Denmark
Hans H Storm
Situated like a cork in a bottle in the Baltic Sea, with the peninsula Jutland attached to Germany in the south and islands between it and Sweden to the east and Norway to the north, Denmark is geographically and historically the most central country in the northern part of Europe. Its physical location in ancient times meant that those controlling the narrow straits (the Sound and the Great Belt) also controlled trade and traffic into the Baltic Sea. Hence battles between Denmark and its neighbours are part of the history, while peaceful coexistence and collaboration is today's reality. The climate is coastal with frequent light rains (about 50 mm per month) and with winter temperatures approaching zero centigrade and summer temperatures in the mid twenties. The well-educated literate population of 5.2 million occupy only 40,000 km2. Hence, Denmark is one of the most densely populated countries in Europe with about 120 inhabitants per km2. While 554,000 inhabit central Copenhagen, and 604,000 live in Copenhagen County, the remainder of the population is scattered around in numerous minor and 12 towns with over 40,000 inhabitants on the islands and the peninsula of Jutland. The country is essentially flat, the highest points today being the pylons (254 m) of the 6.8 km long suspension bridge over the eastern part of the Great Belt between Zealand and Funen. This bridge is the last of numerous bridges that tie the kingdom together. Agriculture accounts for 5% of the GNP, which in 1991 was 21,461 USD per capita, industry for 29% and services for 66%. Life expectancy is somewhat lower than among the closest northern neighbours with 73 years for men and 79 for women in 1991, even if infant mortality is low (6/1000). The life expectancy has remained at the same level during the last decade, and reflects premature death due to diseases related to a high prevalence of smoking in both men and women and other risk behaviours leading to cancer and cardiovascular diseases. The leading causes of deaths in 1993 were cardiovascular diseases (43%), followed by cancer (25%).
Cancer registration
The Danish Cancer Registry is population based covering all of Denmark with incidence data on cancer since 1943. Mandatory reporting of cancer and some benign tumours (notably the bladder and the central nervous system) was introduced by administrative order in 1987. From 1988 the National Patient Discharge Registry has been used as an additional source of data to the notification forms received from hospitals and practising physicians. Institutes of pathology used to report only cancers found in autopsies. Nevertheless, the validity of the data on morphology is high, and about 92% of all cases are histologically confirmed. However, with the establishment of the National Registry for Pathology in 2000, data on cancer morphology are received both from clinicians and from pathologists. Since its inception the Registry has routinely linked with death certificates and recorded date of death and used death certificates as a basis for tracing cancers not reported by regular means. The cases known only from death certificates have been below 5% since the 1950s and in the recent decades at about 1-2%. About 8% of the annual incidence is first reported to the registry on a death certificate. Data on individual cancer patients are available in the detail of the 7th revision of the International Classification of Diseases (ICD) for all years, and since 1978 also according to the ICD-O (International Classifications of Diseases for Oncology [1]). A core set of data is kept on each individual including date of birth, sex, date of cancer, diagnosis, method of verification, date of death and cause of death. The place of residence at the time of diagnosis has since 1968 been at the level of commune (274 communes) as the smallest administrative area. Prior to that, it was registered only at the level of County (16 counties 1968) with an indication of whether it was a rural or an urban area. Research activities by the registry staff since its inception kept the completeness and validity of the data 1943-1996 high. The completeness [2] and validity [3] were assessed to be in the order of 95-98% by linkage to independent (redundant) data from the hospital discharge registry system, death certificates and a pathology register. The registry operations include extensive quality control and verification procedures. The coding process includes independent review of all coded cases and is supervised by medical doctors. Computerised checks not only search for trivial logic errors like unusual sex, site, morphology, stage and treatment combinations, but also warn about rare combinations of these variables. Ambiguous information (either within one notification form or between forms) leads to queries on approximately 10% of notifications received, and the quality control procedures account for about half of the staff time used in the registry. The registry does not perform random reabstraction as a routine quality control measure. However, this is done indirectly via the research projects using the registry as a sampling frame. So far these projects have indicated that the registry is of high quality but not without errors and definition problems during 50 years of operation [4-6]. Incidence reports are published regularly [7-8], and since 1978 annual publications have enumerated cancer in Denmark with a commentary and description of the cancer registry, quality etc. [9]. A detailed description of the Cancer Registry history and procedures and its research was published recently [10-11]. In addition a number of major publications have dealt with multiple primary cancer [12], where Denmark follows the rules specified by the International Association of Cancer Registries, survival [13], cancer maps [14-15], cancer in the Nordic Countries [16-17] including predictions of both cancer incidence [18] and mortality [19]. Smoking related cancers such as cancers of the lungs, bladder and upper respiratory tract have increased in both men and women. Recently, the rate of male lung cancer seems to have reached a maximum level and has decreased slightly, which tallies with the fact that the prevalence of smoking in young men particularly is lower today than before. Unfortunately the same trend is not seen among women where the incidence is on a rapid increase. Cancers related to the consumption of alcohol and diet such as oesophagus and colon are also increasing, as is malignant melanoma. This is in accordance with the present lifestyle and welfare in Denmark. Breast cancer in women is steadily increasing, which is seen in conjunction with a relatively low birth rate and late first time pregnancies. Screening for breast cancer is at present only offered in two counties. A high incidence of cervical cancer in women in the 1960s is now low following the introduction of screening programs in all counties. Stomach cancer is decreasing in both men and women, as is seen in most developed countries. A National death index has existed in computerised form since 1943. A uniform system, coded according to ICD-8 with some local additions has existed in computerised form from 1971 onwards. Data from this part of the National Death Index were used for presentation in this publication. Death certificates are issued by a physician known to the patient, in accordance with international rules. Until 1997 all death certificates were checked by the medical officer of the county, and corrections were mailed to the National Board of Health for coding and data entry. Death certificates on cancer patients have been checked in two crosssectional studies, and their quality has been satisfactory, with over 80% correct diagnosis and completeness [20]. However, for some sites it is obvious from the registry procedures that the official cause of death often is in error. E.g., more lung cancer deaths occur in Denmark than accepted incident cases.
