Neoplasia of the cervix uteri and contraception: a possible adverse effect of the pill.

The incidence of biopsy-proven cervical neoplasia during a 10-year follow-up was determined in 6838 parous women who entered the Oxford-Family Planning Association contraceptive study while using oral contraceptives and 3154 parous women who entered the study while using an intrauterine device (IUD). Risk factors for cervical neoplasia, continuation of attendance at family planning clinics, and frequency of examination by cervical cytology were similar in the two groups. All 13 cases of invasive cancer occurred in women in the oral contraceptive group; 9 had more than 6 years' use of the pill. Both carcinoma-in-situ and dysplasia also occurred more frequently in the oral contraceptive group than in the IUD group, and when the two conditions were considered together there was a trend in incidence with duration of oral contraceptive use. The incidence for all three forms of neoplasia combined rose from 0.9 per 1000 woman-years in those with up to 2 years' pill use to 2.2 per 1000 woman-years in those with more than 8 years' pill use. Amongst IUD users, there was no such trend in incidence with duration of use: the rate fluctuated around 1.0 per 1000 woman-years. The great majority of cases of invasive cancer were detected by means of cervical smears and were treated while the disease was still curable. Long-term users of oral contraceptives should have regular cervical cytological examination.