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Effect of population screening for carcinoma of the uterine cervix in Finland
Maturrtas. 7 (1985) 3-10 Elsevier
MAT 00345
Effect of population screening for carcinoma of the uterine cervix in Finland M. Hakama Finnish Cancer Registry and University of Tampere, Finland (Received
26 December
1984: accepted
24 January
1985)
The organization of a nationwide population-based screening programme for cervical cancer in Finland is described. The annual incidence of invasive cervical cancer decreased from about 14 to 6 cases per 100,000 during the implementation of the programme. The time trends, age specificity and comparisons with other countries support the conclusion that the organized screening programme was effective in reducing the risk. However, there is no convincing evidence in support of expanding the overall programme to cover a wider age span than 30 to 60 yr or of screening the individual woman more frequently than once every 5 yr, even though these are the current recommendations.
(Key words:
Cancer
of cervix uteri, Population
screening,
Evaluation
of screening
programme)
Introduction Screening for cancer is aimed at detecting preclinical cases of cancer, the objective being to reduce the mortality rate. Cervical cancer has a detectable preinvasive stage and cervical screening therefore aims alternatively at reducing invasive disease. Because total eradication is an impracticable goal and only reduction of the risk is a realistic objective, a balance must be found between the yield and the cost of any screening programme. The yield is the proportion of cases detected by screening out of all the cases diagnosed in the target population. This proportion is related to the reduction in the risk of cervical cancer in the population. One indicator of the cost is the number of women who decide to participate in the programme. The overall cost is directly related not only to the financial cost but also to the possible adverse effects of screening, the latter being a cost factor that is often difficult to assess accurately. The yield and the cost are inversely related and the optimum should be decided upon in advance for any screening programme. There is no scientific method for finding the right balance, since any screening activity is either explicitly or at times
Correspondence to: M. Hakama, SF-33101 Tampere 10, Finland
0378-5122/85/.$03.30
University
of Tampere,
0 1985 Elsevier Science Publishers
Department
B.V.
of Public
Health,
P.O. Box 607.
implicitly based on a series of subjective judgements. The purpose of this paper is to describe how cervical screening is organized in Finland and to relate this to the observed changes in the incidence. In other words, the yield and cost of cervical screening in Finland and the relationship between these factors will be described.
Organizationof the programme
Mass screening was started by the Cancer Society of Finland in the early 1960s. A permanent programme was introduced under which the Finnish female population in the high-risk age groups for cervical cancer is screened every 5 yr. The individual municipalities are responsible for health care in Finland, but the cost is subsidized by the government. The municipalities consequently decide the extent to which women are screened, i.e. the specific cohorts to be screened. The Cancer Society of Finland originally recommended that the 1-yr cohorts aged 40,45 and 50 yr be screened. From the outset, however, there were some deviations from the recommended ages and some variation between the municipalities. In recent years it has been common to have the first screening at age 30 and to continue up to the age of 55. Women eligible for screening are selected by computer from the national population registry. A letter of invitation, with information on the place and time of the screening, is mailed to those selected to participate in the programme. Smears are taken as a rule at local maternity centres by public health nurses or midwives. A notification card is completed with a set of anamnestic data in an interview at the time the smear is taken. The smears are analyzed at the cytological laboratories of the Finnish Cancer Society and all the women participating are notified of the results. Women with malignant or suspected lesions are urged to have further examinations carried out at a specified hospital, which is responsible for reporting diagnostic confirmations together with details of any treatment to the laboratory concerned. The laboratories send full details to the national mass screening registry, which operates within the Finnish Cancer Registry, where the data are linked with the original population data and with any record of previous screenings. The national population registry data, the reports to the Finnish Cancer Registry on all cervical cancer cases diagnosed in the country and the reports on mass screening form the basis for the close surveillance that is maintained of trends in the risk of contracting cervical cancer. The number of annual smears taken under the organized screening programme gradually increased from 2000 in 1963 to roughly 120,000 by 1980, which is equal to about five 1-yr birth cohorts. In addition to those handled under organized screening programme, cytological smears are also commonly taken in general gynaecological practice. The organ&d mass screening smears comprise only one-third to one-fourth of all smears taken in Finland [l]. No exact figures on the overall number of smears are available.
