cancer incidence in plymouth€¦ · 1), which shows the incidence of lung cancer across the five...

Cancer Incidence in Plymouth

South West Cancer Intelligence Service

Isles of Scilly

Isles of Scilly

South West Cancer Intelligence Service Cancer Incidence in Plymouth

Cancer incidence in Plymouth

Date: 8th February 2006

Grosvenor House 149 Whiteladies Road Bristol BS6 2RA Tel: 0117 9706474 General enquiries: [email protected] Website address: www.swpho.nhs.uk

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Contents

Chapter 1 Introduction 1

Chapter 2 What causes cancer? 2

Chapter 3 Cancer in cities 3

Chapter 4 Cancer incidence rates for Plymouth 4

Chapter 5 Types of leukaemia and risk factors 7

Chapter 6 Leukaemia and the Tamar estuary 10

Chapter 7 Conclusions 14

Chapter 8 Confidentiality 15

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Chapter 1: Introduction

There are ongoing concerns among residents of Plymouth that radioactive emissions from the Devonport Naval Dockyard into the river Tamar and surrounding environment may have resulted in a higher incidence of cancer, particularly leukaemia, in the Plymouth area. The purpose of this report is to provide an accurate account of the incidence of cancer in the Plymouth area based on data collected by the South West Cancer Intelligence Service (SWCIS). This is the second report prepared on cancer incidence in the Plymouth area.

The South West Cancer Intelligence Service is an NHS organisation and is one of a network of regional cancer registries that collect data on all new cases of cancer diagnosed within their region. Cancer registry data is used to monitor patterns of cancer, especially over time and across geographical areas. The information we provide to local agencies is used to evaluate their progress in improving health and cutting inequalities. The data may also point towards possible public health problems and highlight areas for action. Cancer registries support NHS cancer services in the planning and provision of care for their patients. Clinical audits are conducted to look at how cancer patients are treated and whether treatments have been successful for different types of cancer. We also contribute data to nationally recognised research organisations for their research into the causes of cancer, and the best ways of treating it.

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Chapter 2: What causes cancer?

In this country, around 1 in 3 people will develop cancer at some point in their lives. There are over 200 different types of cancer that occur in different parts of the body. They have many different causes, different symptoms and require different types of treatment. The risk of developing cancer increases with age. Cancer incidence rates rise sharply among people over 45 years of age. Cancers develop because of a complex interaction between our genes, our living environment, lifestyles and chance. The most significant and well-understood risk factor associated with cancer is smoking - around one third of all cancer deaths are attributable to smoking. Other risk factors include a high-fat diet, alcohol abuse, exposure to UV radiation from the sun, and a family history of cancer. In a very few cases, there is a proven link between environmental contamination and cancer. Examples include cases of mesothelioma (a form of lung cancer) among people who have worked in close contact with asbestos, and cases of thyroid cancer in the vicinity of Chernobyl nuclear plant subsequent to the accident in 1986.

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Chapter 3: Cancer in Cities

It is well known that cancer incidence tends to be higher in cities than in rural areas. This is thought to be because the higher levels of socio-economic deprivation found in cities are associated with higher rates of smoking, leading to a high incidence of smoking-related cancers e.g. lung, oesophagus and oral cancers. If the South West Region is divided into five groups depending on the level of socio-economic deprivation, the more affluent groups have a lower incidence of cancer. This is illustrated by the graph below (figure 1), which shows the incidence of lung cancer across the five socio-economic groups.

*based on IMD 2000 indices of deprivation, income domain, national quintiles

Less deprived More deprived Socio-economic group*

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Figure 1. Age Standardised Incidence Rates for Lung Cancer in the South West region 1992-2001.

In many areas of Plymouth, the second biggest city in the region, there are high levels of socio-economic deprivation. Using the same five socio-economic groupings around 40% of wards in Plymouth fall into the most deprived group. The table below (figure 2) shows the percentage of each area falling into the most deprived group for Plymouth, compared to the South West Region, Devon and Cornwall, and Bristol.

Figure 2. Percentage of wards falling into each socio-economic group (based on IMD2000 indices of deprivation, national quintiles of income domain).

Socio-

economic group

SW region Devon & Cornwall

Plymouth Bristol

1 9.8 14.7 40.0 32.4 2 24.1 33.9 25.0 29.4 3 27.1 33.4 30.0 17.6 4 24.3 14.7 5.0 11.8 5 14.6 3.2 0.0 8.8

Plymouth and Bristol have the most deprived inner-city communities in the South West. It is expected that the incidence of smoking-related cancers will be high in these cities.

