Socioeconomic inequalities in lung and upper aero-digestive tract cancer incidence in Scotland

Sharpe, Katharine H. (2018) Socioeconomic inequalities in lung and upper aero-digestive tract cancer incidence in Scotland. PhD thesis, University of Glasgow.

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Socioeconomic inequality in cancer risk and incidence burden has received limited attention compared to genetic and behavioural risk factors. Where they have been studied, the temporal relationship between socioeconomic factors and cancer risk has been under explored due to the mainly cross-sectional nature of most research. Moreover, the inter-relationships of the multiple measures of socioeconomic status and, in particular, area and individual measures and their interaction with risk behaviours have also had limited attention. The overarching aim of this thesis was to investigate socioeconomic inequalities in the risk of lung and upper aero-digestive tract cancers and the relationship between this risk and socioeconomic status, area and individual based measures of socioeconomic circumstances, and behaviours such as smoking, alcohol consumption, diet and exercise. To understand and quantify the relative contribution by age, sex and tumour subtype to the socioeconomic inequalities of all cancer risk, a descriptive epidemiological study of cancer incidence in Scotland (2000-07) was undertaken. Age standardised rates per 100,000 population were calculated by direct standardisation to the European standard. A linear regression model was used to calculate the Slope Index of Inequality (SII) and Relative Index of Inequality (RII) which were employed to rank tumour and subtype contribution to all cancer risk socioeconomic inequalities by age for each sex for lung and upper aero-digestive tract (UADT) cancers separately. There were 216,305 cases excluding nonmelanoma skin cancer (all cancer) comprising 37,274 lung, 8,216 head and neck and 6,534 oesophageal cancers classified into anatomical or morphological subtypes. Socioeconomic circumstances were measured using the Scottish Index of Multiple Deprivation (SIMD). Analyses were partitioned by five-year age group and sex. RII was adapted to rank the contribution of each tumour type to all cancer socioeconomic inequalities and to examine subtype by age and sex simultaneously. The rank was defined as the proportion of all cancer socioeconomic inequality. All cancer socioeconomic inequality was greater for males than females (RII=0.366; female RII=0.279). The combination of lung and UADT socioeconomic inequalities contributed 91% and 81% respectively to all cancer socioeconomic inequality. For both sexes lung and UADT subtypes showed significant socioeconomic inequalities (P<0.001) except oesophageal adenocarcinoma in males (P=0.193); for females, socioeconomic inequality was borderline significant (P=0.048). Although RII rank differed by sex, all lung and larynx subtypes contributed the most to all cancer socioeconomic inequality with RII rank for oral cavity, oesophagus–squamous cell and oropharynx following. For males 40-44 years old, socioeconomic inequalities increased abruptly peaking at 55-59 years. For females, socioeconomic inequalities gradually peaked 10 years later. In both sexes, the socioeconomic inequalities peak age preceded age of peak incidence. This study showed that socioeconomic inequalities in lung and UADT cancers vary greatly by age, tumour subtype and sex; these variations were likely to largely reflect differences between the sexes in risk behaviours which vary by birth cohort and are socioeconomically patterned. Longitudinal data enabled exploration of the temporal relationship between socioeconomic status and cancer incidence. An investigation of several individual and a single area-based measure of socioeconomic circumstances was undertaken in the second study of this thesis. The effect of country of birth, marital status, one area socioeconomic circumstances measure (Carstairs) and five individual socioeconomic variables (economic activity, education, occupational social class, car ownership, household tenure) on the risk associated with lung, UADT and all cancer combined (excluding non-melanoma skin cancer) were explored. A linked dataset using the Scottish Longitudinal Study and Scottish Cancer Registry was created to follow 203,658 cohort members aged 15+ years from 1991-2006. Relative risks (RR) were calculated using Poisson regression models by sex offset for person-years of follow-up. There were 21,832 first primary tumours (including 3,505 lung and 1,206 UADT cancers). Regardless of cancer, economic inactivity (versus activity) was associated with increased risk (male: RR 1.14 95% CI 1.10, 1.18; female: RR 1.06 95% CI 1.02, 1.11). For lung cancer, area deprivation remained significant after full adjustment suggesting that the area deprivation cannot be fully explained by individual variables. Not having a qualification (versus degree) was associated with increased lung cancer risk; likewise for UADT cancer risk (females only). Occupational social class associations were most pronounced and elevated for UADT risk. No car access (versus ownership) was associated with increased risk (excluding all cancer risk for males). Renting accommodation (versus home ownership) was associated with increased lung cancer risk, UADT cancer risk for males only and all cancer risk for females only. Regardless of cancer group, elevated risk was associated with no education and living in deprived areas. This study demonstrated that different and independent socioeconomic variables were inversely associated (greater incidence with lower socioeconomic circumstances) with