Publications (14)55.33 Total impact
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Article: A case-control study to estimate the impact of the Icelandic population-based mammography screening program on breast cancer death.
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ABSTRACT: The Icelandic breast cancer screening program, initiated November 1987 in Reykjavik and covering the whole country from December 1989, comprises biennial invitation to mammography for women aged 40-69 years old. To estimate the impact of mammography service screening in Iceland on deaths from breast cancer. Cases were deaths from breast cancer from 1990 onwards in women aged 40 and over at diagnosis, during the period November 1987 to December 31, 2002. Age- and screening-area-matched, population-based controls were women who had also been invited to screening but were alive at the time their case died. Using conditional logistic regression on the data from 226 cases and 902 controls, the odds ratio for the risk of death from breast cancer in those attending at least one screen compared to those never screened was 0.59 (95% CI 0.41-0.84). After adjustment for healthy-volunteer bias and screening-opportunity bias, the odds ratio was 0.65 (95% CI 0.39-1.09). These results indicate a 35-40% reduction in breast cancer deaths by attending the Icelandic breast cancer screening program. These results are consistent with the overall evidence from other observational evaluations of mammography-based programs.Acta Radiologica 12/2007; 48(9):948-55. · 1.37 Impact Factor -
Article: The influence of mammographic screening on national trends in breast cancer incidence.
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ABSTRACT: 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.European Journal of Cancer Prevention 05/2005; 14(2):117-28. · 2.13 Impact Factor -
Article: Early life events and later risk of colorectal cancer: age-period-cohort modelling in the Nordic countries and Estonia.
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ABSTRACT: A lowering of colorectal cancer risk for the birth cohorts born around World War II (WWII) has previously been observed in Norway, a country which suffered some 20% caloric restriction during the war. The purpose of the study was to conduct a similar kind of analysis in the other Nordic countries and Estonia, which were also subjected to various degrees of energy restriction during WWII. All new cases of colorectal cancer in the Nordic countries and Estonia diagnosed between 40 and 84 years of age and born between 1874 and 1953, were collected from the national cancer registries. The incidence data were fitted to an age-period-cohort model. A transient drop in the estimated colorectal cancer incidence rate was observed for the birth cohorts born around WWII in Estonia, together with a tendency of decreased risk in Sweden and Denmark. The previously observed lowering of colorectal cancer risk for persons born during WWII in Norway also prevails in Estonia. Energy restriction is a possible explanation for these findings, since the countries suffered from varying nutritional conditions during the war. Exogenous factors acting during periods early in life may have an impact on later colorectal cancer risk.Cancer Causes and Control 05/2005; 16(3):215-23. · 2.88 Impact Factor -
Article: Breastfeeding and reduced risk of breast cancer in an Icelandic cohort study.
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ABSTRACT: Case-control studies on the association between breastfeeding and the subsequent risk of breast cancer have given inconsistent results. To date, only two cohort studies have been reported on this subject. The present nested case-control study uses data from an Icelandic cohort of 80,219 women visiting a Cancer Detection Clinic that offers population-based cervical and breast cancer screening, in the years 1979-1995. The 993 parous cases were aged 26-90 years at diagnosis, with 9,729 parous controls individually matched on birth year, vital status at case diagnosis, and age when giving information on several potential risk factors for breast cancer. Using conditional logistic regression and confining the analysis to the 84 cases who were <40 years at diagnosis, an inverse association was evident between total duration of breastfeeding and breast cancer, with the adjusted odds ratio = 0.77 per 6 months' increase in duration of breastfeeding (95% confidence interval: 0.59, 1.00), whereas for the remainder of the women, a much weaker trend was observed. Ever lactating was associated with decreased risk, with the adjusted odds ratio = 0.33 (95% confidence interval: 0.19, 0.56) for women diagnosed at all ages. This is the first cohort study to indicate a negative association between breastfeeding and breast cancer.American Journal of Epidemiology 07/2001; 154(1):37-42. · 5.22 Impact Factor -
Article: Altered expression of HLA class I antigens in breast cancer: association with prognosis.