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Chapter 4: Cancer Incidence Rates for Plymouth

The following graphs (figures 3-18) show age standardised incidence rates for cancer in Plymouth compared to the South West Region as a whole over a 10-year period from 1994 to 2003. Cancer is predominantly a disease of elderly people so populations with a higher proportion of elderly people will have higher rates of cancer. Age standardisation accounts for differences in the age structure of populations so that the cancer incidence rates are directly comparable. Comparisons are also shown with Bristol in order to show cancer incidence in another urban area. The error bars on the graph show 95% confidence intervals, which are used to determine whether the incidence rates are significantly different from each other (see chapter 6 for an explanation of confidence intervals). Where the confidence intervals overlap, the rates are not significantly different.

The rate for Plymouth is significantly higher The rate for Plymouth is significantly lowerthan the South West Region than the South West Region

The rate for Plymouth is significantly higher The rate for Plymouth is significantly higherthan the South West Region than the South West Region

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Fig. 3 All cancers

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Fig. 6 Mesothelioma

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The rate for Plymouth is significantly lower The rate for Plymouth is significantly higherthan the South West Region than the South West Region

There is no significant difference between The rate for Plymouth is significantly lowerPlymouth and the South West than the South West Region

There is no significant difference between There is no significant difference betweenPlymouth and the South West Plymouth and the South West


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Fig. 7 Colorectal cancer

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Fig. 12 Brain cancer

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Fig. 14 Malignant melanoma

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Fig. 11 Bladder cancer

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# Includes multiple myeloma and malignant There is no significant difference betweenimmunoproliferative disorders. Plymouth and the South West

There is no significant difference betweenPlymouth and the South West

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Fig. 15 Leukaemia (all types)

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Fig. 16 Lymphoma (all types)

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Fig. 17 Other haematological cancers #

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Fig. 18 Children aged 0-14

As expected, Plymouth has a higher cancer incidence than the South West Region for cancers which are associated with smoking such as lung and upper-gastrointestinal cancers. Plymouth also has a high incidence of mesothelioma which is a cancer of the lining of the lungs caused by exposure to asbestos. In the 1960s and 1970s, many employees of dockyards and other construction industries were exposed to asbestos in their working environment. Plymouth does not have an unusually high incidence of cancers that have been associated with exposure to radiation, such as leukaemia and thyroid cancer. The incidence of leukaemia in Plymouth (9.9 per 100,000) is in fact slightly lower (though not significantly) than for the South West Region as a whole (10.5 per 100,000).

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Chapter 5: Types of Leukaemia and Risk Factors

5.1 Types of Leukaemia

Leukaemia is not one disease, but a group of related diseases characterised by the proliferation of abnormal white blood cells. There are many different types of leukaemia classified by cell type (e.g. lymphocytic or myeloid), and how fast the disease progresses (chronic or acute). The four most common types of leukaemia are chronic lymphocytic, acute lymphocytic, chronic myeloid and acute myeloid. The table below (figure 19) shows the percentage of leukaemia cases by type in the South West Region between 1992 and 2001

Figure 19. Types of leukaemia in the South West 1992-2001

Type of leukaemia % of leukaemia cases

that were of this type Acute Lymphocytic 9.1 Chronic Lymphocytic 36.5 Acute Myeloid 25.0 Chronic Myeloid 11.7 Other types 17.7 All leukaemia 100

The types of leukaemia typically affecting children are not the same as the types that typically affect adults. The incidence of acute lymphocytic leukaemia is at its highest in very young children whereas chronic lymphocytic leukaemia has a peak in the elderly. The graphs on p.8 (figures 20 and 21) show the relationship between age and the incidence of leukaemia in the South West Region 1992-2001.

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Age band

Figure 20. Relationship between age and the incidence of acute lymphocytic leukaemia

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Figure 21. Relationship between age and the incidence of chronic lymphocytic leukaemia

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5.2 Risk factors for leukaemia

Our knowledge and understanding of the causes of leukaemia have not yet progressed to the point where we can say for certain what caused the cancer in any one individual. A little is known about risk factors that are associated with leukaemia and that these risk factors are different for the different types of leukaemia.

