Effect of type of screening laboratory on population-based occurrence of cervical lesions in Finland

The incidence of cervical cancer decreased in Finland over a 30-year period because of an effective screening program, but in the beginning of the 1990s it began to increase. Reasons for such an increase are variable: changes in sexual habits, shortcomings in attendance for screening and possibly variation in laboratory quality. We evaluated the impact of 3 laboratories in the greater Helsinki area on screening performance and on the incidence of invasive cervical cancer and preinvasive cervical lesions in the target population. We studied time trends, geographic differences in attendance and detection rates from screening and the incidence of invasive cancer in the greater Helsinki area (population about 1 million) during the 1990s, when screening was reorganized from the Cancer Society of Finland laboratory to the municipal one (Helsinki) and to a private laboratory (Espoo), while in Vantaa screening remained with the same Cancer Society laboratory. The attendance rate for screening increased during the study period in all 3 cities. The numbers of cytologically suspected and histologically confirmed precancerous lesions found, including severe lesions, decreased significantly with the change of laboratory in Espoo; but in Helsinki and Vantaa, they increased. The overall incidence of invasive cervical cancer increased in all cities in the age groups screened but mostly in Espoo. The rather rapid changes and variation in trends in the number of screening findings cannot be explained by changes in etiologic factors or attendance. They may be related more to the quality of the laboratory performance and perhaps to the criteria used in cytology and colposcopy. A well-organized auditing system is proposed to maintain high quality in screening.