Invasive cervical cancer and combined oral contraceptives. WHO collaborative study of neoplasia and steroid contraceptives.

A multicentre, hospital based case-control study is being conducted under the auspices of the World Health Organisation to determine whether steroid contraceptives alter the risk of gynaecological, breast, and hepatic neoplasms. Preliminary results, largely from developing countries, on the relation between combined oral contraceptives and invasive cervical carcinoma showed a relative risk of 1.19 (95% confidence interval 0.99-1.44) in women who had ever used oral contraceptives. The risk increased with duration of use, giving a relative risk of 1.53 after five years. This finding supports a causal interpretation, but it could also be due to incomplete control for confounding sexual variables and other sources of bias.