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ABSTRACT: Loss of surface expression of class I major histocompatibility antigens is commonly observed in malignant tumors and has been considered one of the mechanisms for escape from cytotoxic T cells. However, natural killer cells kill cells lacking HLA class I antigens. In the present study, we characterized by immunohistochemistry the HLA class I expression of breast carcinomas from 187 patients with TNM stages I and II, diagnosed 1981-1984, using beta(2)-microglobulin as a marker and evaluated the effect on survival with a follow-up of up to 14 years. The largest group (48%) consisted of HLA class I-negative tumors (< or =10% of cells stained), mixed expression (>10% and <80% of cells stained) was seen in 36% and only 15% were classified as HLA class I-positive (> or=80% cells stained). No associations could be established with various clinicopathological parameters, such as tumor size, presence of lymph node metastases, histological grade, expression of hormone receptors, S phase and p53 mutations. There was no effect on recurrence-free survival in the whole group; but among node-negative patients (n = 86), those who had tumors with mixed HLA class I expression had a significantly higher probability of disease recurrence (OR = 3.42, p = 0.014) than patients with either HLA class I-positive or -negative tumors, particularly after more than 5 years. In node-positive patients who received adjuvant therapy, this phenotype was not associated with disease recurrence.International Journal of Cancer 12/2000; 89(6):500-5. · 5.44 Impact Factor -
Article: Altered expression of E-cadherin in breast cancer. patterns, mechanisms and clinical significance.
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ABSTRACT: Reduced cell adhesion brought about by altered surface expression of E-cadherin has been implicated in invasive and metastatic malignant growth. We investigated the patterns of immunohistochemical E-cadherin expression in 120 breast carcinomas. Furthermore, we analysed DNA from the same samples for loss of heterozygosity (LOH) using three separate microsatellite markers on chromosome 16q22.1. Finally, the clinical outcome was ascertained for 108 patients. 19% (18/97) of infiltrating ductal carcinomas showed complete loss of E-cadherin expression compared with 64% (9/14) of infiltrating lobular carcinomas. LOH was detected in 46% (24/52) of infiltrating ductal carcinomas and 89% (8/9) of infiltrating lobular carcinomas. In the infiltrating lobular carcinomas, LOH was associated with complete loss of cell membrane expression of E-cadherin, although a cytoplasmic expression pattern was evident. In contrast, this association was not seen in the infiltrating ductal carcinomas. In a multivariate analysis, loss of E-cadherin expression was shown to be a significant independent risk factor for a poorer disease-free survival (P=0.019), in particular in the node-negative subset of patients (P=0.029). Significance was also approached for breast cancer corrected survival (P=0.056). We conclude that different mechanisms are involved in the altered E-cadherin expression seen in different subtypes of breast carcinomas. Furthermore, we implicate loss of E-cadherin, regardless of the genetic causes, as an independent prognostic marker for disease recurrence, especially in node-negative breast cancer patients, irrespective of the histological type.European Journal of Cancer 07/2000; 36(9):1098-106. · 5.54 Impact Factor -
Article: Genetic epidemiology of breast cancer: segregation analysis of 389 Icelandic pedigrees.
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ABSTRACT: A genetic epidemiologic investigation of breast cancer involving 389 breast cancer pedigrees including information on 14,721 individuals from the Icelandic population-based cancer registry is presented. Probands were women born in or after 1920 and reported to have breast cancer in the cancer registry. The average age of the 389 probands was 45.5 years (SD 8.92). Segregation analyses was performed evaluating residual maternal effects, a dichotomous cohort effect, and assuming the age at diagnosis followed a logistic distribution after log-transformation. Familial aggregation could be best explained by the inheritance of a high-risk allele leading to early onset breast cancer among the homozygotes, which represent approximately 2.6% of the population. A Mendelian codominant model was selected as the best fitting model, with an estimated age at diagnosis of 51.8 years among these high-risk homozygotes, 64.0 years for heterozygotes and 76.3 years for the low-risk genotype. The predicted cumulative risk for homozygote carriers of the high-risk allele is 32.2% by age 60, compared to 16.4% for heterozygotes and 5.0% for non-carriers of the same age. These predicted age profiles in the current study complement recent reports from Iceland of a majority of BRCA2 mutation carriers being diagnosed with breast cancer below the age of 50 years, and 60 years being the mean age at diagnosis for non-carriers. This model also predicted a high background risk of breast cancer for women in this population (estimated susceptibility gamma = 0.44 +/- 0.08). This implies that if carriers and non-carriers did not die of competing causes, the estimated risk of being diagnosed with breast cancer by age 80 years irrespective of carrier status is 11.4%.Genetic Epidemiology 02/2000; 18(1):81-94. · 3.44 Impact Factor -
Article: Breast cancer incidence and familiality in Iceland during 75 years from 1921 to 1995.
