Document 2j5yVLm4qJ8RGOjm9d4BqqMrR

Bladder Cancer in Estonia, 1968-1992: Incidence, Mortality, Prevalence and Survival Gennadi Timberg,' Mati Rahu,2 Kaja Gornoi,* Tiiu Aareleicf and Alex Baburin2 From the 'University Hospital, University of Tartu, T a m , Estonia and 2Department of Epidemiology and Biostatistics, institute of Experimental and Clinical Medicine, Tallinn, Estonia (Submitted August 5, 1996. Accepted for publication November 4, 1996) Scand J Urol Nephrol 31: 337-342, 1997 This paper summarizes what is known about the occurrence and survival of bladder cancer in Estonia from 1968 to 1992.In 1988-92 the age standardized (world standard)incidence rate of bladder cancer was 11.1 per 100,OOO person-years in males and 2.0 in females, and the age standardized mortality rate was 8.2 and 2.7, respectively;by July 1, 1990 the age standardized prevalence rate was 41.5 and 14.7, respectively. Between 1968-72 and 1988-92, incidence increased by 1.26 times (95% confidence interval 1.09 to 1.46) among males; incidence rates for females did not show a consistent trend. The time trends in mortality generally paralleled the trends in incidence. Higher rates of bladder cancer were found among males in five large towns. For patients diagnosed in 1983-87,the five-year relative survival was 32.4%(95%confidence interval 27.0 to 37.8) for males and 32.5%(23.8 to 41.2) for females; throughoutthe 20 years there was no improvement in survival. As the survival rates are less favorable than those in the Nordic countries, further hospital-based studies are needed to investigate the relation between survival and clinical characteristics: Key words: bladder cancer, incidence, mortality, prevalence, survival, time trend, Estonia. +G e n d i Timberg, University Hospital, University of Tartu, L. Puusepa 8, EE2400 Tartu, Estonia. Tel: 372 7 448 250. Fax: f 372 7 448 106) As a result of political and economical changes since (ECR), which is population based and covers the whole 1991, it has been possible to start and develop of Estonia (area 45,216 km2,population 1.6 million in collaborative research projects in cancer epidemiology 1992).The registry was founded in 1978, but its data is between the Baltic countries and other temtories, retrospective to 1968 (22). particularly the Nordic countries (1,2,19). In this Although mortality statistics is the responsibility of situation, quite often neither the involved nor the the Estonian State Statistical Office, due to limitations potential researchers have basic background informa- in tabulated site coverage and procedures of manual tion on the occurrence of cancer of separate sites analysis in the earlier period (16), for the purposes of among the population from the Baltic countries. Lack the present project mortality data were derived from the of adequate information has hampered joint initiatives ECR. The underlying cause of death in the records of and, presumably, has discouraged to take a next step the ECR is usually the one on the death certificate, from an embryonic stage of collaboration. Up to now, resulting in the record linkage between the ECR's files very limited data has been published on the patterns of and the certificates. As in Estonia cancer patients are urinary bladder cancer in Estonia, although this cancer followed up until death or emigration, data on site among males is frequent (23). At the same time, prevalence and survival are available, too. taking advantage of the long-term cancer registration in The estimates of the resident population of Estonia Estonia (22) it is reasonable to summarize the data for from 1968 to 1992 were derived from the diskettes 25 years and characterize the bladder cancer patterns in accompanying the corresponding monographs (5,6). this area as one of the Baltic countries. The purpose of At the Department of Epidemiology and Biostatis- this study is to present descriptive data for bladder tics, Institute of Experimental and Clinical Medicine, cancer occurrence in Estonia between 1968-92. incidence, mortality, prevalence and survival rates were calculated. Standardization by age was carried MATERIAL AND METHODS out for incidence, mortality and prevalence rates on the basis of the world population (20). Standardization was The data on incident cases and deaths