Changes in cervical cancer incidence after three decades of screening US women less than 30 years old.

OBJECTIVE: To examine incidence trends of invasive cervical carcinoma in US women less than 30 years old from 1973 to 1999 by histologic type.
METHODS: Incidence rates were obtained from the National Cancer Institute's Surveillance, Epidemiology and End Results (SEER) database and stratified by age and three histologic categories: all histologic types, squamous cell carcinoma, and adenocarcinoma. The estimated annual percent change was calculated by joinpoint regression to measure trends during the entire evaluation period and a recent subperiod (1985-1999). All statistical tests were two-sided.
RESULTS: Incidence rates of cervical carcinoma overall and squamous cell carcinoma specifically declined during 1973-1999, with estimated annual percent changes of -0.94% (95% confidence interval [CI] -1.47%, -0.41%) and -1.10% (95% CI -1.59%, -0.62%), respectively. Rates of adenocarcinoma increased (+2.90%; 95% CI 1.34%, 4.49%), though trends have been stable since 1990. All cancers were uncommon: the annual incidence per million women ranged from 8.0 to 14.3 for squamous cell carcinoma and from 0.7 to 2.7 for adenocarcinoma. For women younger than 20 years, no statistically significant changes were observed, but cancers were rare (0-3 per million women annually).
CONCLUSIONS: More investigation is necessary to clarify the contribution of screening to declines in the squamous cell carcinoma rate and to determine the etiology of adenocarcinoma rate increases over the last three decades in US women less than 30 years old. Because of the small number of actual observed cases, caution must be exercised in interpreting these trends.