Chance, choice and cause in cancer aetiology: individual and population perspectives

[Why did I get cancer?]

Two interesting papers explore the beliefs of individuals (general population, or cancer survivors) on the causes of cancer. They reveal a huge discrepancy between scientifically proven factors and spontaneous opinions, that consider "stress" as the major cause of cancer. This is understandable in terms of psychological needs, and must be taken into account in cancer information campaigns.

The need for evolutionary theory in cancer research

Sir Richard Peto is well known for proposing puzzling paradoxes in cancer biology-some more well-known than others. In a 1984 piece, Peto proposed that after decades of molecular biology in cancer research, we are still ignorant of the biology underpinning cancer. Cancer is a product of somatic mutations. How do these mutations arise and what are the mechanisms? As an epidemiologist, Peto asked if we really need to understand mechanisms in order to prevent cancer? Four decades after Peto's proposed ignorance in cancer research, we can simply ask, are we still ignorant? Did the great pursuit to uncover mechanisms of cancer eclipse our understanding of causes and preventions? Or can we get closer to treating and preventing cancer by understanding the underlying mechanisms that make us most vulnerable to this disease?

Chance, ignorance, and the paradoxes of cancer: Richard Peto on developing preventative strategies under uncertainty

During the early 1980s both cancer biology and epidemiological methods were being transformed. In 1984 the leading cancer epidemiologist Richard Peto - who, in 1981, had published the landmark Causes of Cancer with Richard Doll - wrote a short chapter on "The need for ignorance in cancer research", in which the worlds of epidemiology and speculative Darwinian biology met. His reflections on how evolutionary theory related to cancer have become known as "Peto's paradox", whilst his articulation of "black box epidemiology" provided the logic of subsequent practice in the field. We reprint this sparkling and prescient example of biologically-informed epidemiological theorising at its best in this issue of the European Journal of Epidemiology, together with four commentaries that focus on different aspects of its rich content. Here were provide some contextual background to the 1984 chapter, and our own speculations regarding various paradoxes in cancer epidemiology. We suggest that one reason for the relative lack of progress in indentifying novel modifiable causes of cancer over the last 40 years may reflect such exposures being ubiquitous within environments, and discuss the lessons for epidemiology that would follow from this.

Cancers make their own luck: theories of cancer origins

Cancer has been a leading cause of death for decades. This dismal statistic has increased efforts to prevent the disease or to detect it early, when treatment is less invasive, relatively inexpensive and more likely to cure. But precisely how tissues are transformed continues to provoke controversy and debate, hindering cancer prevention and early intervention strategies. Various theories of cancer origins have emerged, including the suggestion that it is 'bad luck': the inevitable consequence of random mutations in proliferating stem cells. In this Review, we discuss the principal theories of cancer origins and the relative importance of the factors that underpin them. The body of available evidence suggests that developing and ageing tissues 'walk a tightrope', retaining adequate levels of cell plasticity to generate and maintain tissues while avoiding overstepping into transformation. Rather than viewing cancer as 'bad luck', understanding the complex choreography of cell intrinsic and extrinsic factors that characterize transformation holds promise to discover effective new ways to prevent, detect and stop cancer before it becomes incurable.

The estimated burden of ultra-processed foods on cardiovascular disease outcomes in Brazil: A modeling study

Introduction

Ultra-processed foods (UPF) have been associated with an increased risk of cardiovascular diseases (CVD). This study aimed to estimate CVD premature deaths, incident cases, and disability adjusted life-years (DALYs) attributable to the consumption of UPF in Brazilian adults in 2019.

Methods

A validated a comparative risk assessment model was adapted to estimate the burden of major CVD outcomes (coronary heart disease and stroke) attributable to the consumption of UPF in Brazilian adults aged 30 to 69 years. The model inputs included nationally representative data of the UPF contribution to the total energy of the diet, national official demographic records, CVD outcomes (incidence, deaths and DALYs) from the Global Burden of Disease study for 2019, and relative risks from meta-analysis studies.

Results

We estimated that approximately 19,200 premature deaths (95% uncertainty intervals - UI, 7,097 to 32,353), 74,900 new cases (95% UI, 25,983 to 128,725), and 883,000 DALYs/year (95% UI, 324,279 to 1,492,593) from CVD were attributable to the consumption of UPF in Brazil, corresponding to about 22% of the premature deaths from CVD and to 33% of the total premature all-cause deaths attributable to UPF intake among Brazilian adults. Reducing UPF consumption by 10% in the adult population would avert approximately 11% of the premature CVD deaths, equivalent to 2,100 deaths/year (95% UI, 697 to 4,511). A 20% reduction in UPF intake would avert approximately 21% of the premature CVD deaths or 4,100 deaths (95% UI, 1,413 to 8,047), and a 50% reduction in UPF intake would avert about 52% of the premature CVD deaths, corresponding to 9,900 deaths/year (95% UI, 3,682 to 17,820). If UPF consumption among adults was reduced to that of the first quintile of UPF intake in the baseline scenario, approximately 81% of the premature CVD deaths would be averted, corresponding to some 15,600 deaths/year (95% UI, 5,229 to 27,519).

