Hereditary Ovarian Cancer Reduced by Oral Contraceptives
Frederick R. Jelovsek MD
We've known since the early 1990's that use of birth control pills reduces a woman's risk for ovarian cancer by about 50%. The exact mechanism isn't known but it has been postulated that by keeping the ovary from ovulation each month, this reduces the exposure of the ovary to any cancer causing viruses or toxins. At ovulation, the inside of the ovary is opened in order to release an egg.
Causes of Ovarian Cancer
About 5 to possibly 10% of ovarian cancer, however, is associated with a genetic predisposition; it occurs in women with mutations in the BRCA1 or BRCA2 gene. If a woman has a BRCA1 mutation, her lifetime incidence of ovarian cancer is about 45% instead of the usual 1.4% in the general population. If there is a BRCA2 gene mutation, there is approximately a 25% lifetime incidence of ovarian cancer. For women who are known to have these gene mutations, the only suggested risk reduction therapies have been prophylactic oophorectomy and ultrasound screening, neither of which have been used enough to know the extent of the risk reduction.
How Oral Contraceptives Helps
In a recent article, Narod SA et al.: Oral contraceptives and the risk of ovarian cancer. N Engl J Med 1998; 339:424-8, the authors looked at whether or not oral contraceptives reduced the incidence of ovarian cancer in women who had a genetic risk by having either the BRCA1 or BRCA2 gene. They found that women who used oral contraceptives in the past were at lower risk for ovarian cancer even if they were positive for either BRCA gene. The magnitude of reduction was the same as it was for women overall, i.e., if women had used the pills 3 or less years, their risk was 80% of the risk for non-pill users. If a woman had used the pills for 3-6 years, her risk was 40%. Basically the risk dropped by 10% for each year the pill had been used although there did not seem to be a further reduction after 6 years of use.
There were some limitations of this study so we will hope that others also research this subject. For now, the data suggests that oral contraceptives should be part of a program of prevention for women with known BRCA1 or BRCA2 mutations.
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