References
1. World Health Organization. International Classification of Diseases for Oncology. WHO, Geneva 1976.
2. Østerlind A, Jensen OM. Evaluering af cancerregistreringen i Danmark 1977: en præliminær evaluering af Cancerregisterets og Landspatientregisterets registrering af cancertilfælde. Ugeskr Laeger 1985;147:2483-8 (in Danish).
3. Ministry of Health working group on Cancer Registration. Proposal to a modernised update of the Cancer Registry. Ministry of Health, Copenhagen 1995 (in Danish).
4. Storm HH. Completeness of cancer registration in Denmark 1943-1966 and efficacy of record linkage procedures. Int J Epid 1988;17:44-9.
5. Holm NV, Hauge M, Jensen OM. Studies of cancer aetiology in a complete twin population: Breast cancer, colorectal cancer and leukaemia. Cancer Surv 1982;1:17-32.
6. Krasnik M, Frølund C, Rosenstock S, Franzman MB, Storm HH. Forekomst af lungekræft i Danmark 1943-1986. Ugeskr Laeger 1994;156:3021-5 (in Danish).
7. Clemmesen J. Statistical studies in malignant neoplasms I-V. Acta Pathol Microbiol Scand 1964-1977; Suppl. 174, 209, 247, 261.
8. Danish Cancer Registry. Incidence of cancer in Denmark 1973-1977. Danish Cancer Society, Copenhagen 1982.
9. Storm HH, Michelsen E, Pihl J, Larsen AL. Cancer incidence in Denmark 1993. Danish Cancer Society, Copenhagen 1996.
10. Storm HH. The Danish Cancer Registry, a self-reporting national cancer registration system with elements of active data collection. In: Jensen OM, Parkin DM, MacLennan R, Muir CS, Skeet RG (eds). Cancer Registration Principles and Methods. IARC Sci Publ 95, Lyon 1991, 220-36.
11. Storm HH, Michelsen EV, Clemmensen IH, Pihl J. The Danish Cancer Registry - history, content, quality and use. Danish Medical Bulletin 1997;44:549-53.
12. Boice JD Jr, Storm HH, Curtis RE, Jensen OM, Kleinerman RA, Jensen HS, Flannery JT, Fraumeni JF Jr. Multiple primary cancers in Connecticut and Denmark. Natl Cancer Inst Monogr 68, 1985.
13. Carstensen B, Storm HH, Schou G. Survival of Danish cancer patients 1943-1987, APMIS 1993;101: Suppl 33.
14. Carstensen B, Jensen OM. Atlas of cancer incidence in Denmark, 1970-79. Danish Cancer Society, Copenhagen 1986.
15. Jensen OM, Carstensen B, Glattre E, Malker B, Pukkala E, Tulinius H. Atlas of cancer incidence in the Nordic Countries. Nordic Cancer Union, Munksgaard, Copenhagen 1988.
16. Hakulinen T, Andersen A, Malker B, Pukkala E, Schou G, Tulinius H. Trends in cancer incidence in the Nordic countries. APMIS 1986;94: Suppl 288.
17. Tulinius H, Storm HH, Pukkala E, Andersen A, Ericsson J. Cancer incidence in the Nordic Countries, 1981-86. APMIS 1992:100; Suppl 31.
18. Engeland A, Haldorsen T, Tretli S, Hakulinen T, Hörte LG, Luostarinen T, Magnus K, Schou G, Sigvaldason H, Storm HH, Tulinius H, Vaittinen P. Prediction of cancer incidence in the Nordic countries up to years 2000 and 2010. APMIS 1993;101: Suppl. 38.
19. Engeland A, Haldorsen T, Tretli S, Hakulinen T, Hørte LG, Luostarinen T, Schou G, Sigvaldason H, Storm HH, Tulinius H, Vaittinen P. Prediction of cancer mortality in the Nordic countries up to years 2000 and 2010. APMIS 1995;103: Suppl 49.
20. Storm HH. Validity of death certificates for cancer patients in Denmark 1977. Danish Cancer Society, Copenhagen 1984.