Oral contraceptives and breast cancer in young women. Some notes on a current controversy.

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A number of studies have examined the possible association of oral contraceptive (OC) use and the risk of breast cancer in young women since a World Health Organization (WHO) scientific group stated in 1978 that there is no firm evidence in accumulated data to suggest either an adverse or a beneficial effect of OC use on breast cancer risk. The group did state that some evidence exists suggesting that OCs may increase the risk of breast cancer among certain categories of women i.e. young women women with benign breast neoplasia and women using drugs prior to giving birth to their 1st child. The group emphasized that the evidence available at that time applied only to relatively short periods of OC exposure and for a very limited period of followup and that no inference could therefore be drawn about the longterm effects of OCs on subsequent risk of breast cancer. Kalache et al. have presented a comprehensive review of the findings up to 1983. These conclusions were largely in agreement with the statement of the WHO scientific group. To the subgroups of women whose risk of developing breast cancer was heightened by using OCs Kalache et at. added very young women nulliparous women women with a positive family history and women of perimenopausal age. Since the Kalache review a few additional studies have been published. This paper summarizes the findings of some of the most recent investigations dealing with the current controversy over the safety of OCs with regard to breast cancer in young women. Pike et al. (1983) suggested a substantially increased risk of breast cancer for young women who had taken OCs for 4 years or more before age 25. The relative risk of breast cancer in relation to OC use before age 25 was 2 with 95% confidence limits for 4-6 years of OC use and 4.9 for more than 6 years of OC use. Pike et al. also analyzed the risk of breast cancer relative to the progestagen potency of OCs as defined and found that the risk increase was confined to OCs with high progestagen potency only. Shortly after the Pike et al. study McPherson et al. presented similar results from an ongoing study of 247 married women recruited since 1980 and the same number of age and hospital matched married controls. The estimated relative risk for breast cancer for women who had used OCs for 4 or more years prior to their 1st fullterm pregnancy was 3.1 and for 1-3 years of use. Le et al. reported preliminary results in 1984 from an ongoing case-control study in France; OC use was not found to be associated with increased risk of breast cancer in this study. Stadel et al. reported in 1985 for 2573 eligible cases of breast cancer in women aged 20-44 years in the US that there was no significant increase in the risk of breast cancer for OC users according to age at 1st use or duration of use before age of 25 or before 1st fullterm pregnancy.