Oral contraceptives and cervical cancer risk in Costa Rica. Detection bias or causal association?
K. L. Irwin, L. Rosero-Bixby, M. W. Oberle, N. C. Lee, A. S. Whatley, J. A. Fortney and M. G. Bonhomme
Division of Reproductive Health, Centers for Disease Control, Atlanta, GA 30333.
To examine the relationship between cervical cancer and oral contraceptive
(OC) use, we analyzed data from a population-based, case-control study in
Costa Rica. Women aged 25 to 58 years in whom cervical cancer was diagnosed
and reported to the National Tumor Registry were examined as two separate
case groups: invasive cervical cancer and carcinoma in situ (CIS). Controls
were women aged 25 to 58 years identified through a national survey. Women
who had used OCs had no increased risk of invasive cervical cancer compared
with women who had never used OCs (relative risk, 0.8; 95% confidence
interval, 0.5 to 1.3). Women who had used OCs had an increased risk of CIS
compared with those who had never used OCs (relative risk, 1.6; 95%
confidence interval, 1.2 to 2.2). However, further analyses indicated that
this increased risk was confined to those who had recently used OCs. Also,
the risk of CIS was not elevated in subgroups in which a history of
cervical smears was not strongly linked to OC use. The elevated risk of CIS
among OC users may therefore reflect a bias caused by enhanced detection of
disease rather than a causal association.
