Several large epidemiological studies in the Nordic countries have failed to confirm an association between age at first birth and breast cancer independent of parity. To assess whether lack of power or heterogeneity between the countries could explain this, a meta-analysis was performed of 8 population-based studies (3 cohort and 5 case-control) of breast cancer and reproductive variables in the Nordic countries, including a total of 5,568 cases. It confirmed that low parity and late age at first birth are significant and independent determinants of breast-cancer risk. Nulliparity was associated with a 30% increase in risk compared with parous women, and for every 2 births, the risk was reduced by about 16%. There was a significant trend of increasing risk with increasing age at first birth, women giving first birth after the age of 35 years having a 40% increased risk compared to those with a first birth before the age of 20 years. Tests for heterogeneity between studies were not significant for any of the examined variables. In the absence of bias, this suggests that several individual Nordic studies may have had too little power to detect the weak effect of age at first birth observed in the meta-analysis.
The effect of age at first pregnancy and number of pregnancies was examined in a cohort of 14,421 women where reproductive informations were collected as part of a cervical cancer screening program. A total of 352 cases occurred in the cohort. In subgroups of women defined by age at first pregnancy the relative risk of breast cancer was lower among women who were first pregnant before 25 years of age (RR = 0.85 vs 1.20). In subgroups of women defined by parity the relative risk decreased with increasing number of pregnancies from about unity among women with 0-3 pregnancies to 0.7 among women with 6 or more pregnancies.
Many case reports have suggested an association between Klinefelter syndrome (KS) and cancer, but studies of the cancer incidence in larger groups of men with KS are lacking. A cohort of 696 men with KS was established from the Danish Cytogenetic Register. Information on the cancer incidence in the cohort was obtained from the Danish Cancer Registry and compared with the expected number calculated from the age, period and site specific cancer rates for Danish men. A total of 39 neoplasms were diagnosed (relative risk = 1.1). Four mediastinal tumours were observed (relative risk = 67); all four were malignant germ cell tumours. No cases of breast cancer or testis cancer were observed. One case of prostate cancer occurred within a previously irradiated field. No excess of leukaemia or lymphoma was found. An increased risk of cancer occurred in the age group 15-30 years (relative risk = 2.7). All six tumours in this group were germ cell tumours or sarcomas. The overall cancer incidence is not increased and no routine cancer screening seems to be justified. A considerably elevated risk of mediastinal germ cell tumours occurs in the period from early adolescence until the age of 30.
Nation-wide incidence rates are presented of colorectal cancer in Denmark from 1943 to 1988. In Denmark notification of malignant and related diseases is mandatory. The percentage of histologically confirmed tumours is now 95. The annual incidence rate of colon cancer in Denmark has been increasing among men and women combined from 684 cases in 1943-1947 to 2020 cases in 1988. In the same period the incidence of rectal cancer has increased from 762 cases in 1943-1947 to 1108 cases in 1988. We analyzed the effects of age, calender time, and birth cohort with multiplicative Poisson models. We did not find consistent period effects in the models. We suggest an etiologic distinction between carcinoma of the rectum, the left colon and the right colon.
Nation-wide incidence rates are presented of colorectal cancer in Denmark from 1943 to 1988. In Denmark notification of malignant and related diseases is mandatory. The percentage of histologically confirmed tumours is now 95. The annual incidence rate of colon cancer in Denmark has been increasing among men and women combined from 684 cases in 1943-47 to 2020 cases in 1988. In the same period the incidence of rectal cancer has been increasing from 762 cases in 1943-47 to 1108 cases in 1988. We analyzed the effects of age, calendar time, and birth cohort with multiplicative Poisson models. We did not find consistent period effects in the models. We suggest the trends in colorectal cancer incidence rates may be due to changes in environmental factors such as dietary habits and in physical activity. Furthermore, we suggest an etiologic distinction between carcinoma of the rectum, the left colon and the right colon.
The role of diet in the aetiology of renal cell carcinoma was investigated in a population-based case-control study in Denmark. Cases were 20-79 years old, with a histologically verified diagnosis of renal cell carcinoma. Controls were sampled from the general population and were frequency-matched on age and sex. A total of 351 cases (73% of the eligible) and 340 controls (68% of the eligible) were included in the study. Dietary information was obtained in a self-administered food frequency questionnaire and the information was confirmed in a subsequent interview performed by trained interviewers who also elicited information on other suspected risk factors such as smoking, occupation, medical history, education and reproductive history. Logistic regression models were used to calculate the odds ratios, and, both frequency of consumption of various food stuffs and computed nutrients were examined. A positive association was observed between risk of renal cell carcinoma and total energy intake (odds ratio, OR, for highest quartile compared to lowest: 1.7 (95% confidence interval, CI, 1.0-3.0) for men, and 3.5 (95% CI 1.6-6.5) for women), fat intake (OR for highest quartile compared to lowest: 1.9 (95% CI 1.1-3.5) for men, and 3.3 (95% CI 1.6-6.9) for women). For women, an effect was also seen for intake of carbohydrates (OR for highest quartile compared to lowest: 3.2 (95% CI 1.5-6.8), while no protective effect was seen for vegetables or fruit. Dairy products may be associated with risk of renal cell cancer (OR for women using thickly spread butter compared to thinly spread: 11.4 (95% CI 2.8-45), OR for women who drank more than one glass of milk with 3.5% fat content compared to never drink milk: 3.7 (95% CI 1.2-11). As expected, total energy intake, intake of fat, protein and carbohydrates were closely correlated making it difficult to identify one of the energy sources as more closely associated with risk of renal cell cancer than the other. Several energy sources have been identified as possible risk factors for renal cell carcinoma. It is possible that a high energy intake as such rather than the individual sources are responsible for the increased risk. Furthermore, dairy fats may be associated with renal cell carcinoma risk. The observed associations appeared stronger in women, and did not explain the association with obesity and low socio-economic status previously found in Denmark.
Multiplicative Poisson models were used to identify subgroups of the Danish population at high and low risk of developing cancer of the right or left side of the colon, and cancer of the rectum. The analysis was based on cross-linked data from the 1970 census and the Danish Cancer Registry, where a 10-year follow-up period yielded some 20,000 colo-rectal cancers, in approximately 2.5 million persons. The risk of cancer of the right side of the colon in longer educated men living in apartment houses was almost twice as high as in farmers living in single family houses (relative risk 1.84; 95% confidence interval 1.42-2.37). A two-fold ratio (RR 2.18; 95% CI 1.70-2.62) was also seen in the risk of cancer of the left side of the colon between men with longer education in Greater Copenhagen and farmers in Jutland. The annual number of colon cancer cases in men in Denmark could be reduced by 27% if the incidence for all men was equal to that found for the low risk group of farmers.