from 1968 to applied to all ages together and for the age group 35- 1992 were obtained from the Estonian Cancer Registry 64. To show the change over time age-standardized I 01997 Scandinavian University Press. ISSN 0036-5599 Scand J Urol Nephrol31 338 G. Timberg et al. Table I. Incidence and rnortaliryfor bladder cancer in Estonia, 1968-92,males and females I Period 1988-92l1968-72 Incidence/mortality measures Sex 1968-72 1973-77 1978-82 1983-87 1988-92 rate ratio (95% CI)a I Averme number of cases per year M 59 55 67 91 95 F 26 21 24 34 36 I Incidence rate per 1OO,O0Operson-years M F 9.5 3.5 8.3 12.8 12.8 13.0 1.37 2.7 3.0 4.2 4.3 1.23 Age-standardizedincidence rate per 100,000 person-yearsb all ages 35-64 years M 8.8 F 2.0 ~~ M 10.8 F 2.5 7.5 11.4 11.4 11.1 1.26 (1.09-1.46) 1.4 1.5 2.0 2.0 1.04 (0.82-1.33) 9.8 12.2 14.3 15.5 1.44 (1.34-1.54) 1.8 1.9 1.7 2.2 0.89 (0.77-1.02) Average number of deaths per year M 40 39 43 64 60 F 21 17 17 23 23 Mortality rate per lOO,OoO person-years M 6.5 6.0 6.3 8.9 8.2 1.26 F 2.8 2.2 2.1 2.8 2.1 0.96 Age-standardizedmortality rate per 100,000 person-yearsb all ages M 6.0 5.2 5.5 8.0 7.0 1.18 (0.99-1.42) F 1.4 1.o 1.o 1.2 1.3 0.88 (0.66-1.17) 35-64 years M 5.3 4.5 5.5 7.2 8.1 1.53 (1.36-1.72) F 1.2 1.o 0.8 0.8 1.o 0.81 (0.63-1.04) a Rate ratios are calculated on the basis of unrounded rates. World population was used as standard. ASIWASMR per 100,000 person-years 3100 loo males 10 / - females incidence -: -incidence 10 1 rl 0.1 1968 i"'l"'i"'l"'l"'- 1972 1976 1980 1984 1988 Year of diagnosis 0.1 1992 Fig. I. Time trends in agestandardized incidence (ASIR, world population) and mortality rates (ASMR, world population) for bladder cancer in Estonia, 1968-92, males and females. Rates are presented as three-year moving averages. incidence rate (ASIR) ratios and age-standardized mortality rate (ASMR) ratios were calculated as the 1987-92/1968-72 ratio. The 95% confidence interval (CI) for the rate ratios were calculated as described by Boyle and Parkin (4). To examine the regional differences in bladder cancer incidence, age-standardized rates for 15 counties and 5 large towns were calculated for the period 1968-92; the region / whole Estonia ratios of the ASIR's and related 95% con- fidence limits were found and visualized on the Figures. After having excluded 95 cases of bladder cancer, diagnosed after death, the basic material for survival analysis consisted of 1793 cases (1289 males and 504 females), i.e., 95% of the total of 1888,diagnosed from 1968 to 1987. Of these, 9 males (0.7%) and 6 females (1.2%) were lost to follow up, mainly as a result of patient emigration. For these patients, the date of the S c a d J Urol Nephrol31 Incidence rate per 100,000 person-years 140 ,- 140 males 0 . I r I r I I/ / , 0- 10- 20- 30- 40- 50- 60- Age at diagnosis * 1.0 70- 80- Fig. 2. Age-specific incidence rates for bladder cancer in Estonia, 1988-92, males and females. last contact was used as the end of follow-up. For other patients, the closing date was December 31, 1992. To analyze survival of bladder cancer patients observed and relative survival rates were calculated. The relative survival rate is the ratio of the observed and the expected survival rates; the latter was calculated from the population life tables for Estonia, provided by the Estonian State Statistical Office. Expected survival probabilities were calculated using the method of Hakulinen (9). The survival analysis was performed with the pertinent computer program (10). RESULTS Incidence 2541 new cases of bladder cancer were registered in Estonia during the period 1968-92, and 1834 of them among males and 707 among females. In 1988-92, the proportion of bladder cancers among all incident cases of cancer (including skin cancers) was 3.8% for males and 1.4% for females. Crude incidence rates show an increase from 1968-72 to 1988-92 for both sexes (Table I). The age-standardized incidence rates are generally increasing for males (Fig. l), and have been relatively stable for females. The highest incidence rates have been observed for males (130 per 100000) and females (34 per 100OOO) in the age group 75-79 years (Fig. 2). The trend for the age group 35-64 years 0.2 0.6 1.o 1.4 Tartu Tallinr Narva 3VbrUmaa Piimu Kohtla-JWe Viljandimaa JWamaa Harjumaa