Conclusion

Our study estimated a high burden of premature CVD outcomes attributable to the consumption of UPF in Brazil. Our findings support food policies aimed at reducing the consumption of UPF, such as fiscal and regulatory policies, which are imperative to prevent CVD in Brazil.

One person's meat is another's poison: representations of the meat-health nexus in UK news media

Mainstream media play a central role in shaping the ways diet and nutrition are discussed in the public sphere, yet few studies have explored its depictions of the meat-health nexus. Focusing on eight of the most popular news online sites consumed by lower-income groups in the UK—the demographic most likely to eat meat, according to a survey conducted for this study—we carried out content analysis of 128 articles. We found, first, a multiplicity of pro- and anti-meat narratives across all news outlets; second, that the dominant recommendation, found in 40% of our sample, was to eat less or no red meat; and third, that a balanced or neutral sentiment was present in over half of our sample, with a ratio of 3:2 (anti-versus pro-meat) in remaining articles. We found that the editorial leaning of a news outlet was not closely correlated with its overall sentiment towards meat consumption; all were neutral or slightly anti-meat, with the exception of LAD Bible, the only clearly pro-meat outlet. Qualitative analysis uncovered three key themes: the risk of red meat on colorectal cancer, uncertainty around plant-based options, and individual dietary choice. We use case studies guided by these themes to highlight some of the shortcomings of health communication and provide recommendations, with a focus on improved dialogue between journalists and researchers.

Identifying Novel Causes of Cancers to Enhance Cancer Prevention: New Strategies Are Needed

The burden of cancer from a clinical, societal, and economic viewpoint continues to increase in all parts of the world, along with much debate regarding how to confront this. Projected increases in cancer indicate a 50% increase in the number of cases over the next 2 decades, with the greatest proportional increase in low- and medium-income settings. In contrast to the historic high cancer burden due to viral and bacterial infections in these regions, future increases are expected to be due to cancers linked to westernization including breast, colorectum, lung, and prostate cancer. Identifying the reasons underlying these increases will be paramount to informing prevention efforts. Evidence from epidemiological and laboratory studies conducted in high-income countries over the last 70 years has led to the conclusion that approximately 40% of the cancer burden is explained by known risk factors-the 2 most important being tobacco and obesity in that order-raising the question of what is driving the rest of the cancer burden. International cancer statistics continue to show that approximately 80% of the cancer burden in high-income countries could be preventable in principle, implying that there are important environmental or lifestyle risk factors for cancer that have not yet been discovered. Emerging genomic evidence from population and experimental studies points to an important role for nonmutagenic promoters in driving cancer incidence rates. New research strategies and infrastructures that combine population-based and laboratory research at a global level are required to break this deadlock.

Prospective evaluation of a breast-cancer risk model integrating classical risk factors and polygenic risk in 15 cohorts from six countries

BACKGROUND

Rigorous evaluation of the calibration and discrimination of breast-cancer risk-prediction models in prospective cohorts is critical for applications under clinical guidelines. We comprehensively evaluated an integrated model incorporating classical risk factors and a 313-variant polygenic risk score (PRS) to predict breast-cancer risk.

METHODS

Fifteen prospective cohorts from six countries with 239 340 women (7646 incident breast-cancer cases) of European ancestry aged 19-75 years were included. Calibration of 5-year risk was assessed by comparing expected and observed proportions of cases overall and within risk categories. Risk stratification for women of European ancestry aged 50-70 years in those countries was evaluated by the proportion of women and future cases crossing clinically relevant risk thresholds.

RESULTS

Among women <50 years old, the median (range) expected-to-observed ratio for the integrated model across 15 cohorts was 0.9 (0.7-1.0) overall and 0.9 (0.7-1.4) at the highest-risk decile; among women ≥50 years old, these were 1.0 (0.7-1.3) and 1.2 (0.7-1.6), respectively. The proportion of women identified above a 3% 5-year risk threshold (used for recommending risk-reducing medications in the USA) ranged from 7.0% in Germany (∼841 000 of 12 million) to 17.7% in the USA (∼5.3 of 30 million). At this threshold, 14.7% of US women were reclassified by adding the PRS to classical risk factors, with identification of 12.2% of additional future cases.

CONCLUSION

Integrating a 313-variant PRS with classical risk factors can improve the identification of European-ancestry women at elevated risk who could benefit from targeted risk-reducing strategies under current clinical guidelines.