5
Research to predict the ultimate reduction in risk
The risk of cervical cancer before screening, the risk among attenders after the first smear, the risk among non-attenders and the participation rate are all determinants of the ultimate reduction in risk achieved by a screening programme. The registration of the mass screenings, linked with the information obtained from the national population registry and the Finnish Cancer Registry provided the data necessary to predict the effect of screening on the risk at the population level. The first organized screening programmes in the early 1960s resulted in a relatively high rate of attendance - about 80% [l]. There has since been an increase in the rate of non-response, but the rate of attendance is still between 70 and 80%. It is well known that the non-response rate is often affected by self selection resulting in non-participation by the high-risk woman. In Finland no overrepresentation of the high-risk indicators of cervical cancer was found among non-attenders [2]. The women who attended were neither of high social status nor younger than average. Common reasons for non-attendance were recent removal from the municipality resulting in an incorrect mailing address in the national population registry or a recent smear carried out by a private gynaecologist or elsewhere. Only about one-third of those not attending had an unacceptable reason for failing to participate [3]. It was possible to make a direct estimation of the risk of cervical cancer among non-responders by linking up data from the register of invitations, the register of responders and the Finnish Cancer Registry (41. It turned out that while no obvious risk factors characterized those who failed to respond, their cervical cancer risk was 1.7 times that among the overall population before the time of screening or among those not covered by the programme. The estimates of the ultimate reduction in the incidence of cervical cancer assume follow-up after the first screening. On the basis of the first 70,000 women attending for the second time it was found that among those participating the risk of frankly invasive cervical cancer was about 20% of that among those not covered by the programme. When all these results were combined it was predicted that at the population level an approximately 60% reduction in the incidence of frankly invasive cancer should be achieved [4] after the programme had had its full impact. During later years it was possible to assess the accuracy of this prediction.
Effect of the programme at the population level
The simplest indicator of the effect of the programme at population level is the number of cervical cancer cases. Before intensive screening began about 400 new cases of invasive cervical cancer were diagnosed annually. In 1980 there were only 181 new cases of cervical cancer (Fig. l), representing a substantial fall which corresponds roughly to the 60% reduction in the risk that was predicted. The changes in the incidence of cervical cancer correlate with the intensity of the
6 CERVIX
No.ofCases
UTERI
500 1
,,,,,,,.,,,,.,,,
)
855
1960
1965
1970
1915
19Ei
FINNISH CANCER REGISTRY
Fig. 1. Annual number of cases of invasive cervical cancer and in situ lesions in Finland in 1953-1980.
screening programme by age. Fig. 2 shows the age-specific incidence rates in the age groups spanning the 30 to 54 age band. Up to the age of 50 yr, the reduction in the age-specific incidence over the period from the 1950s to the 1970s was 70% or more.
Per IO5
INVASIVE CARCINOHAOFCERVIX
UTERI
50.
co30 -
20 -
10 as43. 2,
Fig. 2. Trends in the age-specific incidence of cervical cancer in Finland for age yr.
groups30-34 to 50-54
Per 10'
INVASIVE CARCINOMA OF CERVIX
Fig. 3. Trends in the age-specific
UTERI
incidence of cervical cancer in Finland for age groups 55-59
to 65-69
v.
The most substantial reduction occurred between 1967 and 1974. Outside that period the changes were smaller and less regular. The changes in the incidence of cervical cancer at age 60 and over were relatively small (Fig. 3). The rates by birth cohort (Fig. 4) confirm the decrease and indicate an abrupt time effect on the rates, which fit well with the intensity of screening. Fig. 5 shows the overall trends in the incidence of cervical cancer and the resultant mortality as well as the trend for carcinoma in situ lesions. There were some discrepancies between the official death certificate diagnoses and information derived from the cancer registry, especially in the early years. The official mortality rates were therefore corrected in accordance with the cancer registry data for the 1950s and 1960s. The total overall age-adjusted incidence was about 14 per 100,000 before the period of intensive screening and by 1980 this rate had fallen to 5.
