Tor Haldorsen

Smoking habits and risk of cancers other than lung cancer: 28 years' follow-up of 26,000 Norwegian men and women.

The impact of tobacco smoking on lung cancer risk has been investigated thoroughly since the 1950s, but other types of cancer also have been associated with smoking. In the present study, the aim was to explore the variation in risk connected with cigarette, cigar, and pipe smoking of suspected smoking-associated cancers other than lung cancer. Data were obtained from a survey of a random sample of the Norwegian population. A self-administered mailed questionnaire, which included questions about smoking habits, was completed by 26,000 men and women in 1965 (response rate: 76 percent). The cohort was followed from 1966 through 1993, including registration of all incident cancer cases. A dose-response relationship of cigarette smoking to the risk of urinary bladder cancer and cancers of the upper digestive and respiratory tract was observed. For the latter forms of cancer, a dose-response relationship of pipe smoking also was observed. In cancer of the pancreas, a stronger association between cigarette smoking and cancer risk was observed when the analysis was confined to histologically confirmed cases only. Current cigarette smokers at baseline had a significantly higher risk of cervical cancer than those who never smoked cigarettes. In cancers of the stomach, colon, rectum, breast, corpus uteri, ovary, and prostate, and in leukemia, no association between smoking and cancer risk was observed.

Incidence of cancer among Nordic airline pilots over five decades: occupational cohort study

Abstract Objective: To assess the incidence of cancer among male airline pilots in the Nordic countries, with special reference to risk related to cosmic radiation. Design: Retrospective cohort study, with follow up of cancer incidence through the national cancer registries. Setting: Denmark, Finland, Iceland, Norway, and Sweden. Participants: 10 032 male airline pilots, with an average follow up of 17 years. Main outcome measures: Standardised incidence ratios, with expected numbers based on national cancer incidence rates; dose-response analysis using Poisson regression. Results: 466 cases of cancer were diagnosed compared with 456 expected. The only significantly increased standardised incidence ratios were for skin cancer: melanoma 2.3 (95% confidence interval 1.7 to 3.0), non-melanoma 2.1 (1.7 to 2.8), basal cell carcinoma 2.5 (1.9 to 3.2). The relative risk of skin cancers increased with the estimated radiation dose. The relative risk of prostate cancer increased with increasing number of flight hours in long distance aircraft. Conclusions: This study does not indicate a marked increase in cancer risk attributable to cosmic radiation, although some influence of cosmic radiation on skin cancer cannot be entirely excluded. The suggestion of an association between number of long distance flights (possibly related to circadian hormonal disturbances) and prostate cancer needs to be confirmed.

The impact of smoking habits on lung cancer risk: 28 years' observation of 26,000 Norwegian men and women

While factory-made cigarettes dominate the market in most countries, the use of handrolled cigarettes accounts for a substantial proportion of the tobacco consumption in Norway. In the present study, we examined the impact of tobacco smoking on lung cancer in general, and the effect of handrolled cigarettes in particular. The data used was from a self-administered mailed questionnaire which included questions about smoking habits and which was completed by about 26,000 men and women in 1964–65. During the follow-up from 1966 to 1993, 333 lung cancers in men and 102 in women were registered. The analysis was performed by use of the Cox proportional hazards regression models. A clear dose-response relationship was found both for cigarette smoking, and for pipe smoking (in men). The dose-response relationship of cigarette smoking was seen in all the three histologic groups considered-squamous cell carcinoma, adenocarcinoma, and small cell carcinoma. The highest relative risks were noted in squamous cell and small cell carcinoma. A higher risk of lung cancer was found for cigarette-smoking women who started cigarette smoking before the age of 30 compared with similar groups of men. In a combined analysis of men and women, and elevated relative risk of 1.9 (95 percent confidence interval=1.2–3.3) was found for those smoking only handrolled cigarettes compared with those smoking factory-made filter cigarettes only.

