has a positive effect not only on the target population—those potentially exposed to second-hand smoke—but also on smokers, who will tend to smoke less, or quit.2 This situation is less evident with therapies or screening, when inclusion of many individuals is generally necessary for preventive success,3 although wider benefits of screening could result from increased awareness in a population, and the potential for such collateral benefits merits assessment. Additionally, primary cancer prevention can have benefits in addition to those for cancer, in view of the shared risk-factors with several other NCDs.
Section snippets
Globalisation of cancer
The Human Development Index (HDI) is a useful classifier for the globalisation of cancer,4 because it takes into account education and life expectancy as well as national income, with countries categorised into one of four levels of development: low, medium, high, and very high. Although communicable diseases and nutrition-related disorders are still the most common causes of death in low-HDI countries, they are projected to be overtaken by NCDs, including cancer, by 2030.5 The projected
Global patterns and mortality
In 2008, 28·8 million people globally were estimated to be within 5 years of being diagnosed with cancer, with close to half of these living in very high HDI countries, which comprise only a sixth of the world's population.8 By contrast, the 3·4 billion people living in low-HDI and medium-HDI countries have only slightly more than a third of the global cancer prevalence (10·8 million cases). This disparity is due to two components: higher rates of newly diagnosed cancers in the high-HDI and
Cancer transition: time trends
Time trends in cancer incidence and mortality vary substantially for different cancers and countries.4 The cancer transition in low-HDI countries combined with growing and ageing populations means that many countries are facing a double burden of cancer—ie, the burden associated with infectious agents combined with that associated with an increasingly westernised lifestyle.
The situation in high-income countries is more nuanced. On the one hand, some countries have encouraging trends for
What are the major risk factors for cancer?
The WHO Global Status Report on NCDs addresses several risk factors for cancer, including tobacco use, alcohol consumption, little physical activity, and unhealthy diet.26 However, cancer is far more heterogeneous than are other NCDs, and needs a nuanced and geographically-specific policy, rather than a generalised one focusing on a narrow set of shared personal and behavioural risk factors.1 A prime example is chronic oncogenic infections, which cause an estimated 16% of cancers globally but
Causes of causes
Tackling of the worldwide NCDs epidemic will be impossible if prevention is limited to promotion of health behaviours at the individual level. Low physical activity, for example, is closely associated with changes in living conditions that promote or facilitate a sedentary behaviour—the so-called built environment.76 Additionally, the quality of food consumed is associated with income and education and is being driven by availability and industry marketing. Economic growth in low-HDI countries
An overall estimate of preventable cancers
Genetic variants are unlikely to account for a major proportion of cancer cases; 5–10% are attributable to highly penetrant mutations such as in BRCA1 or mismatch repair genes, and an unknown proportion to the interaction between low-penetrant variants and external risk factors. For a long time, since the publication of Doll and Peto's The causes of cancer83 containing estimates for the USA, the proportion of cancers in a population that is attributable to known risk factors has been a
Conclusions
Cancer is a global and growing, but not uniform, problem. We have argued that primary prevention is an especially effective—and probably also cost-effective—way to fight cancer, with between a third and a half of cancers being preventable, on the basis of present knowledge. If complemented by earlier detection and more effective treatment, cancer control would progress markedly. However, present social and economic trends do not promote prevention. The benefits of prevention take time to
References (93)
- et al.
Global cancer transitions according to the Human Development Index (2008–2030): a population-based study
Lancet Oncol
(2012) - et al.
A global view on the development of non communicable diseases
Prev Med
(2012) - et al.
Tobacco use in 3 billion individuals from 16 countries: an analysis of nationally representative cross-sectional household surveys
Lancet
(2012) - et al.
Poverty, obesity, and malnutrition: an international perspective recognizing the paradox
J Am Diet Assoc
(2007) - et al.
Cancer survival in Africa, Asia, and Central America: a population-based study
Lancet Oncol
(2010) - et al.
Expansion of cancer care and control in countries of low and middle income: a call to action
Lancet
(2010) - et al.
Status of radiotherapy resources in Africa: an international atomic energy agency analysis
Lancet Oncol
(2013) Breast-cancer early detection in low-income and middle-income countries: do what you can versus one size fits all
Lancet Oncol
(2011)- et al.
The global epidemiology of hepatocellular carcinoma: present and future
Clin Liver Dis
(2011) - et al.
Liver cirrhosis mortality rates in Britain from 1950 to 2002: an analysis of routine data
Lancet
(2006)