Alternative programmes
There can be little doubt as to the overall efficacy of screening for cervical cancer. However, no reliable evidence is available in regard to several important aspects of such a programme. The recommendations vary, for example, as to the ages to be covered by screening and to its frequency. Several reports have pointed out an increase in the frequency of cervical lesions among young women. In particular, there has been an increase in the incidence of carcinoma in situ lesions and severe dysplasias. In Finland the rates for invasive
8
FINLAND
J
20
30
40
50
60
70
80
AGE
Fig. 4. Age-specific incidence of cervical cancer in Finland by selected birth cohorts. The dates refer to mid-year of birth for a S-yr age- and time-specific rate. Per 10' 16
CERVIX
UTERI Invasive:incidence
14
6
2 0 FINNISH CANCER REGISTRY
0
Fig. 5. Annual age-adjusted incidence and mortality rates of invasive cervical cancer and detection rates of carcinoma in situ lesions in Finland from 1953 to 1980.
9
cervical cancer were very stable for women under the age of 30 in the 1960s and 1970s. The number of cases is extremely low below the age of 30. Since 1960 one new car,: has been diagnosed annually below the age of 25 and fewer than 10 in the age group 25 to 29 in the total Finnish population. However, prevention of such cases by extension of the programme to lower age groups would considerably increase the cost per case detected. Moreover. comparison of the age-specific incidence of preinvasive lesions with that of invasive cancer indicates that the younger the women are the lower the probability of transition from preinvasive to invasive lesions is likely to be. This finding is also supported by the increase in dysplasias at these ages without any similar increase in the risk of invasive disease. The adverse effects in terms of treatment of lesions which would not progress if left untreated therefore also increase and it is likely that organized screening of women aged under 30 will not be recommended in Finland. The changes observed in the risk at age 60 and over have been relatively small. These ages were not covered by the screening programme but the women concerned by now, belong to cohorts which have been screened previously. In some other populations the changes in risk at later ages have also been found to be relatively small. It is possible that the screening is less effective at more advanced ages. Where the screening has in principle had an effect it is likely that it has been carried out more frequently. In summary, it would appear that, with the present resources available, close to the optimal range of age groups is covered by the programme. Screening under the programme in Finland is carried out very infrequently namely once every five years, as compared with the recommended one-year interval. However, since one of the greatest impacts on the risk that has ever been reported anywhere was achieved with the Finnish programme, it is unlikely that the overall system will be changed. The cost of the programme could be reduced if women at high risk for cervical cancer were screened and low-risk women were not. The high-risk women are those who have early sexual experience and multiple partners. Such characteristics are obviously of little practical use for the purposes of identifying a group that should be screened. Indirect indicators of risk, such as low social status, are not specific enough, and a major proportion of the cases stem from a low-risk group. Similar results were also found for other diseases, e.g. the DOM (Diagnostisch Onderzoek Mammacarcinoom *) project identified a high-risk group comprising one-third of the population, which at the most included two-thirds of all breast cancers [5]. Another type of risk factor is related to the pathological process itself, Women with positive cytology or who show symptoms without positive histology are at high risk during the subsequent follow-up period. Under the Finnish system the relevant data stemming from the previous screening are taken into account and the next invitation is sent out without waiting for the standard five-year interval to elapse. This is a recent change of approach which does not affect the rates reported here.
??
Breast Cancer Diagnostic Research Project.
