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Drs. Thomas and Noonan reply re "Comparison of Recalled and Validated Oral Contraceptive Histories" [letter]
AMERICAN JOURNAL OF EPIDEMIOLOGY. 1995 Apr 15; 141(8):791.Dr. Realini asserts in his letter that the results of the WHO Collaborative Study of Neoplasia and Steroid Contraceptives concerning oral contraceptives and breast cancer could have been biased as a result of better recall of prior oral contraceptive use by cases in comparison to controls. Although this is a possibility in any case-control study based on data collected by interviews, being able to validate positive oral contraceptive histories of more cases than controls does not necessarily mean more cases than controls who were users of oral contraceptives gave a history of such use. The issue of bias due to recall was discussed in the original paper. The medical records of women who claimed contraceptive use were checked for brand names and duration of use; the medical records of women who did not were not checked. This procedure did not alter their classification as users or nonusers. Since few combined oral contraceptives were available, and erroneous reports of use of combined or noncombined preparations were corrected, the estimated values of the relative risk of breast cancer in women who ever used combined oral contraceptives could not be appreciably influenced by any differences in the proportion of cases or controls whose oral contraceptive histories were supplemented by information from medical records. However, such differences could alter estimated values of the relative risk in relation to duration, latency, or recency. Information was obtained from the medical records of users in 27% of cases and 18% of controls. These percentages varied with center (0-94% of cases, 0-89% of controls). Information was most frequently obtained from the medical records of long-term and current or recent users in both groups. Similar results were obtained separately from countries in which information from medical records was obtained for relatively high and low proportions of users, and in individuals whose use was ascertained solely from interviews and from both interviews and medical records.
AMERICAN JOURNAL OF EPIDEMIOLOGY. 1994 Nov 15; 140(10):956.A paper by Nischan and colleagues, "Comparison of Recalled and Validated Oral Contraceptive Histories," which examines the accuracy of the histories of oral contraceptive use (defined as agreement with gynecologists' records concerning duration of use, times since first and last use, and individual preparations used) in a WHO case-control study of breast cancer, "WHO Collaborative Study of Neoplasia and Steroid Contraceptives," fails to comment on the more frequent validity of the histories among those persons with breast cancer. Of 253 contraceptive histories from persons with breast cancer, for whom responses from at least 1 gynecologist were available, 234 (92.4%) were confirmed; of those from 621 controls, 524 were. The difference is statistically significant (chi-square test, p < 0.01). This better recall of ever-use of oral contraceptives among breast cancer patients creates a bias that makes an association between breast cancer and ever-use of oral contraceptives stronger than it is. The slight elevation in breast cancer risk associated with ever-use of oral contraceptives found in the WHO study may be due to this. There is no information about the accuracy of negative oral contraceptive histories.
SOUTH AFRICAN MEDICAL JOURNAL. 1992 May 2; 81(9):444-5.The advantages and side effects of the injectable contraceptive, Depo-Provera, are highlighted. It has been available to women in South Africa and in about 90 developing and developed countries for 20 years. It is an effective and convenient contraceptive with no serious side effects. Its failure rate is 0.2-0.6/100 woman years. Nevertheless there is still concern that it may cause breast cancer because original tests of Depo-Provera using beagles indicated that it may increase breast cancer risk. WHO and the UK Committee on Safety of Medicines have since dropped the requirement of testing of beagles since they cannot predict the effects of steroids on women. A 12-year WHO multinational, hospital-based case-control study on neoplasia and hormonal contraceptives reassures Depo-Provera's safety. For example, the risk of breast cancer did not increase with duration or in women who had used it for >5 years. The risk was higher, however, among women who had used it for <4 years, particularly <35-year old women. The same holds true for oral contraceptive (OC) users. It has been suggested that this slight increase is because Depo-Provera and OCs may accelerate growth of some existing, previously undetected breast tumors. The WHO study verifies that the benefits of Depo-Provera surpass the side effects which include disturbed bleeding patterns, weight gain, and headaches. For example, it decreases the risk of ovarian and endometrial cancer. It is even more beneficial in developing countries where women often suffer from anemia because it increases hemoglobin levels. Further since women in developing countries cannot always comply and take their OCs, Depo-Provera can grant them the protection they need against pregnancy thus saving many lives. Depo-Provera should be available in developed as well as in developing countries.