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.

Results

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.

Risk factors

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.

Future work

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.

Further information

Charlotte Sturley, who carried out this study as part of her PhD research, presented the work at the 19^th International Medical Geography Symposium 2022, which is being held at the Royal College of Surgeons of Edinburgh from 19^th-24^th June

Her presentation is available here: (PDF) Contrasting socio-economic influences on colorectal cancer incidence and survival (researchgate.net)

Read the full paper

How does our social environment influence our chances of getting cancer? New research using Census data by Professor Robert Hiatt and colleagues shows there is a link between socio-economic status and cancer incidence, but also throws up some unexpected findings. In the first of a series of three blogs on socio-economic links to cancer, he discusses his work.

It’s well known that specific health outcomes are affected by socio-economic status – for instance the Whitehall IIlongitudinal study of civil servants clearly demonstrated this relationship as did subsequent Marmot reviews including the 2010 Marmot review of health inequalities. Recent research using the ONS Longitudinal Study has shown us in more detail the connections between socio-economic status and cancer survival, but we also wanted to look at how our background might be connected with the onset or incidence of different cancers as well as with their outcomes.

We now know that people from more deprived backgrounds have lower survival rates when they have cancer, although the causes of this are multi-faceted. We know that those with higher social status have access to critical knowledge, money, power, prestige, and social connections, which plays out to their benefit for cancer as well as any number of other health outcomes. There is a complex interplay between these fundamental aspects of their lives and their incomes, occupations, education, income, education, culture migration status and sexual orientation.  And that in turn affects the material resources they have, their food security, their internet access, the type of healthcare they can access, their exposure to discrimination and stigma, and the support networks on which they can rely.

Those with lower socio-economic status on the other hand are missing out on many of the fundamental underpinnings leading to good health and in addition are more likely to be exposed to things like environmental toxins and climate change. In some cases, they may also be more likely to adopt unhealthy behaviours, such as smoking or a lack of physical activity. So, when it comes to the social determinants of cancer, the picture is multi-level, complex and a challenge to understand.

The ONS-LS can’t tell us everything about the possible links between social determinants and cancer, but it does allow us to look at different types of cancer diagnoses by occupational status, level of education and household characteristics, as well as by the type of area in which a person lives.

We were able to take data on almost 140,000 individuals who were alive in 1971, based on a one per cent random sample from the census, and look at the types of cancer diagnoses among them taking into account some of these social factors.

Two major questions

We asked two major questions: How does socio-economic position, measured both by area of residence and by individual characteristics, relate to cancer incidence and mortality? And how do social factors such as education, social class, occupation, home location and prior health status contribute to the relationship between socio-economic position and cancer outcomes?

We looked at all the major types of cancer – the biggest are lung cancer, breast cancer, colorectal cancer and prostate cancer. Overall incidence (onset of new cancers) tended to be higher among those with lower socio-economic status.  But of course, behavioural factors such as smoking could be instrumental in that relationship and there is no data on smoking status in the ONS LS. So we looked again after eliminating those cancers with links to tobacco – and still found the same effect.

When we looked at individual cancers rather than overall rates, a rather different picture emerged. For those from lower social groups, there was a higher risk of being diagnosed with lung cancer, cervical cancer and stomach cancer. But those groups actually had a lower likelihood of contracting breast cancer, prostate cancer or melanoma. The relationship went in opposite directions depending on the cancer site. There were some also major cancers including colorectal cancer for which there wasn’t a clear social pattern.

We examined this relationship both through the lens of respondents’ income and education, and by the area in which they lived, and we came up with similar findings.

The implications

So what are the implications? At this stage, the full picture isn’t clear. We can say that overall, those from poorer backgrounds are more at risk of contracting cancer. And we know the reasons for that are complex. Lung cancer is certainly linked to smoking, so that must be a factor – and these social groups may also have higher exposure to the human papillomavirus (HPV), the major cause of cervical cancer, or to H. pylori bacteria, which live in the digestive tract and are linked with gastric cancers.

We can also say that those from wealthier backgrounds are more at risk from certain types of cancer. We may speculate that in some cases there will be behavioural and social factors at work – for instance, women who have children later in life or remain childless are at greater risk of breast cancer. These may tend to be the more highly-educated women who want to pursue their careers. But at present we don’t have any good theories on why prostate cancer might be more common among men from higher socio-economic groups. So our research raises questions as well as answers.

Our measures of individual socio-economic position are based on crude categories of income, education and occupational status, but may not give us a full picture. And we haven’t yet interpreted our findings in the context of the societal changes which has taken place since 1971.

There is much more work to be done in this area. We plan to publish three papers; one on socioeconomic status and cancer incidence, a second on socioeconomic status and mortality and a third comparing incidence with mortality. There will be detailed studies of individual cancers, too – so the ONS-LS will continue to prove a rich resource for cancer researchers in this and other areas.

Robert Hiatt’s presentation on Social Gradients in Cancer Incidence (and Mortality): the ONS Longitudinal Study was given on May 23, 2022 at University College London, and was based on forthcoming research with Nicola Shelton, Wei Xun and Eduardo Santiago-Rodriguez.