10
Conclusion
The results of several screening programmes demonstrate rather conclusively that they effectively reduce the risk of cervical cancer [6-91. Even if screening for cervical cancer does not eradicate the disease, the magnitude of its effect compares favourably with that of several other health-related programmes having a high priority as far as the planning of programmes and allocation of resources are concerned. This evaluation of screening for cervical cancer in Finland refers solely to an organized programme and does not take into account the other smear testing activities in the country. Comparison of the Scandinavian countries confirms the fact that it is the organized programme which has an impact on cervical cancer risk and that the other activities are relatively ineffective [9]. The health care systems are rather similar in all the Scandinavian countries, cervical smears being taken quite frequently. In addition to normal gynaecological practice, Finland, Iceland and Sweden are fully covered by organized programmes. Denmark has an approximate coverage of 408, but there is no nationwide programme in Norway. The organized programmes in Finland and Sweden account for only between 20% .and something over 30% of all smears taken. There is nevertheless a close correlation between organized screening and reduction of the incidence of cervical cancer. The downward trend in incidence has been steepest in Iceland, followed by Finland and Sweden, whereas the incidence of cervical cancer in Norway was still increasing until very recently [9]. To summarize, it is likely that the quality of the smear, the validity of the cytological diagnosis and a high rate of attendance by the women involved are more important determinants of the success of screening for cervical cancer than coverage of a wide age span, repetition of smears at frequent intervals or concentration only on high-risk groups defined by epidemiological risk indicators. References 1 Kauraniemi T. Gynecological health screening by means of questionnaire and cytology. Acta Obstet Gynecol Stand 1969; 48 (suppl 4). 2 Kauppinen M, Kauraniemi T. Koli T, Voipio N. Response to the written invitation in a gynaecological mass screening by cytology arranged in Helsinki in 1966. Acta Obstet Gynecol Stand 1970; 49 (suppl 7): l-20. 3 Fortelius P, Haapoja H, Hakulinen T. The reasons for nonparticipation in vaginal cytological mass screenings (in Swedish). L&kartidningen 1974, 71: 3385-3387. 4 Hakama M, Rasanen-Virtanen U. Effect of a mass screening programme on the risk of cervical cancer. Am J Epidemiol 1976; 103: 512-517. 5 De Waard F. Rombach JJ, Collette HJA. The DOM-project for the early diagnosis of breast cancer in the city of Utrecht. the Netherlands. In: Miller AB, ed. Screening in cancer. Geneva: UlCC Technical Report Series, Vol 40. 1978. 6 Miller AB, ed. Screening in cancer. Geneva: UICC Technical Report Series, Vol. 40, 1978. 7 Johannesson G, Geirsson G, Day N. The effect of mass screening in Iceland 1965-1974 on the incidence and mortality of cervical carcinoma. Int J Cancer 1978; 21: 418-425. 8 Fidler HK, Boyes DA, Worth AJ. Cervical cancer detection in British Columbia. J Obstet Gynaecol Br Commonw 1968; 75: 392-404. 9 Hakama M. Trends in the incidence of cervical cancer in the Nordic countries. In: Magnus K, ed. Trends in cancer incidence. Washington: Hemisphere, 1982; 279-292.
MAT 00345
Effect of population screening for carcinoma of the uterine cervix in Finland M. Hakama Finnish Cancer Registry and University of Tampere, Finland (Received
26 December
1984: accepted
24 January
1985)
The organization of a nationwide population-based screening programme for cervical cancer in Finland is described. The annual incidence of invasive cervical cancer decreased from about 14 to 6 cases per 100,000 during the implementation of the programme. The time trends, age specificity and comparisons with other countries support the conclusion that the organized screening programme was effective in reducing the risk. However, there is no convincing evidence in support of expanding the overall programme to cover a wider age span than 30 to 60 yr or of screening the individual woman more frequently than once every 5 yr, even though these are the current recommendations.
(Key words:
Cancer
of cervix uteri, Population
screening,
Evaluation
of screening
programme)
Introduction Screening for cancer is aimed at detecting preclinical cases of cancer, the objective being to reduce the mortality rate. Cervical cancer has a detectable preinvasive stage and cervical screening therefore aims alternatively at reducing invasive disease. Because total eradication is an impracticable goal and only reduction of the risk is a realistic objective, a balance must be found between the yield and the cost of any screening programme. The yield is the proportion of cases detected by screening out of all the cases diagnosed in the target population. This proportion is related to the reduction in the risk of cervical cancer in the population. One indicator of the cost is the number of women who decide to participate in the programme. The overall cost is directly related not only to the financial cost but also to the possible adverse effects of screening, the latter being a cost factor that is often difficult to assess accurately. The yield and the cost are inversely related and the optimum should be decided upon in advance for any screening programme. There is no scientific method for finding the right balance, since any screening activity is either explicitly or at times
Correspondence to: M. Hakama, SF-33101 Tampere 10, Finland
0378-5122/85/.$03.30
University
of Tampere,
0 1985 Elsevier Science Publishers
Department
B.V.
of Public
Health,
P.O. Box 607.
implicitly based on a series of subjective judgements. The purpose of this paper is to describe how cervical screening is organized in Finland and to relate this to the observed changes in the incidence. In other words, the yield and cost of cervical screening in Finland and the relationship between these factors will be described.
