Oral contraceptives and breast cancer
Gay, J.W.; Cardwell, M.S.
Missouri Medicine 87(10): 763-767
1990
ISSN/ISBN: 0026-6620 PMID: 2259330 Document Number: 362699
In 1990, 13 million US women currently used oral contraceptives (OCs). In the early 1970s, researchers began to study the link between OC use and breast cancer. These studies did not show an adverse relationship. In 1983, however, a case control study in Los Angeles, California published its results and showed an adverse relationship. Specifically it demonstrated an increased risk of breast cancer in women 37 years old who took an OC before they were 25 years old. The risk increased with longer use and high potency progestins. Also in 1983, researchers from England reported an increased risk from OC use before the 1st term pregnancy. Further, in 1987, 1 of these researchers published the results of another study demonstrating increased risk of breast cancer with longer duration of OC use before the 1st term pregnancy. The Royal College of General Practitioners demonstrated in 1981 a greater risk of breast cancer only for women 30-34 years old at the time of diagnosis, but no overall risk. In 1988, the Royal College again observed an increased risk (3.3) in the same age group and the risk increased with parity of 1 (5.8). The US based Cancer and Steroid Hormone Study did not report in 1983 an increased risk of breast cancer for any subgroup, for any duration of use, or for any type of OC. In 1988, it reported, however, an increased risk of breast cancer before age 45 in women who had no children and had an early menarche (13 years old), especially those who took the OCs Ovulen and Demulen (ethynodiol diacetate). Risk increased with duration of use (1.3 for 4-7 years and 11.8 for 12 years). Other studies have supported findings of increased risk and findings of no increased risk. These inconsistencies may be due to different forms of bias. Nevertheless OCs may initiate and convert a normal cell into a cancer cell. They may also promote tumor growth.