1 Northern and Yorkshire Cancer Registry and Information Service, Leeds; 2 University of Leeds, Leeds; 3 Scottish Cancer Intelligence Unit, Information and Statistics Division, National Health Service Scotland, Edinburgh; 4 Thames Cancer Registry, Kings College, London; 5 London School of Hygiene and Tropical Medicine, London; 6 National Cancer Intelligence Centre, Office for National Statistics, London, UK; 7 Istituto Superiore di Sanità, Rome; 8 Istituto Nazionale per lo Studio e la Cura dei Tumori, Milan, Italy
Received 26 August 2002; revised 25 November 2002; accepted 13 January 2003
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Abstract |
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Cancer incidence, mortality and survival statistics for the UK are routinely available; however, data on prevalence, which is generally regarded as an important measure for health planning and resource allocation, are relatively scarce.
Materials and methods:
Eight cancer registries in the UK, covering more than half the population, provided data based on >1.5 million cases of cancer. Total prevalence was calculated using methods developed for the EUROPREVAL study, based on modelling incidence and survival trends. The prevalence of cancers of the stomach, colon, rectum, lung, breast (in females), cervix uteri, corpus uteri and prostate, melanoma of skin, Hodgkins disease, leukaemia and all malignant neoplasms combined, was estimated for the UK for the end of 1992.
Results:
Overall, 1.5% of males and 2.5% of females in the UK population at the end of 1992 were living with a diagnosis of cancer. These proportions increased steeply with age, with
7.5% (7.3% and 7.8%, in males and females, respectively) of people aged
65 years living with a diagnosis of cancer. Of the individual cancers, by far the highest prevalence (almost 1%) was seen for breast cancer in females; more than one in three of all living female cancer patients had been diagnosed with breast cancer. For males, around half of prevalent cases had been diagnosed >5 years previously and 30% >10 years previously; for females, these figures were both higher, at
60% and 40%, respectively.
Conclusions:
The estimates of prevalence presented here comprise: recently diagnosed patients in need of treatment and monitoring; long-term survivors, some of whom will nevertheless eventually die from the cancer, while others may be cured of the disease; and patients in the terminal phase who are dying from the cancer. Further work should attempt to identify the proportions of patients in the different phases of care in order to optimise the use of prevalence estimates in health care planning.
Key words: cancer, cancer registry, prevalence, UK
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Introduction |
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Three- and ten-year cancer prevalence figures have recently been published for England and Wales for patients alive in January 1993 and diagnosed in 19901992 and 19831992, respectively [1], using incidence data and follow-up for death or emigration. This is the directly observed 3- or 10-year prevalence. Total prevalence is all those cases alive at a given date, i.e. those directly observed by a cancer registry plus those that were diagnosed before the registry started. The methodology developed by the collaborative EUROPREVAL study [4] provided an opportunity to estimate the total UK prevalence to the same follow-up date (the end of 1992) for 11 sites of cancer and for all malignant cancers combined. This enabled the estimation of the total burden of cancer within the UK by sex, age group and time since diagnosis that is presented in this paper. The EUROPREVAL estimates were validated by comparing them with the directly observed figures for England and Wales.
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Materials and methods |
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The data from the seven geographically widespread registries in England related to 53% of the English population; this population had a very similar age distribution to that of England as a whole. The Scottish Cancer Registry covered the whole of the Scottish population. In order to obtain UK figures, we assumed first that the cancer prevalence in the English registries covered by EUROPREVAL was representative of England and Wales as a whole. For Northern Ireland, the prevalence estimates of cancer in Scotland were applied to the population estimates for Northern Ireland, which contains only 3% of the total UK population. The data were analysed in three age groups (044, 4564 and
65 years) to enable adjustment of the overall prevalence estimates for any differences in age structure between populations.
Calculation of observed prevalence
Observed prevalence has been computed on the basis of the longest period of data available from each single registry, by means of the counting method implemented by PREVAL software [6]. Observed prevalence was then corrected to take account of the (small) contribution of cases lost to follow-up, by assigning to them a survival probability equal to that of patients successfully followed up of the same sex and with similar age and period of diagnosis [5, 6].
Calculation of total prevalence
Total prevalence figures for each cancer site were derived by applying an estimated correction factor, the completeness index (R) [7], defined as the proportion of the total prevalence represented by the observed prevalence. This varies according to the length of the registration period and the characteristics of the cancer being considered (mainly incidence and survival trends). Total prevalence derived by the completeness index method was recently validated using data from the Connecticut Cancer Registry for a group of different cancer sites [8].