Organizationof the programme
Mass screening was started by the Cancer Society of Finland in the early 1960s. A permanent programme was introduced under which the Finnish female population in the high-risk age groups for cervical cancer is screened every 5 yr. The individual municipalities are responsible for health care in Finland, but the cost is subsidized by the government. The municipalities consequently decide the extent to which women are screened, i.e. the specific cohorts to be screened. The Cancer Society of Finland originally recommended that the 1-yr cohorts aged 40,45 and 50 yr be screened. From the outset, however, there were some deviations from the recommended ages and some variation between the municipalities. In recent years it has been common to have the first screening at age 30 and to continue up to the age of 55. Women eligible for screening are selected by computer from the national population registry. A letter of invitation, with information on the place and time of the screening, is mailed to those selected to participate in the programme. Smears are taken as a rule at local maternity centres by public health nurses or midwives. A notification card is completed with a set of anamnestic data in an interview at the time the smear is taken. The smears are analyzed at the cytological laboratories of the Finnish Cancer Society and all the women participating are notified of the results. Women with malignant or suspected lesions are urged to have further examinations carried out at a specified hospital, which is responsible for reporting diagnostic confirmations together with details of any treatment to the laboratory concerned. The laboratories send full details to the national mass screening registry, which operates within the Finnish Cancer Registry, where the data are linked with the original population data and with any record of previous screenings. The national population registry data, the reports to the Finnish Cancer Registry on all cervical cancer cases diagnosed in the country and the reports on mass screening form the basis for the close surveillance that is maintained of trends in the risk of contracting cervical cancer. The number of annual smears taken under the organized screening programme gradually increased from 2000 in 1963 to roughly 120,000 by 1980, which is equal to about five 1-yr birth cohorts. In addition to those handled under organized screening programme, cytological smears are also commonly taken in general gynaecological practice. The organ&d mass screening smears comprise only one-third to one-fourth of all smears taken in Finland [l]. No exact figures on the overall number of smears are available.
5
Research to predict the ultimate reduction in risk
The risk of cervical cancer before screening, the risk among attenders after the first smear, the risk among non-attenders and the participation rate are all determinants of the ultimate reduction in risk achieved by a screening programme. The registration of the mass screenings, linked with the information obtained from the national population registry and the Finnish Cancer Registry provided the data necessary to predict the effect of screening on the risk at the population level. The first organized screening programmes in the early 1960s resulted in a relatively high rate of attendance - about 80% [l]. There has since been an increase in the rate of non-response, but the rate of attendance is still between 70 and 80%. It is well known that the non-response rate is often affected by self selection resulting in non-participation by the high-risk woman. In Finland no overrepresentation of the high-risk indicators of cervical cancer was found among non-attenders [2]. The women who attended were neither of high social status nor younger than average. Common reasons for non-attendance were recent removal from the municipality resulting in an incorrect mailing address in the national population registry or a recent smear carried out by a private gynaecologist or elsewhere. Only about one-third of those not attending had an unacceptable reason for failing to participate [3]. It was possible to make a direct estimation of the risk of cervical cancer among non-responders by linking up data from the register of invitations, the register of responders and the Finnish Cancer Registry (41. It turned out that while no obvious risk factors characterized those who failed to respond, their cervical cancer risk was 1.7 times that among the overall population before the time of screening or among those not covered by the programme. The estimates of the ultimate reduction in the incidence of cervical cancer assume follow-up after the first screening. On the basis of the first 70,000 women attending for the second time it was found that among those participating the risk of frankly invasive cervical cancer was about 20% of that among those not covered by the programme. When all these results were combined it was predicted that at the population level an approximately 60% reduction in the incidence of frankly invasive cancer should be achieved [4] after the programme had had its full impact. During later years it was possible to assess the accuracy of this prediction.
