Sensitivity of the screening program for cervical cancer in the Florence District.

Cervical cancer screening has been ongoing in the Florence district since 1966. All invasive cervical cancers occurring from 1975 to 1985 in the district have been considered and their screening histories have been investigated to estimate screening sensitivity. In the years 1975-1984, 236,045 women were screened initially. In this population all interval cancers have been recorded to estimate first screening sensitivity values according to the length of the interval since the first Pap test: 0.90 at 1 year, 0.78 at 3 years, and 0.68 at 5 years. Sensitivity values for subsequent screenings were lower than those for the first screening (0.68 at 1 year, 0.43 at 3 years), probably due to a lower number of prevalent cancers and to a progressive selection of cancers which are difficult to detect. The high sensitivity values confirm our choice of a screening frequency of 3 years.