Alcohol intake is causally associated with cancers of the larynx, oral cavity, pharynx, oesophagus and liver. In all five Nordic countries, alcohol consumption increased substantially between 1965 (6.5 litres per adult per year) and 1975 (10 litres), but remained at about 10 litres between 1975 and 1985. The daily consumption of men during the period was substantially higher than that of women, and that of both men and women was higher in Denmark than in the other Nordic countries. In about 2000, an annual total of almost 1,300 cancer cases (1,000 in men and 300 in women) would be avoided if alcohol drinking were eliminated. This corresponds to about 29% of all alcohol-related cancers, i.e. in the oesophagus (37%), oral cavity and pharynx (33%), larynx (29%) and liver (15%). About 2% of all cancers in men and 1% in women in the Nordic countries around the year 2000 will be caused by the drinking habits of the respective populations.
Although several biological agents have been linked convincingly with increased risks for cancer in humans, only infection of the lower female genital tract with human papillomavirus (HPV) and colonization of the gastrointestinal tract with Helicobacter pylori are of importance for cancer occurrence in the Nordic countries. HPV types 16 and 18, and probably types 31 and 33, are causally linked with cervical cancer and H. pylori, a Gram-negative bacteria, with gastric cancer. The estimated prevalence of genital infections with oncogenic types of HPV among Nordic women and the associated risk estimates indicate that approximately 45% of all cervical cancers arising in the Nordic countries are caused by such infections. This will be equivalent to about 550 cases in these countries each year around 2000, or 1% of all cancers arising in these populations. Similarly, the 35% prevalence of persistent gastric infection with H. pylori in the adult Nordic population and the associated risk estimates indicate that some 58% of all gastric cancers in the Nordic countries are due to this bacteria. This will correspond to about 2,350 new cases annually around the year 2000, with 1,350 among men and 1,000 among women, or approximately 2% of all cancers arising in the Nordic population.
In the early 1980s, Doll and Peto estimated that about 35% of all deaths from cancer in the United States were attributable to dietary factors, with a margin of uncertainty ranging from 10 to 70%. Since then, several dietary factors, e.g. fat and meat, have been suggested to increase the risk for cancer, while other factors, e.g. fibre, fruit and vegetables, have been suggested to decrease the risk. The case-control and cohort studies have, however, given ambiguous results, and the overall evidence is far from conclusive. The major findings on dietary factors that increase risk have been reported from case-control studies, but have not been confirmed in large population-based cohort studies. Although the research in this area indicates that diet is important in cancer prevention, current knowledge does not allow reliable estimates of the numbers and proportions of cancers that could be avoided through well-described modifications of dietary habits. During the last 10 years, low physical activity has been pinpointed as a risk factor for cancers at various sites, especially the colon; however, the causal mechanism is still unknown. Obesity, defined as a body mass index of 30 or more, is consistently associated with endometrial and gall-bladder cancers in women and renal-cell cancer in both men and women. As the prevalence of obesity was between 5 and almost 20% in the Nordic populations in 1995, 625 cancer cases (310 endometrial cancers, 270 renal-cell cancers in men and women and 45 gall-bladder and bile-duct cancers among women) can be predicted in the Nordic countries around the year 2000 to be caused by obesity. This implies that about 1% of all cancers in Nordic women and less than 1% of those in Nordic men could be avoided around the year 2000 if a healthy body weight could be maintained by all inhabitants.