The influence of mammographic screening on national trends in breast cancer incidence

Introducing an organized mammographic screening programme affects the breast cancer incidence rate in a population. The diagnosis is advanced in time, and initially, an increase will occur in the number of cases, followed by a drop in the rate when women leave the programme. The aim of this study was to quantify the potential effects that mammographic screening programmes have on breast cancer incidence. In addition, we wanted to investigate how the incidence of breast cancer varies between different birth cohorts, age groups and time periods in the five Nordic countries Finland, Denmark, Iceland, Norway and Sweden, adjusting for the effects of the screening programmes. Time trends were analysed over the period 1978–1997, using age–period–cohort models. In Sweden, the rates more than doubled (relative risk (RR)=2.20, 95% confidence interval (CI) 1.8–2.6) in women offered screening for the first time compared with women not offered screening. The risk remained elevated (RR=1.34, 95% CI 1.2–1.6) for women who were continued to be offered screening, compared with women who were not offered screening. Finally, the rates dropped (RR=0.68, 95% CI 0.6–0.8) when the women left the programme. This indicates that screening advances the time of diagnosis, which is a prerequisite to subsequent reduction in mortality. Analysis of secular trends, corrected for the influence of screening, showed that the rates in Finland increased by 13% per 5-year period, with a more modest increase in the other countries. There were strong cohort effects in all Nordic countries, and the risk seemed to be flattening for the youngest cohorts in most of the countries.

Relative Survival of Cancer Patients: A Comparison between Denmark and the other Nordic Countries

The results of a Nordic collaborative project revealed that Danish cancer patients had a poorer prognosis than patients in the other Nordic countries for some major cancer sites. The present study was undertaken to further explore the differences in survival between Denmark and the other Nordic countries. All cancer cases diagnosed in the Nordic countries during 1958 to 1991/92 were included in the analysis. Relative survival and excess mortality were calculated for intervals in the first five years after diagnosis. Since the 1950s, the prognosis of cancer patients has improved in all the countries, but more moderately in Denmark. For cancers of the stomach, colon, rectum, breast (female), and prostate, the Danish patients had a markedly lower relative survival than the patients in the other countries. They also had the lowest proportion of localized tumours. It appears that Danish cancer patients are diagnosed at a later stage of disease than patients in the other Nordic countries.

Norwegian case-control study testing the hypothesis that seafood increases the risk of thyroid cancer

The hypothesis that consumption of seafood increases the risk of thyroid cancer has been tested by means of a matched case-control study. Linking the file of the National Health Screening Service (NHSS) containing dietary information about 60,000 Norwegians with the 1955–89 thyroid-cancer file of the Cancer Registry, by means of the 11-digit person-number, resulted in 92 cases—each of whom was matched with five controls with regard to age, gender, and place of residence. Forty-eight cases had answered questions on diet before diagnosis; 44 did so after diagnosis. Exposure data on seafood and seafood-related vitamins were recovered from the NHSS files for all 552 subjects. Odds ratios (OR) were computed by means of conditional logistic regression analysis. Univariate analysis of the 48 sets in which the case had answered the dietary questionnaire prior to the thyroid cancer diagnosis, as well as of all 92 sets, indicate that regular users of cod-liver oil, fish liver, or fish sandwich-spread run a higher risk of thyroid cancer than irregular and nonusers, and people eating more fish dinners per week also run a higher risk of thyroid cancer. Stepwise regression analysis corroborates the study hypothesis by showing that these two seafood variables increase the risk of thyroid cancer significantly. On the other hand, the results of a simultaneous regression analysis of these two seafood variables and a dietary vitamin-D index-variable tend to reduce the tenability of the above-mentioned conclusion since none of the OR estimates (all greater than one) reached significance in this part of the statistical analysis.

Trends in incidence of ductal carcinoma in situ: The effect of a population-based screening programme

BACKGROUNDnThe incidence of ductal carcinoma in situ (DCIS) has increased substantially in the western world in recent decades. The aim of this study was to investigate the incidence according to grade distribution, age, and implementation of a population-based screening programme.nnnMETHODSnCases of primary pure DCIS (n = 3167) were obtained from the Cancer Registry of Norway. Poisson regression was used to estimate trends in incidence.nnnRESULTSnAge-adjusted incidence of DCIS increased from 4 to 11 per 100, 000 women-years from 1993 to 2007, in parallel with the implementation of screening. Higher incidence was observed among prevalent (IRR 3.3) and subsequent (IRR 2.8) invited women compared with those not invited. The proportion of DCIS among breast malignancies increased throughout the period, most markedly in the age range of screening.nnnCONCLUSIONnThe increased proportion of DCIS during the study period is probably due to improved diagnostics resulting from the implementation of population-based screening.

