We know cancer incidence is linked to socio-economic status, but that this differs according to types of cancer. In the second of three blogs on research using the ONS-LS to explore cancer and social status, Charlotte Sturley has examined diagnoses of bowel cancer, and found some clear evidence of a social effect.
Bowel cancer – also known as colorectal cancer – is the fourth most common cancer in the UK. Over 42,000 people are diagnosed with it in the UK each year so it is a major public health problem.
Cancer incidence varies between different groups of people, and differences have been found based on gender, age, ethnicity and where people live.
In England, for most cancer types, incidence is higher in the most deprived areas compared with the least deprived. The deprivation gap is largest for lung cancer, reflecting the fact that more deprived groups are more likely to smoke. Conversely some cancer types, such as breast cancer in females and prostate cancer in males, are more common in the least deprived areas.
The association between colorectal cancer and deprivation is less clear, and findings from previous studies have been inconsistent. In the 1980s, affluence was associated with an increased risk of colon and rectal cancer in Europe. But more recently, evidence has emerged of links between this type of cancer and living in a deprived area.
Understanding the causes
Given this apparent shift in the relationship between socio-economic deprivation and colorectal cancer, it is important for researchers to monitor recent data to see if the patterns are changing. We also need to understand the extent to which inequalities are associated with both individual and area-level factors to better target their underlying causes.
Most research on inequalities in cancer incidence has focussed on indicators of deprivation at area level, largely because cancer registries do not collect data on indicators of socio-economic position, such as the patient’s level of education or occupation.
Using Census Data to dig deeper
The Office for National Statistics Longitudinal Study (ONS LS) offers the opportunity to investigate variations in cancer incidence using information gathered in the census on individuals’ socioeconomic positions. My study used measures of educational attainment, occupational social class and housing tenure, along with an area-based measure of deprivation called the Townsend deprivation score.
My sample were LS members who were present at the 2001 Census and were aged 50 years or over, as incidence of colorectal cancer is very low among people aged under 50.
Among the study sample of 178,116 individuals present at the 2001 census, there were 4,418 cases of colorectal cancer recorded by the end of 2015. Because the ONS LS links census responses to cancer diagnoses, we could measure the average length of time between the 2001 census and the diagnosis.
The study found evidence of socio-economic inequalities in colorectal cancer incidence and that these differences varied by indicator of socio-economic position. LS members with a degree were less likely to have a colorectal cancer diagnoses compared to those without a degree, after accounting for differences by age, sex, ethnicity and area deprivation. A statistically significant association was also observed between housing tenure and colorectal cancer incidence, but only for those in social rented housing, who were at an increased risk of colorectal cancer compared to owner-occupiers.
Those employed in manual occupations were more likely to have a colorectal cancer diagnosis, compared to those in non-manual occupations – however this association was not statistically significant when adjusted for other variables. There was no statistically significant difference in colorectal cancer risk among study members in private rented accommodation compared to those in owner-occupied housing. No significant variation in colorectal cancer incidence was found by the level of area deprivation.
So, we can say individual measures of socio-economic position based on educational attainment and housing tenure are associated with colorectal cancer. My finding that there is not a link with area-level deprivation differs from other recent research which reported an emerging association between this type of cancer and deprivation, measured at the area-level. But these other studies used a different measure of deprivation which means comparisons are more difficult. The longitudinal nature of the LS data and the long-follow up period enabled time-to-event analysis to be employed in my study, whereas previous studies have tended to be more of a snapshot.
Not all individuals living in deprived areas will experience the same level of deprivation, and that could explain why I did not find area effects even though I did find individual ones.
One explanation for an association between colorectal incidence and socio-economic position could be different levels of exposure to risk factors such as poor diet or smoking. There is strong evidence to link socio-economic disadvantage with such behaviours.
My study highlights the complexity of the relationship between socio-economic circumstances and health outcomes and the need to investigate socio-economic inequalities by a range of different indicators in order to implement targeted policy interventions to reduce cancer incidence.
An interesting next step using the LS would be to investigate if and how change in individual socio-economic position and area deprivation over a person’s lifetime might influence their risk of having a colorectal cancer diagnosis. Linking the LS to data from the bowel cancer screening programme to investigate the impact of screening on colorectal cancer incidence and socioeconomic inequalities would also provide valuable insight.
Charlotte Sturley, who carried out this study as part of her PhD research, presented the work at the 19th International Medical Geography Symposium 2022, which is being held at the Royal College of Surgeons of Edinburgh from 19th-24th June
Her presentation is available here: (PDF) Contrasting socio-economic influences on colorectal cancer incidence and survival (researchgate.net)