Effect of the programme at the population level
The simplest indicator of the effect of the programme at population level is the number of cervical cancer cases. Before intensive screening began about 400 new cases of invasive cervical cancer were diagnosed annually. In 1980 there were only 181 new cases of cervical cancer (Fig. l), representing a substantial fall which corresponds roughly to the 60% reduction in the risk that was predicted. The changes in the incidence of cervical cancer correlate with the intensity of the
6 CERVIX
No.ofCases
UTERI
500 1
,,,,,,,.,,,,.,,,
)
855
1960
1965
1970
1915
19Ei
FINNISH CANCER REGISTRY
Fig. 1. Annual number of cases of invasive cervical cancer and in situ lesions in Finland in 1953-1980.
screening programme by age. Fig. 2 shows the age-specific incidence rates in the age groups spanning the 30 to 54 age band. Up to the age of 50 yr, the reduction in the age-specific incidence over the period from the 1950s to the 1970s was 70% or more.
Per IO5
INVASIVE CARCINOHAOFCERVIX
UTERI
50.
co30 -
20 -
10 as43. 2,
Fig. 2. Trends in the age-specific incidence of cervical cancer in Finland for age yr.
groups30-34 to 50-54
Per 10'
INVASIVE CARCINOMA OF CERVIX
Fig. 3. Trends in the age-specific
UTERI
incidence of cervical cancer in Finland for age groups 55-59
to 65-69
v.
The most substantial reduction occurred between 1967 and 1974. Outside that period the changes were smaller and less regular. The changes in the incidence of cervical cancer at age 60 and over were relatively small (Fig. 3). The rates by birth cohort (Fig. 4) confirm the decrease and indicate an abrupt time effect on the rates, which fit well with the intensity of screening. Fig. 5 shows the overall trends in the incidence of cervical cancer and the resultant mortality as well as the trend for carcinoma in situ lesions. There were some discrepancies between the official death certificate diagnoses and information derived from the cancer registry, especially in the early years. The official mortality rates were therefore corrected in accordance with the cancer registry data for the 1950s and 1960s. The total overall age-adjusted incidence was about 14 per 100,000 before the period of intensive screening and by 1980 this rate had fallen to 5.
Alternative programmes
There can be little doubt as to the overall efficacy of screening for cervical cancer. However, no reliable evidence is available in regard to several important aspects of such a programme. The recommendations vary, for example, as to the ages to be covered by screening and to its frequency. Several reports have pointed out an increase in the frequency of cervical lesions among young women. In particular, there has been an increase in the incidence of carcinoma in situ lesions and severe dysplasias. In Finland the rates for invasive
8
FINLAND
J
20
30
40
50
60
70
80
AGE
Fig. 4. Age-specific incidence of cervical cancer in Finland by selected birth cohorts. The dates refer to mid-year of birth for a S-yr age- and time-specific rate. Per 10' 16
CERVIX
UTERI Invasive:incidence
14
6
2 0 FINNISH CANCER REGISTRY
0
Fig. 5. Annual age-adjusted incidence and mortality rates of invasive cervical cancer and detection rates of carcinoma in situ lesions in Finland from 1953 to 1980.
9
cervical cancer were very stable for women under the age of 30 in the 1960s and 1970s. The number of cases is extremely low below the age of 30. Since 1960 one new car,: has been diagnosed annually below the age of 25 and fewer than 10 in the age group 25 to 29 in the total Finnish population. However, prevention of such cases by extension of the programme to lower age groups would considerably increase the cost per case detected. Moreover. comparison of the age-specific incidence of preinvasive lesions with that of invasive cancer indicates that the younger the women are the lower the probability of transition from preinvasive to invasive lesions is likely to be. This finding is also supported by the increase in dysplasias at these ages without any similar increase in the risk of invasive disease. The adverse effects in terms of treatment of lesions which would not progress if left untreated therefore also increase and it is likely that organized screening of women aged under 30 will not be recommended in Finland. The changes observed in the risk at age 60 and over have been relatively small. These ages were not covered by the screening programme but the women concerned by now, belong to cohorts which have been screened previously. In some other populations the changes in risk at later ages have also been found to be relatively small. It is possible that the screening is less effective at more advanced ages. Where the screening has in principle had an effect it is likely that it has been carried out more frequently. In summary, it would appear that, with the present resources available, close to the optimal range of age groups is covered by the programme. Screening under the programme in Finland is carried out very infrequently namely once every five years, as compared with the recommended one-year interval. However, since one of the greatest impacts on the risk that has ever been reported anywhere was achieved with the Finnish programme, it is unlikely that the overall system will be changed. The cost of the programme could be reduced if women at high risk for cervical cancer were screened and low-risk women were not. The high-risk women are those who have early sexual experience and multiple partners. Such characteristics are obviously of little practical use for the purposes of identifying a group that should be screened. Indirect indicators of risk, such as low social status, are not specific enough, and a major proportion of the cases stem from a low-risk group. Similar results were also found for other diseases, e.g. the DOM (Diagnostisch Onderzoek Mammacarcinoom *) project identified a high-risk group comprising one-third of the population, which at the most included two-thirds of all breast cancers [5]. Another type of risk factor is related to the pathological process itself, Women with positive cytology or who show symptoms without positive histology are at high risk during the subsequent follow-up period. Under the Finnish system the relevant data stemming from the previous screening are taken into account and the next invitation is sent out without waiting for the standard five-year interval to elapse. This is a recent change of approach which does not affect the rates reported here.
