OBJECTIVE: To quantify the eventual extra loss of life incurred to cancer patients in Estonia compared with those in Sweden that was possibly attributable to differences in society. DESIGN: Population based survival of cancer patients in Estonia was compared with that of Estonian immigrants to Sweden and that of all cancer patients in Sweden. The cancer sites studied were female breast and ovary, male lung and prostate, and male and female stomach and colon. SETTING: Data on incident cases of cancer were obtained from the population based Swedish and Estonian cancer registries. PARTICIPANTS: Data from Estonian patients in Sweden, Estonian patients in Estonia, and patients from the total Swedish population were included in the study. MAIN RESULTS: Differences in survival among the three populations, controlling for follow-up time and age at diagnosis, were observed in breast, colon, lung, ovarian, and prostate cancers. The survival rates of Estonians living in Sweden and the total population of Sweden were better than that of the Estonians living in Estonia. For cancers of the breast and prostate, the excess mortality in the older age group (75 and above) was much greater in Estonia than in the other populations. CONCLUSIONS: Most differences in cancer survival between Estonian and Swedish populations studied could be attributed to a longer delay in diagnosis, and also to inferior treatment (including access to treatment) in Estonia compared with Sweden. Estonia's lag in socioeconomic development, particularly in its public health organisation and funding, is probably the main source of the differences observed.
Chlorination of water rich in organic material is known to produce a complex mixture of organochlorine compounds, including mutagenic and carcinogenic substances. A historical cohort study of 621,431 persons living in 56 towns in Finland was conducted in order to assess the relation between historical exposure to drinking water mutagenicity and cancer. Exposure to quantity of mutagenicity was calculated on the basis of historical information of raw water quality and water treatment practices using an empirical equation relating mutagenicity and raw water pH, KMnO4 value and chlorine dose. Cancer cases were derived from the population-based Finnish Cancer Registry and follow-up time in the study started in 1970. Age, gender, time period, social class, and urban residence were taken into account in Poisson regression analysis of the observed numbers of cases using expected numbers of cases standardized for age and gender as a basis. Excess risks were calculated using a continuous variable for mutagenicity for 3,000 net rev/l exposure representing an average exposure in a town using chlorinated surface water. After adjustment for confounding, a statistically significant excess risk was observed for women in cancers of the bladder (relative risk [RR] = 1.48, 95 percent confidence interval [CI] = 1.01-2.18), rectum (RR = 1.38, CI = 1.03-1.85), esophagus (RR = 1.90, CI = 1.02-3.52), and breast (RR = 1.11, CI = 1.01-1.22). These results support the magnitude of excess risks for rectal and bladder cancers found in earlier epidemiologic studies on chlorination by-products and give additional information on exposure-response concerning the mutagenic compounds. Nevertheless, due to the public health importance of water chlorination, uncertainty related to the magnitude of observed risks, and the fact that excess risks were observed only for women, the results of the study should be interpreted with caution.
OBJECTIVE: To evaluate, by analysis of breast cancer mortality data from all the 26 Swedish counties for the years 1971 to 1990, whether the effect of the introduction of mammography screening in Sweden can be assessed by observation from existing mortality data. METHODS: A Poisson regression model was used to study whether a decrease in breast cancer mortality among women aged 50-74 years was associated with the extent of mammography screening in different counties and periods. RESULTS: In regions where mammography screening had been introduced, breast cancer mortality tended to be decreased, on average, compared with regions without screening. If a 10 year time lag between the start of screening and its full effect on mortality is assumed then the estimated reduction in breast cancer mortality associated with introduction of screening was 19% with a 95% confidence interval ranging from -3% to 37%. CONCLUSIONS: The results suggest that the effect of mammography screening may be studied using existing routine mortality data and appropriate statistical modelling. This way of assessing the outcome of the screening is valuable when continuously monitoring a screening programme that has become a public health routine.
This case-control study based in Nordic serum banks evaluated the joint effects of infections with genital human papillomavirus (HPV) types, and Chlamydia trachomatis in the aetiology of cervical squamous cell carcinoma. Through a linkage with the cancer registries, 144 cases were identified and 420 controls matched to them. Exposure to past infections was defined by the presence of specific IgG antibodies. The odds ratio (OR) for the second-order interaction of HPV16, HPV6/11 and C. trachomatis was small (1.0) compared to the expected multiplicative OR, 57, and the additive OR, 11. The interactions were not materially different among HPV16 DNA-positive squamous cell carcinomas. When HPV16 was replaced with HPV18/33 in the analysis of second-order interactions with HPV6/11 and C. trachomatis, there was no evidence of interaction, the joint effect being close to the expected additive OR. Possible explanations for the observed antagonism include misclassification, selection bias or a true biological phenomenon with HPV6/11 and C. trachomatis exposures antagonizing the carcinogenic effects of HPV16.