The well-described influence of several aspects of reproductive life on the risk for cancer in the reproductive organs has raised concern regarding the safety of exogenous hormones, particularly since sex hormones have become one of the most widely used drugs among women in the western world. The major areas of application include oral contraception and hormone replacement therapy in women with menopausal symptoms. Since the introduction of oral contraceptives onto the Nordic market in the late 1960s, the number of users has grown steadily, to reach proportions of long-term users among women aged 15-45 years in 1985 ranging between 6% (Norway) and 19% (Sweden) and proportions of current users in 1994 ranging between 20% (Norway) and 28% (Sweden). Such data on the current and long-term use of oral contraceptives by the female populations, linked with relative estimates of adverse (cancers of the breast and uterine cervix) and beneficial effects (protection against cancers of the ovary and endometrium), indicate that 95 cases of breast cancer and 40 of cervical cancer will be caused by oral contraceptives annually around 2000 in the Nordic countries, which corresponds to 0.6% of all breast cancers and approximately 3% of all cervical cancers. The beneficial effects include an annual prevention around the year 2000 of approximately 350 cases of ovarian cancer and a similar number of endometrial cancer, for a total about 700 cancer cases annually. The prevalence of long-term users (> or = 5 years) of hormone replacement therapy among Nordic women aged 40-69 in 1995 was estimated to be 10-11%, which on the basis of an associated relative risk for breast cancer ranging from 1.2-1.5 suggests than an annual total of 260 cases of breast cancer could be avoided in the Nordic countries around the year 2000 if hormone replacement therapy were eliminated. This corresponds to 1.8% of all notified cases of breast cancer among women in these countries.
Exposure to solar and ionizing radiation increases the risk for cancer in humans. Some 5% of solar radiation is within the ultraviolet spectrum and may cause both malignant melanoma and non-melanocytic skin cancer; the latter is regarded as a benign disease and is accordingly not included in our estimation of avoidable cancers. Under the assumption that the rate of occurrence of malignant melanoma of the buttocks of both men and women and of the scalp of women would apply to all parts of the body in people completely unexposed to solar radiation, it was estimated that approximately 95% of all malignant melanomas arising in the Nordic populations around the year 2000 will be due to exposure to natural ultraviolet radiation, equivalent to an annual number of about 4700 cases, with 2100 in men and 2600 in women, or some 4% of all cancers notified. Exposure to ionizing radiation in the Nordic countries occurs at an average effective dose per capita per year of about 3 mSv (Iceland, 1.1 mSv) from natural sources, and about 1 mSv from man-made sources. While the natural sources are primarily radon in indoor air, natural radionuclides in food, cosmic radiation and gamma radiation from soil and building materials, the man-made sources are dominated by the diagnostic and therapeutic use of ionizing radiation. On the basis of measured levels of radon in Nordic dwellings and associated risk estimates for lung cancer derived from well-conducted epidemiological studies, we estimated that about 180 cases of lung cancer (1% of all lung cancer cases) per year could be avoided in the Nordic countries around the year 2000 if indoor exposure to radon were eliminated, and that an additional 720 cases (6%) could be avoided annually if either radon or tobacco smoking were eliminated. Similarly, it was estimated that the exposure of the Nordic populations to natural sources of ionizing radiation other than radon and to medical sources will each give rise to an annual total of 2120 cancers at various sites. For all types of ionizing radiation, the annual total will be 4420 cancer cases, or 3.9% of all cancers arising in the Nordic populations, with 3.4% in men and 4.4% in women.
Active smoking is causally associated with cancers of the lung, larynx, oral cavity, pharynx, oesophagus, pancreas, renal parenchyma, renal pelvis and urinary bladder, and passive smoking appears to be causally associated with cancer of the lung. Information on smoking habits for the years 1965, 1975 and 1985 shows that more men than women in the Nordic countries were current smokers. The rates of women were stable over time and those of men were decreasing, approaching those of women. Lung cancer, in particular, is strongly associated with active smoking: by increasing the number of cigarettes smoked per day (lifelong) to 5, 10, 20 and 40 or more, the risk increases by five-, eight-, 16- and 30-fold, respectively, over that of people who have never smoked. Thus, with approximately 35% current smokers and 25% former smokers among Nordic men in 1985 and approximately 30% current smokers and 15% former smokers among Nordic women in that year, by the year 2000 10,000 cases of lung cancer (6,500 in men and 3,500 in women) will be caused by active smoking; this is equivalent to 82% of all cases of lung cancer in these populations. Another 6,000 cancers of other types (4,000 in men and 2,000 in women) are caused annually by active smoking, yielding a total of 16,000 new cases each year around the turn of the century. This implies that 14% (19% in men and 9% in women) of all incident cancers in the Nordic countries around the year 2000 will be caused by active tobacco smoking. In comparison, passive smoking is a minor cause of lung cancer, responsible for approximately 0.6% of all new cases (approximately 70 cases annually) in this area around the turn of the century.