Random cancers as supported by registry data

There has been considerable interest in recent years in quantifying the rate of unavoidable or so-called random cancers, as opposed to cancers linked to environmental, genetic or other factors. We propose a data-based approach to estimate an upper limit to this probability, based on an analysis of multiple registry data. The argument is that the cumulative hazards for random cancers cannot exceed the minimum reliable cumulative hazard observed across the registries. We propose a Monte Carlo method to identify this upper limit and apply the method to data on nine different cancers recorded by 423 registries. We compare our values with estimates obtained from a random mutations argument.

Post-Modern Epidemiology: When Methods Meet Matter

In the last third of the 20th century, etiological epidemiology within academia in high-income countries shifted its primary concern from attempting to tackle the apparent epidemic of noncommunicable diseases to an increasing focus on developing statistical and causal inference methodologies. This move was mutually constitutive with the failure of applied epidemiology to make major progress, with many of the advances in understanding the causes of noncommunicable diseases coming from outside the discipline, while ironically revealing the infectious origins of several major conditions. Conversely, there were many examples of epidemiologic studies promoting ineffective interventions and little evident attempt to account for such failure. Major advances in concrete understanding of disease etiology have been driven by a willingness to learn about and incorporate into epidemiology developments in biology and cognate data science disciplines. If fundamental epidemiologic principles regarding the rooting of disease risk within populations are retained, recent methodological developments combined with increased biological understanding and data sciences capability should herald a fruitful post-Modern Epidemiology world.

Genetics of biologically based psychological differences

In recent years, substantial effort has gone into disentangling the genetic contribution to individual differences in behaviour (such as personality and temperament traits). Heritability estimates from twin and family studies, and more recently using whole genome approaches, suggest a substantial genetic component to these traits. However, efforts to identify the genes that influence these traits have had relatively little success. Here, we review current work investigating the heritability of individual differences in behavioural traits and provide an overview of the results from genome-wide association analyses of these traits to date. In addition, we discuss the implications of these findings for the potential applications of Mendelian randomization.This article is part of the theme issue 'Diverse perspectives on diversity: multi-disciplinary approaches to taxonomies of individual differences'.

Inequality in genetic cancer risk suggests bad genes rather than bad luck

Heritability is often estimated by decomposing the variance of a trait into genetic and other factors. Interpreting such variance decompositions, however, is not straightforward. In particular, there is an ongoing debate on the importance of genetic factors in cancer development, even though heritability estimates exist. Here we show that heritability estimates contain information on the distribution of absolute risk due to genetic differences. The approach relies on the assumptions underlying the conventional heritability of liability model. We also suggest a model unrelated to heritability estimates. By applying these strategies, we describe the distribution of absolute genetic risk for 15 common cancers. We highlight the considerable inequality in genetic risk of cancer using different metrics, e.g., the Gini Index and quantile ratios which are frequently used in economics. For all these cancers, the estimated inequality in genetic risk is larger than the inequality in income in the USA.

Psychological distress in relation to site specific cancer mortality: pooling of unpublished data from 16 prospective cohort studies

OBJECTIVE

 To examine the role of psychological distress (anxiety and depression) as a potential predictor of site specific cancer mortality.

DESIGN

 Pooling of individual participant data from 16 prospective cohort studies initiated 1994-2008.

SETTING

 Nationally representative samples drawn from the health survey for England (13 studies) and the Scottish health survey (three studies).

PARTICIPANTS

 163 363 men and women aged 16 or older at study induction, who were initially free of a cancer diagnosis, provided self reported psychological distress scores (based on the general health questionnaire, GHQ-12) and consented to health record linkage.

MAIN OUTCOME MEASURE

 Vital status records used to ascertain death from 16 site specific malignancies; the three Scottish studies also had information on cancer registration (incidence).

RESULTS

 The studies collectively contributed an average of 9.5 years of mortality surveillance during which there were 16 267 deaths (4353 from cancer). After adjustment for age, sex, education, socioeconomic status, body mass index (BMI), and smoking and alcohol intake, and with reverse causality (by left censoring) and missing data (by imputation) taken into account, relative to people in the least distressed group (GHQ-12 score 0-6), death rates in the most distressed group (score 7-12) were consistently raised for cancer of all sites combined (multivariable adjusted hazard ratio 1.32, 95% confidence interval 1.18 to 1.48) and cancers not related to smoking (1.45, 1.23 to 1.71), as well as carcinoma of the colorectum (1.84, 1.21 to 2.78), prostate (2.42, 1.29 to 4.54), pancreas (2.76, 1.47 to 5.19), oesophagus (2.59, 1.34 to 5.00), and for leukaemia (3.86, 1.42 to 10.5). Stepwise associations across the full range of distress scores were observed for colorectal and prostate cancer.

CONCLUSION

 This study contributes to the growing evidence that psychological distress might have some predictive capacity for selected cancer presentations, in addition to other somatic diseases.