Intracranial meningioma was diagnosed and histologically verified in 1986 patients, 597 men and 1389 women, between 1953 and 1984 in Finland. The closing date of this survival study was December 31, 1987, and the follow-up was complete. Meningiomas, usually slowly growing and surgically curable benign tumors, caused considerable short-term mortality, with a relative survival rate (RSR) of 83% at 1 year, and slight but continual long-term mortality, with RSR of 71% at 15 years. From 1979 to 1984, when computed tomography (CT) was available, the mortality at 3 months for the patients who had surgical procedures was 2% in those younger than 45 years and 10% in those older than 64 years; patients who did not have operations had 1-year mortality of 61%. The short-term and long-term excess mortalities are associated significantly with old age, no surgical procedure, and the period of diagnosis; the long-term excess mortality also is associated with male gender.
Estimation of cancer patient survival by social class has been performed using observed, corrected (cause specific), and relative (with expected survival based on the national population) survival rates. Each of these measures are potentially biased and the optimal method is to calculate relative survival rates using social class specific death rates to estimate expected survival. This study determined the degree to which the choice of survival measure affects the estimation of social class differences in cancer patient survival.
All Finnish residents diagnosed with at least one of 10 common malignant neoplasms during the period 1977-1985 were identified from the Finnish Cancer Registry and followed up for deaths to the end of 1992.
Survival rates were calculated by site, sex, and age at 5, 10, and 15 years subsequent to diagnosis for each of three measures of survival; relative survival, corrected (cause specific) survival, and relative survival adjusted for social class differences in general mortality. Regression models were fitted to each set of rates for the first five years of follow up.
The degree of variation in relative survival resulting from social class decreased, although did not disappear, after controlling for social class differences in general mortality. The results obtained using corrected survival were close to those obtained using relative survival with a social class correction. The differences between the three measures were largest when the proportion of deaths from other causes was large, for example, in cancers with high survival, among older patients, and for longer follow up times.
Although each of the three measures gave comparable results, it is recommended that relative survival rates are used with expected survival adjusted for social class when studying social class variation in cancer patient survival. If this is not an available option, it is recommended that corrected survival rates are used. Relative survival rates without the social class correction overestimate social class differences and should be used with caution.
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The interest in estimating the probability of cure has been increasing in cancer survival analysis as the curability of many cancer diseases is becoming a reality. Mixture survival models provide a way of modelling time to death when cure is possible, simultaneously estimating death hazard of fatal cases and the proportion of cured case. In this paper we propose an application of a parametric mixture model to relative survival rates of colon cancer patients from the Finnish population-based cancer registry, and including major survival determinants as explicative covariates. Disentangling survival into two different components greatly facilitates the analysis and the interpretation of the role of prognostic factors on survival patterns. For example, age plays a different role in determining, from one side, the probability of cure, and, from the other side, the life expectancy of fatal cases. The results support the hypothesis that observed survival trends are really due to a real prognostic gain for more recently diagnosed patients.
Intracranial glioma was diagnosed during the patient's life and histologically verified in 3857 patients between 1953 and 1984 in Finland. Their survival up to the end of 1987 was analyzed, the follow-up being complete. The treatment was by operation in 1193 cases, radiation in 459 cases, both operation and radiation in 1486 cases, and neither operation nor radiation in 719 cases. The 1-year, 5-year, 10-year, and 15-year cumulative relative survival rates were 0.53, 0.29, 0.20, and 0.18, respectively. The newborn to 14-year-olds lost 56% of their life expectancy; the 15-year-olds to 44-year-olds, 71%; the 45-year-olds to 64-year-olds, 88%; and the 65-year-olds to 99-year-olds, 91%. According to the model with the best fit in regression analysis the prognosis was significantly better among young, recently diagnosed patients who had undergone both operation and radiation.
A joint Nordic study was conducted to elucidate the survival pattern in male breast cancer by means of regression analysis of annual relative survival rates. A total of 1429 (98.4%) of all patients diagnosed during a 25-year to 30-year period and reported to the Nordic cancer registries were available for follow-up through 1982. The relative survival rate was lower in older patients; the relative excess risk of dying (from breast cancer) during the first 5 years of observation, calculated by multiple regression modelling, increased in a regular fashion more than three-fold from patients younger than 40 years at diagnosis to those aged 80 years or older. Significantly lower rates were found among males in Denmark and Finland, the relative excess risks of dying (compared with Sweden) being 1.39 (1.06-1.80) and 1.73 (1.22-2.45), respectively, during the first 5 years. The authors concluded first that important differences exist between male and female patients with breast cancer in the relation between survival and age at diagnosis, and secondly that a later stage at presentation or national differences in the natural history are the most likely explanations for the worse prognosis in Denmark and Finland.
A Swedish cohort of 14,351 infants exposed to ionizing radiation for skin hemangioma was analyzed with respect to thyroid cancer risk. The subjects were irradiated during the period 1920-1959 and radiotherapy was given with beta particles, gamma rays and/or X rays. The mean absorbed dose to the thyroid was 0.26 Gy (range