Pblvamaa Jbgevamaa valgamaa I Ida-Vim Hiiumaa -I I Lilgne-Vi PgmUmaa Raplamaa TaltUIlaa Saaremaa memaa 0.2 0.6 1.o 1.4 Rate ratio Fig. 3. Rate ratio of age-standardized incidence (ASIR, world population) and 95% confidence interval for bladder cancer in the counties and large towns in Estonia, 1968-92, males. (ASIR for the whole of Estonia is equal to 1.) shows a 44% increase for males and a small decrease for females. For males, age-standardized rates are more than five times higher than those for females. Due to a small number of cases it is complicated to interpret geographical distribution of bladder cancer in Estonia (Fig. 3 and 4). However, regional differences reveal that men living in large towns (Tallinn, Tartu, Narva, Kohtla-JWe and P h u ) are more affected than those in rural areas. Among women, urban predominance cannot be observed. Mortality On the whole, 1730 deaths from bladder cancer were registered during the period 1968-92, of whom 1230 were males and 500 females. Cancer of urinary bladder caused 3.4% of all cancer-related deaths in males and 1.6% in females in 1988-92. Age-standardized mortality rates increased for males and slightly decreased for females, this trend is similar and even more pronounced for the age group 35-64 years (Table 1 and Fig. 1). For males, in recent decades, mortality rates are about three times higher than those for females. S c a d J Urol Nephrol31 I 340 G. Timberg et al. 0.2 0.6 1.0 1.4 1.8 2.2 2.6 3.0 Liiiinemaa valgamaa Tartu Tallinn PiirnU Likle-Viaa Vbrumaa Kohtla-JHNe Viljandimaa Tarturnaa Jbgevamaa Harjumaa Saaremaa JiirVamaa Narva PhUl3llIa Hiiumaa Pblvamaa Ida-Viaa Raplamaa 0.2 0.6 1.0 1.4 1.8 2.2 2.6 3.0 Rate ratio Fig. 4. Rate ratio of age-standardized incidence (ASIR, world population) and 95% confidence interval for bladder cancer in the counties and large towns in Estonia, 1968-92, females. (ASIR for the whole of Estonia is equal to 1.) Prevalence By July 1, 1990 there were 428 prevalent cases (305 in males and 123 in females) of bladder cancer in Estonia. Among all prevalent cases of cancer (including skin cancer), bladder cancer occupied 3.9% in males and 0.7% in females. The crude prevalence rate (per 100000) was 41.5 among males and 14.7 among females. The age standardized rate for all ages was 36.4 among males and 7.8 among females, and for the 35-64 age group, 48.7 and 7.3, respectively. Survival Fig. 5 shows relative survival rates (RSR) for bladder cancer diagnosed between 1983-87. The survival curves in both sexes are very close to each other. The one-year and the five-year relative survival rate among the males was 60.0% and 32.4%, respectively, and among females 58.6% and 32.5%, respectively. Throughout the twenty years (1968-87) studied there was no evidence of improvement in the five-year observed and relative survival (Table 11). The survival rates by age groups over time are not prepented because of the small number of cases, causing substantial fluctuation of the rates. DISCUSSION In Estonia in the period 1988-92, incident cases of cancer of the urinary bladder ranked eighth among males and fifteenth among females (27). Comparison of the age-standardized incidence rates for 1983-87 reveals (20,23) that among the Nordic and the Baltic countries, the level of incidence is quite close in Finland, Estonia, Latvia and Lithuania, but it is much higher in Denmark, Norway, Iceland and Sweden. These large discrepancies are known and they reflect, first of all, different practices of recording papillomas (20). Certainly, the general quality of cancer registration may affect bladder cancer incidence rates in Estonia considerably. Thus, the percentage of microscopical confirmation of bladder cancers in 1988-92 was 80 among males and 72 among females (27), which is approximately 15-20% less than that in the Nordic countries (20). These differences in microscopical confirmation are more pronounced in older age groups which suggests that a sharp decrease in age-specific rates in the ages over 75 years may be due to some underdiagnosis or/and underregistration of bladder cancers in Estonia. Although the completeness of cancer registration in Estonia is estimated to be 9598% (2), no special studies have been conducted to substantiatethis percentage. Clearly, further studies