Age at beginning of coitus versus chronologic age as a basis for Papanicolaou smear screening: an analysis of 747 cases of preinvasive disease.

Disease onset in 747 routinely screened women who developed cervical intraepithelial neoplasia was analyzed. Average age at diagnosis was 30 years; the range was 16 to 71 years. In 19% diagnosis was made after age 35, and in 1% after age 60. Grouping cases by age at beginning of coitus produced significant differences (p less than 0.001) in cumulative proportions of patients with the diagnosis made at any age. In 11% of patients initiating intercourse between ages 15 and 17 diagnosis was made after age 35; the figure was 19% for the 18 to 19 age group and 36% for the 20+ group. Screening by chronologic age is effective for women initiating intercourse early. Screening by years of exposure to intercourse produced a uniform distribution regardless of age at beginning of coitus. In 75% the diagnosis was made within the first 15 years of intercourse, in 88% by year 20; and in 97% by year 30. In 70% the diagnosis was made between 6 and 20 years. Cytologic surveillance should be concentrated during the sixth through twentieth years when most cases develop.