A population-based study was carried out on 3,988 tumours in teenagers (aged 10-19 years) diagnosed during the period 1943-87 in Denmark and abstracted from the files of the National Cancer Registry. In that Registry, codes for tumours were based solely on topography until the end of 1977. In order to obtain a uniform data set, coded by the system of the International Classification of Diseases for Oncology (ICD-O) now used at the Cancer Registry, all cases of teenage cancer diagnosed prior to 1978 were re-evaluated, and an ICD-O code was applied. Tumours were further aggregated into diagnostic groups using an internationally agreed scheme. The average incidence rates for all histological types combined were 136 per million for boys and 108 per million for girls, which are close to those reported in Connecticut, USA. Central nervous system tumours, leukaemia and malignant lymphomas accounted for 60% of all cancers among teenagers. An overall excess of cancers among boys was mainly due to more frequent occurrence of leukaemias, malignant lymphomas, sarcomas and germ-cell tumours. Increasing trends with time were seen for malignant lymphomas in both boys and girls and for subtypes of non-seminoma germ-cell tumour among boys aged 15-19. For other diagnostic groups, including the main group of leukaemias, the rates have remained largely unchanged, suggesting that environmental factors associated with modern society play a minor role in the aetiology of cancer among teenagers.
INTRODUCTION: The aim of the study was to estimate the preventable potential of various types of cancer in Denmark on the basis of present knowledge. MATERIAL AND METHODS: The well-documented factors in lifestyle and environment causing cancer in Denmark were identified from the IARC Monograph series. The population attributable risk per cent (PAR%) and the annual number of preventable cancers were calculated for each aetiology and cancer type around the year 2000. RESULTS: A large proportion of the cancers occurring in the lungs, larynx, upper digestive tract, skin, lower urinary tract, and the uterine cervix is potentially avoidable, whereas only a small proportion of breast and colorectal cancers is preventable on the given knowledge. The main causative factors include active and passive smoking, alcohol intake, exposure to asbestos and other occupational carcinogens, solar and ionising radiation, obesity, human papillomavirus infection in the female genital tract, and infection with Helicobacter pylori. More than 5000 cancers in men and almost 3500 in women annually in Denmark could have been avoided by eliminating exposure to these known carcinogens. This is equivalent to 39% and 23% of all cancers occurring respectively in men and women, around the year 2000. Smoking habits account for more than half of these avoidable cases. DISCUSSION: The incidence of cancer could be greatly reduced through primary prevention, especially of tobacco smoking, which is the major single factor. A large proportion of the cancers occurring in the lungs, larynx, upper digestive tract, skin, lower urinary tract, and the uterine cervix are potentially avoidable. More research in the field of aetiological factors causing female breast cancer and colorectal cancer is much needed in order to be able to prevent these types of cancer.
BACKGROUND: In some rare inherited disorders such as Li-Fraumeni syndrome, relatives of children with cancer are at increased risk of cancer. We aimed to assess relations between childhood cancer and sibling risk, and evaluate the influence of recessive conditions in cancer causation. METHODS: We did a population-based cohort study in the Nordic countries of 42277 siblings of 25605 children with cancer. Children with cancer were identified from records in the five Nordic cancer registries, and their siblings from nationwide population registries. Cancers in siblings were documented through record linkage with cancer registries and compared with national incidence rates. We also assessed cancer incidence in parents to identify familial cancer syndromes. FINDINGS: 284.2 cancers were expected in siblings, whereas 353 were diagnosed (standardised incidence ratio 1.24 95% CI 1.12-1.38). Risk ratios for siblings were highest in the first decade of life (2.59, 1.89-3.46). We excluded 56 families with genetic syndromes linked to cancer, which reduced this ratio from 1.7 to 1.0 (0.7-1.3) for siblings younger than 20 years, and from 1.3 to 1.0 (0.8-1.3) for those aged 20-29 years. We found no new patterns of familial cancer that indicated inherited susceptibility, or evidence that recessive conditions might contribute to cancers not explained by syndromes. 40% of cancers in siblings that occurred before age 20 years could be attributed to known genetic factors, whereas 60% remained unexplained. INTERPRETATION: Apart from rare cancer syndromes, paediatric cancer is not an indicator of increased cancer risk in siblings.