Industry-funded German Women Cohort Predictably Shows Cancer Prevention by Oral Contraceptives
a recent publication by Lexchin et al.1 stated that the studies perused indicated "that researchers cannot predict results of trials in advance", when funding by pharmaceutical firms had been achieved. Had any of the studies included covered the calendar year of 2002 and publications from Germany as well, a contrasting statement might have been resulted.
Results from the German Cohort Study on Women's Health have been published indicating that use of oral contraceptives are protective of breast cancer2 as well as female genital cancers3 (ovary, cervix, endometrium) . The study funded by Schering AG, Berlin, Germany, a major producer of hormone drugs, is a retrospective cohort of volunteer women, aged 18 - 65, recruited by advertisements, sickness fund flyers a.o.. Data are collected retrospectively from the birth of women onwards using a mailed questionnaire.
Initiated in 1998, 15.374 women contributed 610.328 women years until 2002. Prevalent cancers were reported by participants and had til publication not been validated by any means. Number of cases for two cancer locations were greatly below expected numbers, as determined from Saarland Cancer Registry incidence rates (women until age 65): ovarian cancer 24 observed (O) vs. 40.4 expected (E); breast cancer O: 308 vs. E: 420.
These results had to be expected taking into account case fatality rates of respective cancers. Thus cases of breast cancer in younger women which tend to be more aggressive and of poorer prognosis are to be underrepresented as well as more advanced cases of ovarian cancer, as these women had to be already deceased when recruitment started.
For multivariate logistic regression exposure to oral contraceptives was censored with date of diagnosis in cases, but not in controls. These distortions of established epidemiologic procedures for cohort studies predictably lead to a major bias towards diminishing relative risk estimates.
1Lexchin J, Bero LA, Djulbegovic B, Clark O. Pharmaceutical industry sponsorship and research outcome quality: a systematic review. BMJ 2003; 326: 1167-1170.
2Heinemann LAJ, Lewis MA, Kühl-Habich D, Braendle W, Moehner S (on behalf of the German Cohort Study on Women's Health Research Group). The risk of breast tumors and lifetime history of oral contraceptive use. Geburtsh Frauenheilk 2002; 62: 750-757.
3Heinemann LAJ, Lewis MA, Kühl-Habich D, Braendle W, Garbe E, Moehner S. Lifetime history of oral contraceptive use and development of tumors of the uterus and ovary. Geburtsh Frauenheilk 2002; 62: 566-573.
Competing interests: No competing interests