??
Breast Cancer Diagnostic Research Project.
10
Conclusion
The results of several screening programmes demonstrate rather conclusively that they effectively reduce the risk of cervical cancer [6-91. Even if screening for cervical cancer does not eradicate the disease, the magnitude of its effect compares favourably with that of several other health-related programmes having a high priority as far as the planning of programmes and allocation of resources are concerned. This evaluation of screening for cervical cancer in Finland refers solely to an organized programme and does not take into account the other smear testing activities in the country. Comparison of the Scandinavian countries confirms the fact that it is the organized programme which has an impact on cervical cancer risk and that the other activities are relatively ineffective [9]. The health care systems are rather similar in all the Scandinavian countries, cervical smears being taken quite frequently. In addition to normal gynaecological practice, Finland, Iceland and Sweden are fully covered by organized programmes. Denmark has an approximate coverage of 408, but there is no nationwide programme in Norway. The organized programmes in Finland and Sweden account for only between 20% .and something over 30% of all smears taken. There is nevertheless a close correlation between organized screening and reduction of the incidence of cervical cancer. The downward trend in incidence has been steepest in Iceland, followed by Finland and Sweden, whereas the incidence of cervical cancer in Norway was still increasing until very recently [9]. To summarize, it is likely that the quality of the smear, the validity of the cytological diagnosis and a high rate of attendance by the women involved are more important determinants of the success of screening for cervical cancer than coverage of a wide age span, repetition of smears at frequent intervals or concentration only on high-risk groups defined by epidemiological risk indicators. References 1 Kauraniemi T. Gynecological health screening by means of questionnaire and cytology. Acta Obstet Gynecol Stand 1969; 48 (suppl 4). 2 Kauppinen M, Kauraniemi T. Koli T, Voipio N. Response to the written invitation in a gynaecological mass screening by cytology arranged in Helsinki in 1966. Acta Obstet Gynecol Stand 1970; 49 (suppl 7): l-20. 3 Fortelius P, Haapoja H, Hakulinen T. The reasons for nonparticipation in vaginal cytological mass screenings (in Swedish). L&kartidningen 1974, 71: 3385-3387. 4 Hakama M, Rasanen-Virtanen U. Effect of a mass screening programme on the risk of cervical cancer. Am J Epidemiol 1976; 103: 512-517. 5 De Waard F. Rombach JJ, Collette HJA. The DOM-project for the early diagnosis of breast cancer in the city of Utrecht. the Netherlands. In: Miller AB, ed. Screening in cancer. Geneva: UlCC Technical Report Series, Vol 40. 1978. 6 Miller AB, ed. Screening in cancer. Geneva: UICC Technical Report Series, Vol. 40, 1978. 7 Johannesson G, Geirsson G, Day N. The effect of mass screening in Iceland 1965-1974 on the incidence and mortality of cervical carcinoma. Int J Cancer 1978; 21: 418-425. 8 Fidler HK, Boyes DA, Worth AJ. Cervical cancer detection in British Columbia. J Obstet Gynaecol Br Commonw 1968; 75: 392-404. 9 Hakama M. Trends in the incidence of cervical cancer in the Nordic countries. In: Magnus K, ed. Trends in cancer incidence. Washington: Hemisphere, 1982; 279-292.