Inequality in survival of people with head and neck cancer

Ingarfield, Kate (2021) Inequality in survival of people with head and neck cancer. PhD thesis, University of Glasgow.

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Abstract

Background:

Socioeconomic inequalities in the relationship between lower socioeconomic status and circumstances with poorer survival of people with head and neck cancer have previously been described. However, the extent and nature of socioeconomic inequality in survival of people with head and neck cancer is poorly understood and explanations for these inequalities are yet to be thoroughly investigated. In particular, the underlying determinants of inequality in survival of people with head and neck cancer is yet to be explored by comparing factors that might be more modifiable with factors that might be more difficult to modify or control. In addition, no study exists from the United Kingdom (UK) that has explored socioeconomic inequality in survival of people with head and neck cancer using individual measurements of socioeconomic status, such as household income or education level, and few studies have investigated the long-term impact of inequality on survival of people with head and neck cancer beyond five-years. Finally, no studies have examined inequality in survival of people with head and neck cancer by utilising metrics of inequality. Further investigations into socioeconomic inequality in survival of people with head and neck cancer need to be conducted to describe and compare inequality with the aim to explain the underlying drivers of inequality in survival for people with head and neck cancer in the short-term, middle-term, and long-term follow-up.

Aim:

This thesis has the potential to shine a light on the issue of socioeconomic inequality in survival of people with head and neck cancer. This thesis aims to inform the patients, public, clinicians, and policy makers who are involved with head and neck cancer services on the magnitude of socioeconomic inequality in survival of people with head and neck cancer, and what factors can explain these inequalities. A series of epidemiological studies of existing UK cohort studies will be conducted to explore this topic from different angles with the aim to inform policy and practice to further the development and delivery of head and neck cancer services.

The overall aim of this thesis is to: describe the trends in socioeconomic determinants and inequalities in survival from head and neck cancer over calendar time and follow-up time; to understand socioeconomic inequality in survival of people with head and neck cancer; and to explain the underlying determinants and explanations of socioeconomic inequality in survival of people with head and neck cancer. In addition, multiple measurements of survival will be utilised and compared, including overall survival, disease-specific survival, and net survival estimates, as well as measurements of inequality including the slope index of inequality and the relative index of inequality. Finally, both area-based measurements and individual measurements of socioeconomic status will be utilised and compared for their association with inequality in survival of people with head and neck cancer.

Methods:

Four studies were conducted with the aim to explore the magnitude, extent, and underlying determinants of survival and inequality in survival of people with head and neck cancer in the UK.

Chapter 2 provides an overview analysis of socioeconomic determinants in survival by utilising data from the Scottish Cancer Registry of people diagnosed with head and neck cancer between 1986 to 2015. Due to the limitations around the availability of data in cancer registries, the explanations for socioeconomic inequality were not explored in this chapter and therefore, this chapter was an epidemiological analysis of the trends and magnitude of socioeconomic inequalities in survival over time.

Chapter 3 analyses the determinants of survival from head and neck cancer by utilising the Scottish Audit of Head and Neck Cancer (SAHNC), a population-based clinical cohort study of people with head and neck cancer who were diagnosed between 1999 and 2001. Multiple patient, tumour, and treatment factors were examined for their predictive ability with survival, including area-based socioeconomic deprivation. Several methods of measuring survival were compared and contrasted in this chapter, including overall survival, disease-specific survival, and net survival estimates after one year, five years, and 12 years of a diagnosis of head and neck cancer.

Chapter 4 also uses the SAHNC cohort and built upon Chapter 3by exploring the drivers and explanations for the socioeconomic inequality observed after one year, five years, and 12 years of a diagnosis of head and neck cancer. The patient, tumour, and treatment factors were individually examined for their relationship with socioeconomic factors with the aim of determining the underlying causes of socioeconomic inequality in survival of people with head and neck cancer. This chapter also explored these inequalities via different survival metrics–overall survival, disease-specific survival, and net survival estimates.

Chapter 5 investigated the relationship of individual socioeconomic factors and explanations for these relationships using a cohort of people with head and neck cancer that were diagnosed between 2011 and 2014 in a population-based clinical cohort study in England; Head and Neck 5000 (HN5000). This part of the thesis aimed to undertake an in-depth exploration into the nature and extent of the socioeconomic inequality in survival of people with head and neck cancer by considering both area-based and individual dimensions of socioeconomic circumstances. Multiple demographic, health, behavioural, tumour, and treatment factors were considered to help understand the relationship between socioeconomic factors and head and neck cancer survival. This analysis built upon the previous chapters with multiple individual socioeconomic measurements and several additional potential explanatory factors collected as part of a more recent cohort study of people with head and neck cancer, including human papillomavirus (HPV) status.