It is known that exposure to high levels of ionising radiation is a risk factor for acute leukaemia. For example, people who have had radiotherapy treatment for another cancer have an elevated risk of developing acute leukaemia. This does not mean that everyone who has had radiotherapy treatment will develop acute leukaemia or that every single case of acute leukaemia has been caused by exposure to

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ionising radiation. Other risk factors associated with acute leukaemia are smoking, certain genetic conditions, some pre-existing blood disorders and exposure to benzene.

The most common type of leukaemia is chronic lymphocytic leukaemia (CLL). Over one third of leukaemias in the South West are of this type. The most significant risk factors associated with CLL are age and gender as it predominantly occurs in elderly men. CLL has no known association with radiation and there is no conclusive evidence to link CLL with any single environmental risk factor.

Radiation is a known risk factor for chronic myeloid leukaemia, but it is thought that the levels of radiation need to be very high in order for an effect to be seen e.g. in atomic bomb survivors or patients who have had radiotherapy treatment for another cancer.

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Chapter 6: Leukaemia and the Tamar Estuary

The incidence of leukaemia in Plymouth is not significantly higher than in the South West Region as a whole. However, residents have expressed concerns over the incidence of leukaemia in particular localities that lie close to the Tamar estuary. To explore this we can use electoral wards as our geographical units. Nationally, the average population of an electoral ward is around 5000 residents. Due to confidentiality restrictions (see chapter 8), it is not possible to provide exact figures for leukaemia incidence at ward level as the number of patients is too small. The maps on pages 12-13 (figures 22 and 23) have been created in order to show patterns of leukaemia incidence across the electoral wards of Plymouth, North East Cornwall and South West Devon, while preserving confidentiality. The maps show electoral wards in Plymouth, West Devon, and North East Cornwall, and are colour-coded to indicate whether the standardised incidence ratio for leukaemia is significantly high, significantly low or not significant. Maps are shown for all types of leukaemia together for the 10 year period 1994-2003, and for leukaemia excluding the chronic lymphocytic type which has no known association with radiation exposure. The standardised incidence ratio (SIR) is a ratio of the number of observed cases in a defined population over a defined time period to the number that would be expected in that population. In this case, the number of expected leukaemias in each ward has been calculated from the average incidence rate over the South West Region. The number of observed cases in each ward has been derived from the SWCIS cancer registry. The SIR is usually expressed as a percentage of observed/expected cases. For example, if the expected number of cases is 1 but the number actually observed is 2, the SIR would be 200%. The calculation to find the expected number of cases in a population usually produces numbers that are not whole numbers. For example the number of expected cases could be 0.3 or 4.2. Obviously, people occur in whole units and the minimum number of cases that can ever be found is 1. The SIR can sometimes look very high but this high number does not necessarily carry any real meaning. For example, if the expected number of cases is 0.3 over 10 years, but actually one case occurs in a 10 year period, the SIR is in excess of 300%. In fact this one case may be the only case over a 30 year period but has happened to occur in the 10 years that we are looking at. It would not be appropriate to draw conclusions that the incidence of cancer in that area is three times as high as expected. A measure is needed that indicates the real meaning of an SIR that appears to be very high. One measure that is commonly used is called

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the 95% confidence interval. If the incidence of a cancer in a population was repeatedly measured over time, you would get a range of values as cancer incidence is never exactly the same from year to year. Some values may be very low and some may be very high but typically, a lot of the values will lie within a small range. The range in which 95% of the values lie is called the 95% confidence interval. When looking at confidence intervals for SIRs, we are interested in whether the lower confidence limit is greater or less than 100%. Remember that an SIR of 100% means that the observed number of cases is exactly the same as the expected number. If we had an SIR of 150% and the confidence interval was 70% to 230%, our range of possible values includes the possibility that the SIR is 100%. If we had an SIR of 150% and the confidence interval was 120-180, the range of possible values does not include 100%. In this case, the SIR is said to be statistically significantly high. Conversely, if the SIR was 60% and the confidence interval was 40-80, the SIR is said to be statistically significantly low.

