Oral contraceptives and breast cancer. A meta-analysis
Delgado-Rodriguez, M.; Sillero-Arenas, M.; Rodriguez-Contreras, R.; López Gigosos, R.; Gàlvez Vargas, R.
Revue d'Epidemiologie et de Sante Publique 39(2): 165-181
1991
ISSN/ISBN: 0398-7620 PMID: 1830968 Document Number: 369219
40 case control and 7 cohort studies of the link between oral contraceptives and breast cancer were combined in a meta-analysis by the method of Woolf to estimate overall relative risks. Articles were found by a Medline search from January 1966-June 1990, a hand search of the references, and a journal search for 1990. Papers were graded for bias by 2 blinded readers. The analysis of the 39 studies considered unbiased generated a global relative risk of 1.06, and an increased risk of 1.06, and an increased risk of 1.14 for premenopausal breast cancer. For premenopausal cancer, risks were 1.25 for use before age 24, and 1.17 for use before the 1st term pregnancy. A significant linear dose response was seen, in terms of months of exposure. There was an indication of latency, since risk estimates were higher from data collected after 1981. There was no evidence of a relationship between pill use and parity, family history, or history of benign breast disease. The dad are consistent with the theory that oral contraceptives can be acting as cancer initiators or promoters. There was not enough data to judge whether users of current lower dose pills have lower risks for premenopausal breast cancer. Future studies should address the difference between premenopausal and postmenopausal cancer.