Overdiagnosis among women attending a population-based mammography screening program

Increased incidence of ductal carcinoma in situ (DCIS) and invasive breast cancer (IBC) after introduction of organized screening has prompted debate about overdiagnosis. The aim was to examine the excess in incidence of DCIS and IBC during the screening period and the deficit after women left the program, and thereby to estimate the proportion of overdiagnosis. Women invited to the Norwegian Breast Cancer Screening Program were analyzed for DCIS or IBC during the period 1995–2009. Incidence rate ratios (IRRs) were calculated for attended vs. never attended women. The IRRs were adjusted by Mantel‐Haenszel (MH) method and applied to a set of reference rates and a reference population to estimate the proportion of overdiagnosis during the womens lifespan after the age of 50 years. A total of 702,131 women were invited to the program. An excess of DCIS and IBC was observed among women who attended screening during the screening period; prevalently invited women aged 50–51 years had a MH IRR of 1.86 (95% CI 1.65–2.09) and subsequently invited women aged 52–69 years had a MH IRR of 1.56 (95% CI 1.45–1.68). In women aged 70–79 years, a deficit of 30% (MH IRR 0.70, 95% CI 0.62–0.80) was observed 1–10 years after they left the screening program. The estimated proportion of overdiagnosis varied from 10 to 20% depending on outcome and whether the women were invited or actually screened. The results highlight the need for individual data with longitudinal screening history and long‐term follow‐up as a basis for estimating overdiagnosis.

Exposure of children to residential magnetic fields in Norway: Is proximity to power lines an adequate predictor of exposure?

The aim of this work was to study the exposure to magnetic fields of children living at different distances from a power line and to evaluate how well theoretical calculations compared with actual exposure. Personal exposure instruments were carried for 24 h by 65 schoolchildren living 28-325 m from a 300 kV transmission line; the current load was 200-700 A. About half of the children attended a school far from the power line, whereas the other half attended a school located about 25 m from the line. Exposure to magnetic fields was analyzed for three categories of location: at home, at school, and at all other places. Time spent in bed was analyzed separately. The results indicated that children who lived close to a power line had a higher magnetic field exposure than other children. The power line was the most important source of exposure when the magnetic field due to the line was greater than about 0.2 microT. Exposure at school influenced the 24 h time-weighted average results considerably in those cases where the distance between home and power line was very different from the distance between school and power line. The calculated magnetic field, based on line configuration, current load, and distance between home and power line, corresponded reasonably well with the measured field. However, the correlation depends on whether home only or 24 h exposure is used in the analysis and on which school the children attended. The calculated magnetic field seems to be a reasonably good predictor of actual exposure and could be used in epidemiological studies, at least in Norway, where the electrical system normally results in less ground current than in most other countries.

Longchain serum fatty acids and risk of thyroid cancer: A population-based case-control study in Norway

Epidemiologic studies have shown an association between seafood consumption and risk of thyroid cancer. Fish meals increase the serum concentrations of the longchain fatty acids, eicosapentaenoic acid (20∶5,n-3) (EPA) and docosahexaenoic acid (22∶6,n-3) (DHA), for days. The hypothesis that serum concentrations of fatty acids may be associated with thyroid cancer risk therefore was tested in a population-based case-control study with 74 cases and 221 matched controls. Seventy-three cases with sera in the Norwegian serum bank (JANUS) were identified in the Norwegian Cancer Registry and matched with three controls, also in JANUS, on age, gender, place of residence, and time of blood sampling. Each case was matched with two controls. Serum concentrations of 11 longchain fatty acids were determined blindly by gas chromatography for all subjects. Controls were divided into three groups with increasing serum fatty acid concentrations, and odds ratios between cases and controls were estimated relative to the group with lowest serum level by univariate and multivariate analyses. The main finding was a significant inverse relation between the sum of arachidonic acid (20∶4,n-6) (AA) and DHA serum concentrations and thyroid cancer risk. The significance of this association was weakened when the analyses were restricted to the papillary type of thyroid carcinoma. It was of the same order of magnitude whether the period between blood sampling and diagnosis was greater than eight years, or eight or less years. High EPA/AA ratio, indicating consumption of fish fat, was not associated significantly with increased thyroid-cancer risk. These data indicate that the association between seafood ingestion and increased thyroid-cancer risk may not be caused by the marine fatty acids.