Results:

As a whole, this thesis demonstrated strong and consistent socioeconomic inequalities in survival of people with head and neck cancer. These inequalities in survival of people with head and neck cancer appeared to become worse over calendar time and also across follow-up period after one year, five years, and ten years of a diagnosis of head and neck cancer (Chapter 2–Scottish Cancer Registry). Chapter 3 found that socioeconomic status was not an independent predictor of survival in a cohort of people with head and neck cancer who were diagnosed in Scotland between the years of 1999 and 2001(SAHNC), while Chapter 4 investigated the underlying factors that may explain the original inequality that was observed in overall survival, disease-specific survival, and net survival estimates(also the SAHNC). Chapter 4 highlighted that in models that were adjusted by various patient, tumour, and treatment factors, none of the factors could individually explain the socioeconomic inequality in survival alone, suggesting that socioeconomic inequality in survival of people with head and neck cancer is complex, with multiple factors having a combined effect, including background mortality in the long-term follow-up (via net survival estimates). The studies that were carried out in Chapter 2 to Chapter 4 only utilised area-based socioeconomic measurements –mainly Carstairs Deprivation Index.

Chapter 5 added to this picture by exploring inequality by using both an area-based (Index of Multiple Deprivation (IMD)Category) and individual measurements of socioeconomic status including highest education level attained, number of years spent in education, annual household income, proportion of income from benefits, and financial concerns of living with or after cancer. Only data from England in the HN5000 cohort could be included in this analysis since it was not possible to pool and standardise the varying measurements of IMD (including Scottish IMD and Welsh IMD) across these countries of the UK. This study determined that inequalities were present for all of the measurements of socioeconomic status, however inequality in highest education level, number of years spent in education, and financial concerns of living with or after cancer were explained (fully attenuated) by other factors such as age and smoking status. Inequality across both annual household income and the proportion of income from benefits partly attenuated following the adjustment of all of the potential explanatory factors, however, even after full adjustment, the relationship with survival of these factors of socioeconomic status could not be fully explained by any of the potential patient, tumour, or treatment factors that were included in this study.

The secondary aim of Chapter 3 was to compare methods of measuring survival via the use of overall survival, disease-specific survival, and net survival estimates. The substantial differences between these survival metrics demonstrated the overestimation of deaths that are specific to head and neck cancer when using overall survival, and the underestimation of disease-specific mortality from using death certificates when people have died only from head and neck cancer. These results suggest that people are dying of other causes that are related to their head and neck cancer but are not as a direct result of their cancer, which ultimately increases with time following diagnosis. Therefore, the use of net survival provides a good compromise to traditional methods to estimate the true burden of head and neck cancer in long-term follow-up studies. As a result, throughout Chapter 2 to Chapter 4, net survival estimates have been provided alongside overall survival and disease-specific survival results to compare and contrast the outcomes of people with head and neck cancer. However, in Chapter 5, it was not possible to utilise net survival estimations since lifetables for this time point had not yet been generated at the time of this analysis.

Discussion and Conclusions:

The thesis studied socioeconomic inequality in survival of people with head and neck cancer in the UK using data from three sources –the Scottish Cancer Registry, the SAHNC cohort study of people with head and neck cancer in Scotland, and the HN5000 cohort study of people with head and neck cancer in England. As a whole, this thesis reported that inequality in survival of people with head and neck cancer is a persistent problem–a problem which seems to be getting worse. Moreover, the main premise of this thesis was to further the understanding of explanatory factors of socioeconomic inequality in survival of people with head and neck cancer. Although socioeconomic inequality in survival utilising an area-based measurement of socioeconomic status was explained by various underlying factors, inequality by annual household income and the proportion of income from benefits only attenuated following the adjustment of all potential explanatory factors for patients in England. Even after full adjustment, inequality in survival by annual household income and the proportion of income from benefits could not be explained by any of the potential underlying factors that were included in this study. Therefore, further investigations considering individual measurements of patients’ income following a diagnosis of cancer should be conducted.

In addition, a number of recommendations related to policy, practice, and further research were drawn. This thesis has provided a comprehensive examination of socioeconomic inequalities in survival of people with head and neck cancer –a relatively underexplored field. The research involved in-depth analyses of multiple datasets and from a number of perspectives. It has shown that inequalities in survival are substantial and are a growing problem, and has endeavoured to explore the explanatory factors. This work provides a platform through which policy and practice development, along with evaluation and research, can be based to reduce inequalities in survival and improve the outcome for people who are diagnosed with head and neck cancer.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Subjects: 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
Supervisor's Name: Conway, Professor David and McMahon, Dr. Alex
Date of Award: 2021
Depositing User: Mrs Marie Cairney
Unique ID: glathesis:2021-82320
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 13 Jul 2021 15:14
Last Modified: 13 Jul 2021 15:36
Thesis DOI: 10.5525/gla.thesis.82320
URI: http://theses.gla.ac.uk/id/eprint/82320
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