The calculation of the completeness index is based on modelling incidence and survival trends with simple parametric functions [4, 9]. A single cancer-specific incidence trend was assumed for fitting data from the UK registries, while for the survival models, registry-specific relative risks were estimated. The periods of time covered by the EUROCARE data, used for estimation of survival trends, were not adequate to correctly estimate the required incidence and survival trends by age for cancer of the cervix uteri and for Hodgkins disease [4]; consequently, R values and hence the total prevalence could not be produced for these two malignancies, although the method allows an adjustment of the observed prevalence that furnished estimates of the 15-year prevalence.
The completeness indices that were used in the subsequent calculations of prevalence are shown in Table 2 for the different populations and types of cancer. They were generally higher for males than for females, e.g. for all cancers the indices were 0.8 and
0.7, respectively.
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Results |
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The numbers of prevalent cases of cancers of stomach, colon, rectum, lung, uterus and prostate were all dominated by those in the oldest age group (65 years), >70% of cases being in this category (Table 4). This contrasts with the prevalence of melanoma, breast and cervix cancers that were more influenced by cases in middle age (4564 years).
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Discussion |
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Breast cancer dominates the pattern of cancer prevalence for females because it is the most commonly diagnosed tumour and, even before the introduction of breast screening in the UK in 1988, it had a five-year relative survival of 65% [10]. More than one in three of all living female cancer patients had been diagnosed with breast cancer. Although lung cancer has long been the most common cancer in UK males, the poor prognosis means that it makes only a small contribution (<10%) to overall cancer prevalence in males. No single site of cancer dominates the male prevalence pattern, although prostate cancer, which is the most common site overall, has by far the highest rate in the >65 years age group.
Approximately one half of all living male cancer patients had survived for >5 years and one-third had survived for >10 years. For females, these proportions were higher at 60% and
40%. The problems associated with cancer management are usually considered for the years immediately following diagnosis, whereas the majority of patients have been living with their disease for at least 5 years. Not all of these survivors are diagnosed with cancers that have good prognosis; thus, for both lung and stomach cancer, in both sexes, >30% of the prevalent cases had survived for >10 years. This apparent anomaly is, at least partly, explained by the relatively very high incidence rates for these cancers in the 1960s and 1970s such that a small fraction of long-term survivors can make a substantial contribution to current prevalence.
The annual number of new cancer cases diagnosed in the UK (excluding non-melanoma skin cancer) was 252 000 in 1992 and this increased to 263 000 cases by 1998. The corresponding numbers of cancer deaths were 164 000 and 154 000, respectively. The estimated total number of prevalent cases on 31 December 1992 was 1 178 000 (applying the all cancers, all ages prevalence proportions per 100 000, provided in Table 3, of 1506 for males and 2534 for females to the 1992 UK population of 28.362 million males and 29.645 million females). The ratio of prevalence to incidence was thus
5-fold, and the ratio of incidence to mortality
1.5-fold in 1992. With generally rising incidence, gradual improvement in cancer care and increasing survival of cancer patients, prevalence will gradually increase; mortality from cancer will continue to decrease if the improvements in survival more than counterbalance the increases in incidence.
The large and increasing size of the population of living cancer patients emphasises the magnitude of the impact of cancer on peoples lives, either as patients themselves or as relatives of cancer patients, but the relevance of prevalence figures to the planning of cancer care is less obvious. The number of new cases in a year is an indicator of the need for resources for diagnostic investigations and first-line treatment. Similarly, the annual number of cancer deaths is an indicator of the need for resources for palliation and terminal care. Prevalence is a composite measure of a highly heterogeneous population comprised of: recently diagnosed patients in need of treatment and monitoring; long-term survivors, some of whom will nevertheless eventually die from the cancer, while others may be cured of the disease; and patients in the terminal phase who are dying from the cancer. Direct estimates of the average costs in each phase of cancer care have been obtained by linking incidence registry data with administrative databases [1315]. Treatment costs are strongly related to age, cancer type and stage of disease at diagnosis [13]. The costs of surveillance and monitoring activities needed in the intermediate phase are much lower than costs for first and terminal treatment but, as they may continue for a long period of time, their impact on the total cost of cancer care is not negligible.
Further work on the development of the definition of prevalence should attempt to identify subgroups of patients in the different phases of care. The disaggregation of prevalence by time since diagnosis (as in this paper) is a first step in this direction. Prevalence by stage of disease at diagnosis would be an additional and very informative indicator of the need for care. Recent developments in cancer survival analysis [16] can, for some types of cancer, distinguish long-term survivors who are cured and those who will die from their cancer. This may lead to more detailed assessments of prevalence in the future.
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Acknowledgements |
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Footnotes |
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References |
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