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ABSTRACT: Information in the Icelandic Cancer Registry on breast cancer and its collection of breast cancer families has been used to elucidate changes in breast cancer incidence by time period and by age, and the effect of degree of relationship and age on the familial risk of breast cancer. Since 1921 the incidence rates have increased, but the increase is significantly greater (2.06% per year) for ages over 44 years than for ages 20-44 (1.20% per year). It has been shown before that when familial risk is computed, the age of the proband influences the risk for the relatives. However, this study shows that the age of the relative is also important and with increasing age the familial risk decreases.Journal of Medical Genetics 03/1999; 36(2):103-7. · 6.36 Impact Factor -
Article: Risk factors for malignant diseases: a cohort study on a population of 22,946 Icelanders.
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ABSTRACT: The records of a cohort of 11,580 females and 11,366 males participating in an Icelandic cardiovascular risk factor study were linked with the Icelandic Cancer Registry, identifying 1,785 males and 1,490 females who had been registered with neoplastic diseases from 1968 to 1995. The interval between the time of measurement of the variables and the diagnosis of the malignancy ranged from 4 to 27 years. The variables consisted of answers from a questionnaire on smoking and the use of hypertensive drugs and anthropometric and biochemical measurements. Cox's regression was applied to analyze the predictive power of the variables on the risk of cancer after the first examination at the Heart Preventive Clinic, Reykjavík. Univariate analyses, adjusted for age, were performed for each variable and each major site. Within each major site, multivariate regression analysis was applied for variables that were found significantly (10% level in univariate analysis) positive or negative as risk factors. The results show that smoking is the most important risk factor, negative only for endometrium. For lung cancer, the risk is twice as strong for females as it is for males, whereas for pancreas, males have a relative risk ratio of 4.5, compared with 2.4 for females. Height is a risk factor for all sites for each sex, for breast in females, and for kidney in males. Several anthropometric risk factors were studied. Some of these can describe positive or negative relative risk ratios for cancer, and their use may shed light on cancer pathogenesis. Serum cholesterol is a negative risk factor for breast cancer in females, but triglycerides are a positive risk factor for cervix cancer in females and for colon or rectum and thyroid cancer in males. Serum glucose is a positive risk factor for prostate cancer and a negative risk factor for lymphomas and leukemias.Cancer Epidemiology Biomarkers & Prevention 12/1997; 6(11):863-73. · 4.12 Impact Factor -
Article: Oral contraceptive use at a young age and the risk of breast cancer: an Icelandic, population-based cohort study of the effect of birth year.
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ABSTRACT: The possible association between breast cancer and oral contraceptive use before the age of 20 was investigated using Icelandic population-based information from women born after 1944. The design was a nested case-control study within a cohort, using data on duration of oral contraceptive use at young ages. The availability of oral contraceptives before the age of 20 has changed dramatically and is highly dependent on birth years, with 20% and 82% starting before the age of 20 among Icelandic users born in 1945-47 and 1963-67 respectively. The association between total duration of oral contraceptive use and breast cancer was significantly dependent on year of birth. In women born in 1951-67 (based on 81 cases), the relative risk (RR) associated with use for more than 4 years was 2.0 (95% CI 1.1-3.7). The association disappeared when women born in 1945-50 were included (RR 1.1,95% CI 0.8-1.6), adding 123 cases. A significant trend of increased risk with longer duration was present only in the group born after 1950, with RR 0.9, 1.7 and 3.0 for < or = 4 years, >4-8 years and > 8 years of use respectively. The results of this study indicate an association between breast cancer and oral contraceptive use at a young age. They also stress the importance of distinguishing between groups with different opportunities for exposure at young age.British Journal of Cancer 01/1997; 75(1):139-43. · 5.04 Impact Factor -
Article: Epidemiology of breast cancer in families in Iceland.