are needed to estimate the completeness and accuracy of bladder cancer registration in Estonia. Internationally, between the early 1960s and mid 1980s, a rise in bladder cancer incidence took place in most countries (18). In Estonia, the increase occurred only in males. It implies also that a trend towards increasing male/female ratio was observed in Estonia. The trends in mortality generally paralleled the trends in incidence. High rates of bladder cancer incidence were seen among males in five large towns of Estonia. Bladder cancer has been frequently associated with cigarette smoking and occupational chemical carcinogens (17,24). A total of about 50% of bladder cancers in males are estimated to be related to smoking (1l), and 21-25% to occupational exposures (25). Elevated bladder cancer incidence for males in large towns of Estonia argue in favor of these factors. However, observed geographical differences must be interpreted cautiously because of small numbers. For this analysis, we have used official data on cancer deaths obtained from the central statistical office and transferred to the database of the cancer registry. It is difficult to imagine how valid are official mortality rates for bladder cancer in Estonia, but for the purpose of our current investigation they are enough relevant. Generally, limitations in routinely available Scand J Urol Nephrol SI ,~ I 1 I Bladder cancer occurrence in Estonia 341 Table 11. Five-year observed and relative survival rates for bladder cancer in Estonia, 1968-87, males and j e m l e s ~ ~Five-year survival rate (YO) Year of diagnosis Sex No. of casesa Observed Relative 95% CIb 1968-72 1973-77 1978-82 1983-87 M 280 24.1 30.3 23.9-36.8 F 123 24.6 28.9 19.7-38.0 M 261 25.0 32.2 25.3-39.2 F 99 17.7 21.4 12.0-30.7 M 317 21.9 28.1 22.1-34.1 F 114 22.3 27.1 17.6-36.7 M 43 1 25.3 32.4 27.0-37.8 F 168 25 .O 32.5 23.8-41.2 a Number of cases included in survival analysis. Confidence interval of relative survival rate. Relative survival rate (%) 100 -q 90 80 70 60 50 40 30 20 , 100 90 80 70 60 50 40 30 20 0 0l o 0 12 34 5 6 78 9 Years since diagnosis Fig. 5. Relative survival for bladder cancer in Estonia, 1983-87, males and females. mortality statistics are well known and have been frequently discussed (8,12, 15,21), and death certificate data are used extensively for many epidemiological studies. In countries, where all the population is not covered by cancer registration, mortality rates have been even used to estimate national incidence rates (13). In Estonia, future studies of the quality and reliability of death certification appear highly required if we want to learn more about interpretation of national and international mortality patterns. Survival rates for bladder cancer in Estonia are less favorable than those in the Nordic countries like, e.g., Finland (3) and Sweden (26). Lower survival rates for several other cancer sites in Estonia were found in international comparisons, and they could be explained by delay in diagnosis, lower quality of and somewhat restricted access to surgery (7, 14) and/or selective reporting of more malignant tumors. Our descriptive study does not permit direct conclusions regarding the variety of factors affecting bladder cancer survival in Estonia. Further hospital-based studies are needed to investigate the relation between patients' survival and clinical characteristics with special attention to stage of disease, histological type and grade. One reason for this study was the apparent lack of data on bladder cancer occurrence in Estonia that is available to international readership. The authors hope that the present report will be used as reference material for clinicians, epidemiologists and public health managers involved in national and international projects, particularly in the Baltic and Nordic countries. S c a d J Urol Nephrol31 342 G.Timberg et al. REFERENCES 1. Aareleid T, Pukkala E, Thomson H, Hakama M. Cervical cancer incidence and mortality trends in Finland and Estonia: A screened vs. an unscreened population. Eur J Cancer 1993; 29A: 745-749. 2. Adami HO, Bergstrom R, Mohner M, Zatonski W, Storm H et al. Testicular cancer in nine northern European countries. Int J Cancer 1994; 59: 33-38. 3. 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