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Figure 22. Leukaemias, all types together, 1994-2003 (10 year period) North and East Cornwall PCT, Plymouth PCT, South Hams and West Devon PCT Standard registration ratio (compared to SW region), data grouped for 1994 - 2003 Purple dot indicates Devonport Naval Dockyard

Standardised registration ratio (SRR) is:-

Significantly high (The observed number of leukaemia cases between 1994 and 2003 was much higher than expected)

Not significant (The observed number of leukaemia cases between 1994 and 2003 was very close to the number expected)

Significantly low (The observed number of leukaemia cases between 1994 and 2003 was much lower than expected)

0 Plymouth miles

2010

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Figure 23. Leukaemias, excluding CLL, 1994-2003 (10 year period) North and East Cornwall PCT, Plymouth PCT, South Hams and West Devon PCT Standard registration ratio (compared to SW region), data grouped for 1994 – 2003 Purple dot indicates Devonport Naval Dockyard

Standardised registration ratio (SRR) is:-

Significantly high (The observed number of leukaemia cases between 1994 and 2003 was much higher than expected)

Not significant (The observed number of leukaemia cases between 1994 and 2003 was very close to the number expected)

Significantly low (The observed number of leukaemia cases between 1993 and 2003 was much lower than expected)

0 Plymouthmiles

2010

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Chapter 7: Conclusions

Overall, Plymouth did have a higher incidence of cancer than the rest of the South West region for the 10 year period of 1994-2003. This is driven by the higher incidence of some types of cancer e.g. lung cancer and upper gastro-intestinal known to be related to rates of deprivation and smoking. The higher overall rate of cancer is therefore likely to be a result of high smoking prevalence in the city. The same effect is seen in other cities such as Bristol that have high levels of inner city deprivation. The incidence rates of cancers that have some known association with radiation exposure such as leukaemia and thyroid cancer are not unusually high in Plymouth and are in fact slightly below the average for the South West region though the difference is not statistically significant. There is no evidence of a significantly raised incidence rate of leukaemia in the wards near to the Devonport dockyard or in wards that lie close to the Tamar estuary. A few electoral wards in the area of Devon and Cornwall around Plymouth do have a raised incidence of leukaemia. It is to be expected that by chance a small number of wards will show higher than average rates and some lower than average rates. These figures alone do not tell us anything about possible causes of leukaemia. At present our knowledge and understanding of the precise causes of leukaemia are very limited. Organisations such as The Leukaemia Research Fund (www.lrf.org.uk), and the Institute of Cancer Research (www.icr.ac.uk/leukaem/index.htm) continue to fund scientific research that will hopefully provide more of the answers in the future. SWCIS regularly provides data to support ethically approved medical research.

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Chapter 8: Confidentiality

In order to maintain the duty of confidentiality between patients and the medical profession, cancer registries work under very strict rules about what data they can release and to whom they release it. The reports that we publish must not give any details that could be used to identify an individual. Cancer registries have developed a data release policy that has been approved by PIAG (the Patient Information Advisory Group). The PIAG committee consists of medical professionals as well as lay representatives and advises on all aspects of the use of medical information. The duty of PIAG is to ensure that patient’s rights are protected under the terms of the Data Protection Act and the Health and Social Care Act. It is not possible to classify data neatly into identifiable and non-identifiable categories. The identifiability of data covers a spectrum. At one end, the inclusion of variables such as names, addresses and postcodes poses a very high and obvious risk of identifiability. At the other end of the spectrum, the release of highly aggregated data (for example, total number of cancers registered in the South West during the period 1998-2000) poses no realistic risk of identifiability. Between these two extremes, the disclosure of anonymised but individual records, or data relating to small populations or small numbers of people, poses some risk of identifiability. For example, in a large village of around 1500 residents it is quite possible that there is only one male resident aged over 90. We would not publish cancer statistics for that area which that said that in men aged 90+ there had been one case of cancer. This would be disclosing confidential medical information about that person. There are clear risks of disclosing identifiable data in the publication of data that refers to small populations or small numbers of people. Any possibility, no matter how small, that a vulnerable individual could be harmed by the publication of data must be taken seriously. The simple solution would be to eliminate all risk and release only highly aggregated data. This solution would restrict considerably the data that cancer registries would be able to publish to the extent that the data would lose value e.g., for planning services for rare cancers. In order to strike some balance, the data release policy for cancer registries states that data based on fewer than 5 patients or on a population of less than 1000 should be regarded as potentially identifiable and should not be released in standard reports. In practice, this means that the release of cancer data at the level of electoral wards or smaller geographical areas is restricted. Researchers wishing to use identifiable cancer registry data for research purposes must apply to PIAG and to a medical research ethics committee to gain approval for their work.

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cancer incidence in plymouth€¦ · 1), which shows the incidence of lung cancer across the five...

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