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ABSTRACT: The Icelandic Cancer Registry has collected 989 pedigrees of breast cancer patients since 1972. In addition to the probands, the families also include 401 other women with breast cancer, so family information exists for 1390 women with breast cancer out of a total of 2748 diagnosed with the disease from 1910 to 1988. Most of the probands have been selected with care to avoid the bias of selecting families with a known history of breast cancer. After excluding all those who did not conform to the strict selection criteria, 947 pedigrees remained for this analysis. First, second, and third degree relatives all had a significantly increased risk of breast cancer: 2.26, 1.43, and 1.49, respectively. Male relatives also had a significantly increased risk, whereas females related by marriage had not. Of the first degree relatives, sisters had the largest increase in risk. When pedigrees were classified by the age at diagnosis of breast cancer of the proband, the risk was highest in the relatives of probands who were young at diagnosis. Bilaterality of breast cancer increased the risk in relatives and the highest risk (9.04) was found in sisters of probands with bilateral disease and an age at diagnosis of first cancer of less than 45 years (95% confidence limits 4.14, 17.18). Sisters consistently have the highest risk, significantly higher than other first degree relatives. This points to an important role of shared environmental aetiological factors acting after birth and it can not yet be excluded that most of the increase in risk can be explained by this.(ABSTRACT TRUNCATED AT 250 WORDS)Journal of Medical Genetics 04/1992; 29(3):158-64. · 6.36 Impact Factor -
Article: Reproductive factors and breast cancer risk in Iceland. A second cohort study.
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ABSTRACT: In a previous prospective study we showed elevated risks for breast cancer in nulliparous women compared to parous women, in those having their first pregnancy at a higher age, and those with few children. This was based on 216 women diagnosed with breast cancer during 1965 to 1975 among 34,525 women having attended the cervix cancer detection clinic in Iceland by the end of 1974, and born between 1906 and 1945. The present investigation on 848 cases, diagnosed among 61,040 women attending the cervix cancer detection clinic during 1964 to 1984 and born between 1901 and 1960, shows the same risk factors to be significant. The relative risks are, however, smaller. The reasons for the difference in relative risks are discussed. We find that the effect of age at first birth is significant for women up to the age of 65 and not for older women. In both cohorts, women older than 55 are underrepresented and more so in the earlier report. In addition, the small number of cases in the reference group with age at first birth below 20 appears to have made the figures of our earlier report unreliable.International Journal of Cancer 01/1991; 46(6):972-5. · 5.44 Impact Factor -
Article: A decline and a halt in mean age at menarche in Iceland.
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ABSTRACT: Mean age at menarche has been declining in many countries during the past hundred years. Reports of a halt in this trend have come from Oslo and London. In this study the trend in age at menarche in successive birth cohorts, starting in 1900, was investigated for the first time in Iceland. This was based on recall data obtained as part of a cervical cancer screening programme covering the whole country. Around 78% of the female population at the ages targeted for screening responded to questions on reproductive factors in the years 1964-89, or over 73,000 women aged 20-69 years. Investigation of the validity and reliability indicated that the estimated mean age is likely to be unbiased, and that for 90% of the women the information was reliable. Mean age at menarche declined from 14.9 years to 13.5 years in successive cohorts of Icelandic women born 1900 to around 1950. In cohorts born 1951-67 the mean age has remained stable. The halt appeared later than reported from Oslo and London and at a higher age.Annals of Human Biology 21(2):179-86. · 1.98 Impact Factor -
Article: Oral contraceptive (OC) use and risk of breast cancer - reply
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1997
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University of Iceland
- Faculty of Medicine
Reykjavík, Capital Region, Iceland
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