The following hypotheses describe the focus of this thesis.
The distribution of the burden of cancer incidence is unequal among SES groups and this varies by SES measure, cancer site and over time and is increasing over time. Different approaches to measuring and presenting
Chapter 2 literature review — Part II: cancer incidence disease burden by SES
149
SES inequalities will be required to summarise inequalities.
Certain individual SES factors have a greater role in determining cancer risk than others (e.g. education). Area-based SES factors play a role, but may be less significant than individual SES factors.
Multiple or compounded low SES factors will confer an increased risk association with cancer incidence.
Risk behaviours associated with SES will explain a proportion of the SES gradients observed for the selected cancer sites incidence.
The temporal relationship between SES exposure and cancer diagnosis requires to be reflected in the timing of SES exposure measurement. These will be tested via the following studies and associated objectives:
Chapter 3 To undertake a detailed analysis of the Scottish Cancer
Registry to investigate socioeconomic inequality by age, sex and tumour subtype/site
To quantify the relative contribution to all cancer socioeconomic inequalities by tumour subtype/site and differences by sex and age in order to assist in providing explanations for socioeconomic inequalities.
To rank tumour and subtype contribution to all cancer socioeconomic inequalities by age for each sex for lung and UADT cancers using complex metrics of inequality (Slope Index of Inequality and Relative Index of Inequality).
Chapter 4 To explore the association of cancer incidence with
demographic, social and five individual socioeconomic variables (economic activity, occupational social class,
Chapter 2 literature review — Part II: cancer incidence disease burden by SES
150
educational attainment level, car ownership and household tenure) variables through novel data linkage between the Scottish Cancer Registry and the Scottish Longitudinal Study. To assess more finely the socioeconomic factors associated
with cancer incidence through: i) Examining the consistency of the relationship between area and individual SES measures associated with cancer incidence; ii) Explaining whether any single measure was particularly associated with cancer incidence; iii) Assessing whether the area measure was fully explained by the individual measures; and iv) Exploring whether there were any synergistic effects between the area deprivation measure and each individual SES variable; and v) assessing temporal relationship between the SES measure and cancer incidence.
Chapter 5 To undertake data linkage between the Scottish Cancer
Registry and the Scottish Health Survey to create cohort study designed to investigate multiple SES and behavioural risk factors and their association with cancer risk (all cancer and lung and upper aero-digestive tract cancers together). To assess whether behaviour risk factors explain the
previously identified socioeconomic magnitude as measured by individual and area SES (and in combination) measures in all cancer (excluding non-melanoma skin cancer) and lung and upper aero-digestive tract incident cancers taken together.
Chapter 6 Through discussion of the thesis findings collectively and in
relation to the existing literature, to contribute to
explanations of inequality in cancer incidence and to the evidence-base for developing public health policies aiming to reduce inequalities in cancer incidence and draw conclusions.
151
3 Socioeconomic inequality in Lung and UADT
cancer incidence in Scotland: quantification of
contribution to all cancer risk and examination
by tumour subtype, five-year age group and sex
3.1
Introduction
In 2012, worldwide, there were 14.1 million new cancer cases. Estimated age – standard rates (world) per 100,000 populations indicate the United States (USA) (males: 347.0, females: 297.4) followed by the EU (males: 311.3, females: 241.3) had the highest incidence rates (Ervik et al 2016). In the UK, a cancer diagnosis is more common than getting married or having a first baby (Knapton S 2017).
Projections for 2030 indicate that these figures will double. Cancer is increasing at rates faster than the increase in global population. It is becoming more common in high-income but also — and most of all — in middle and low-income countries, absolutely and also relative to other diseases (WCRF/AICR 2007). In Scotland, the number of new cases of cancer (excluding non-melanoma skin cancer) is predicted to rise by 33% between 2008-12 and 2023-27, mainly as a result of the population growing older (ISD 2015).
Lung and upper aero-digestive tract (UADT) comprising head and neck (larynx, oral cavity and oropharynx) and oesophageal cancers together are the most common worldwide; 21% of global cases were diagnosed in Europe in 2012 (IARC 2008). These cancers show socioeconomic inequalities with greater incidence among lower socioeconomic groups (Hemminki et al 2003; Anderson et al 2008; Conway et al 2008; Conway et al 2010a). Previous research on oesophageal cancer and socioeconomic status (SES) identified increased risk of squamous cell carcinoma (Morgan et al 2007) in lower socioeconomic groups while
adenocarcinoma showed no clear association (Brewster et al 2000). Others who studied lung cancer histological subtypes found increasing incidence among lower socioeconomic groups for all subtypes, although the association was less
Chapter 3
152
strong for adenocarcinoma in both sexes (Bennett et al 2008). Case-control and population cohort studies have found increased incidence in lower
socioeconomic groups for larynx (Anderson et al 2008), oral cavity (Conway et al 2007; Anderson et al 2008; Conway et al 2008) and oropharynx (Anderson et al 2008) cancers.
Area-based indices of SES are increasingly used worldwide to measure effects of SES on health outcomes (Kogevinas et al 1997a). Based on income, employment, education, housing, health, crime and geographic access data, the Scottish Index of Multiple Deprivation (SIMD) is a small area measure of SES regularly used in Scotland (Leyland et al 2007a). Small area SES indices are more likely to be homogenous with respect to socioeconomic characteristics and more closely describe individual SES (MacIntyre et al 2002; Leyland et al 2007a). Given its area basis, SIMD also provides a surrogate measure of physical environmental SES, another important and recognised deprivation factor associated with health and disease (MacIntyre et al 2002).
Several inequality measures are used to monitor socioeconomic associated health inequalities (Harper et al 2009). The Slope Index of Inequality (SII) and Relative Index of Inequality (RII) capture the effect (direction and magnitude) of the inequality gradient as well as the extent (population deprivation
distribution) of absolute and relative SES inequality (Harper et al 2008).