[The Nordic cervical screening programmes through 1995. Evaluation of incidence and mortality rates, targeted age groups and screening intervals.].
BACKGROUND
The objective of cervical cancer screening is to lower the incidence and mortality rates of the disease. The Nordic countries have a long experience in cervical cancer screening. Based on this experience this study evaluates the UICC and EC guidelines regarding the effectiveness of organized vs. spontaneous screening, targeted age groups and screening intervals.


METHODS
The study analyses the features of the Icelandic and the Nordic screening programmes and the observed trends in the incidence and mortality rates in these countries through 1995. It also analyses the trends for cytologic preinvasive lesions at first visit and at second and later visits after a normal test(s). The frequency of histologic lesions was calculated for the birth cohort 1920-1926 from the age of 60 and among women referred for colposcopic examination in 1994.


RESULTS
Organized screening started in all the Nordic countries except Norway soon after 1960. Up to 1985 the target age group and screening interval were most intensive in Iceland. All countries intensified the screening intervals after 1985. The reduction in both the mortality and the incidence rates was greatest in Iceland and Finland, intermediate in Sweden and Denmark, and lowest in Norway but in that country organized screening started in 1994. The age-specific incidence in the 20-29 age group has been increasing since 1971 in all the Nordic countries, except in Finland. In Iceland screening has greatly affected the rate of all stages of squamous cell carcinoma, but not the rate of adeno-and adenosquamous carcinomas. The prevalence of preinvasive disease has increased significantly since 1980. The rate of moderate to high-grade cytologic changes begins increasing as early as at 20 years of age and moderate to high-grade histologic lesions start to accumulate at 24 to 36 months after a normal smear. The rate of these lesions decreases with the number of negative smears taken. Moderate to high-grade histologic lesions and invasive cancer are practically non-existent after the age of 60 among correctly screened women. A strong correlation is found between increased attendance rates and the proportion of cases diagnosed with a Pap smear at stages IA and IB occult. The latter cases mainly occur among women under the Hge of 45 and start to appear less than two years after a normal smear.


CONCLUSIONS
Well-organised screening is more effective than spontaneous screening in reducing the risk of cervical cancer. Screening should preferably start soon after age 20 with a screening interval of two to three years. The screening interval can pro-bably be extended to four years at the age of 50 and screening could stop at the age of 60 to 64 among regularly screened women.
K
K
Sigurdsson