different cancer risks in both sexes; no one socioeconomic variable had a dominant risk association or captured all aspects of socioeconomic circumstances or the full life-course. The association of multiple socioeconomic variables was likely to reflect the complexity and multifaceted nature of low socioeconomic circumstances as well as the various roles of these dimensions over the life-course. A final study investigated the role of behaviours (smoking, alcohol, diet and exercise) on the association of low socioeconomic circumstances with all cancer risk and lung and upper aero-digestive tract cancers combined (LUADT). The Scottish Cancer Registry and Scottish Health Survey data were linked to create a population study (1995-2011). There were 42,983 adults over 16 years old who were followed for 3,750,611 person-years. There were 2,130 first primary cancers diagnosed including 453 LUADT cancers. Poisson regression models, minimally adjusted by age and sex, were developed to estimate the risk association between five individual socioeconomic variables (economic activity, highest qualification, occupational social class, car ownership and housing tenure), one area-based socioeconomic indicator (SIMD) and all cancer and LUADT cancer. A further socioeconomic indicator was developed to reflect multiple low socioeconomic circumstances. This was defined as the count, at the individual participant level, of socioeconomic variables in the highest risk category. A similar multiple high risk behaviour derived variable, defined as the count of highest risk category for the following variables: current smoking status, units of alcohol consumed in a week, daily fruit and vegetable consumption and exercise sessions per week, was also calculated at the individual participant level. The minimally adjusted Poisson models were successively adjusted for behaviours (smoking, alcohol, diet and exercise) to establish any remaining contribution to cancer risk not explained by behaviour. Multiple low socioeconomic circumstances were very strongly associated with increased risk for both cancer groups. For all cancer risk, the elevated risk was nearly fully attenuated for all categories of multiple low socioeconomic circumstances when adjusted for smoking only. For LUADT cancer and in the minimally adjusted model, the risk increased in a dose-response manner. The risk associated with LUADT cancer for study participants in the highest category of multiple low socioeconomic circumstances was more than three-times greater when compared to their affluent counterparts (RR 3.35 95% CI 2.26, 4.97); this elevated risk remained at 86% compared to those with no socioeconomic disadvantage, even after full adjustment for smoking, alcohol, diet and exercise behaviours. When looking at single socioeconomic status (SES) indicators, only those who rented accommodation from a local authority remained at a 50% increased risk of LUADT cancer even after adjustment for all the behaviours (RR 1.50 95% CI 1.05, 2.16). This study demonstrated that smoking is a major inequality issue and a significant cancer risk which is socially patterned. Further analytical research is required to fully understand the pathways and mechanisms between socioeconomic circumstance and lung and upper aerodigestive cancer risk. This thesis suggests that when monitoring socioeconomic inequalities and cancer risk, it is less effective to focus on all cancer as a group given the mix of diseases resulting from very different aetiological processes, some associated with high SES and others with low SES. It also suggests that both individual and area measures of SES are valid measures and are required to capture the multi-dimensional nature of SES as well as the life-course and intergenerational implications of SES. In addition to this “multi-dimensional” attribute to SES, it is essential to consider multiple low social circumstances occurring simultaneously and therefore compounding vulnerability to cancer risk. Behaviours, particularly smoking and alcohol, explained much of the elevated lung and upper aero-digestive tract cancer risk for individual SES indicators. Clearly, in this context, smoking is a major inequality issue and a significant cancer risk. This thesis provides useful insights for raising the issue of inequalities in cancer, for advocacy and for building policy and interventions to tackle inequalities in cancer incidence. Policies need to focus on more broadly upstream causes. Traditionally, these policies have been focused on downstream behaviours (e.g. public space smoking ban and alcohol minimum pricing), but upstream policies that take on the fundamental political decisions regarding the distribution of income, wealth and power are required at both Westminster and Holyrood and beyond.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: socioeconomic inequalities, poverty, deprivation, cancer incidence, lung, head and neck, oesophageal, tumour, malignancy, neoplasm, social determinant.
Subjects: H Social Sciences > HV Social pathology. Social and public welfare
R Medicine > RA Public aspects of medicine > RA0421 Public health. Hygiene. Preventive Medicine
R Medicine > RC Internal medicine > RC0254 Neoplasms. Tumors. Oncology (including Cancer)
Colleges/Schools: College of Medical Veterinary and Life Sciences > School of Medicine, Dentistry & Nursing
Funder's Name: UNSPECIFIED
Supervisor's Name: Conway, Professor David I. and McMahon, Dr. Alex
Date of Award: 2018
Depositing User: Dr Katharine H Sharpe
Unique ID: glathesis:2018-8887
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 12 Mar 2018 10:56
Last Modified: 12 Mar 2018 11:13

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