| Abstract: | The response of the International Medical Advisory Panel (IMAP) of the International Planned Parenthood Federation to 2 recent papers suggesting a link between cancer and oral contraceptive (OC) use is reported. The 1st paper by Pike et al. suggested an increased risk of breast cancer in women who use OCs containing high potency progestogens before age 25 for at least 4 years. It is noted that several methodological problems with the study design could have introduced a degree of selection of ascertainment bias. These issues include the procedures used for age matching between cases and controls, the 1/3 loss to follow-up among cancer cases, and the use of telephone interviews to ascertain OC use history. Moreover, data from other studies suggest that ever-users of OCs who develop breast cancer may be more likely to survive than women with breast cancer who have never used OCs, leading to the overrepresentation of women in the former group among surviving cases. The ranking of OCs by progestogen potency does not take the estrogen content into consideration. In addition, assessment of progestogen potency by use of a delay of menses test may not correlate with the degree of effect on the breast and has produced conflicting results when used by different researchers. Finally, the numbers of women using some OC brands were too small and the possibility that women may have changed OC brand over the study period was not considered. Largescale studies such as the UK Oxford-Family Planning Association contraceptive study and the Centers for Disease Control Cancer and Steroidal Hormone Study are curently being reanalyzed, controlling for type and amount of progestogen in the OCs. Until new data become available, IMAP believes there is insufficient evidence to recommend modification of existing practice. The 2nd study by Vessey et al. suggested a higher incidence of cervical cancer in OC users as compared to IUD users. However, several key modifying factors on the risk of cervical cancer, including age at 1st sexual intercourse and number of partners, could not be controlled for. Moreover, a high proportion of OC use involved preparations containing 50 mcg or more of estrogen. Although regular cervical smears are recommended for OC users, the IMAP again does not recommend any change in current practice. The IMAP noted that the possible cancer-related risks of OCs must be weighed against the protective effects of OCs against cancers of the endometrium and ovary, pelvic inflammatory disease, and unwanted pregnancies. |
