NEW YORK, Mar 09 (Reuters Health) -- Women who use birth control pills have
a reduced risk of ovarian cancer, and scientists have assumed that this is due
to the prevention of ovulation and the hormonal changes that accompany it. Now,
three new studies suggest that the relationship is more complicated than
previously thought.
For example, the benefits of oral contraceptives may decline with age,
according to a report by Dr. Alice S. Whittemore of the Stanford University
School of Medicine in California, and colleagues.
The researchers tried to determine if the decline in ovarian cancer over the
past 30 years could be explained by an increase in women using birth control
pills and a decrease in child bearing.
In women under age 50, both these factors did seem to account for the
declining cancer rates. But women over age 50 had a higher rate of cancer than
would be expected, suggesting that "the protective effect of oral contraceptive
use declines with age," the study authors write in the March issue of
Epidemiology.
In a second report in the journal, Dr. Victor Siskind of the Queensland
Institute of Medical Research in Australia, and colleagues suggest that oral
contraceptives reduced the risk of ovarian cancer by 7% per year of use, and
that there may be an additional benefit of using the drug before the first
pregnancy.
The Australian team compared 794 women with cancer to 853 cancer-free women,
and found that the decreased risk applied to all three major types of ovarian
cancer, as well as to borderline and malignant tumors. Oral contraceptives may
protect against cancer by suppressing the hormone androgen and increasing
another hormone, progesterone, they conclude.
The third study, conducted by Dr. Roberta B. Ness of the University of
Pittsburgh, Pennsylvania, and colleagues, reports that inflammation may play a
role in ovarian cancer development.
The researchers found that oral contraceptives did indeed decrease cancer
risk, but other factors did as well. Women who had been pregnant, nursed a baby,
had a tubal ligation or a hysterectomy were at lower risk of ovarian cancer.
Some factors increased the risk of the cancer, including the use of talc powder
on any area of the body or on underwear, or having endometriosis or ovarian
cysts -- conditions that may irritate and inflame the ovaries.
The study, which included 767 women with cancer and 1,367 cancer-free women,
supports the theory that "inflammation at the site of the ovarian epithelium is
associated with ovarian cancer risk," Ness and colleagues conclude. They suggest
that substances that are produced when tissue is irritated, such as cytokines
(cell-signaling molecules), prostaglandins (hormone-like compounds that have
many effects on the body), and growth factors, may lead to the development of
cancer cells.
The three studies suggest new mechanisms for the protective effects of oral
contraceptives, according to an editorial by Drs. Ingemar Persson and Tomas
Riman of the Karolinska Institute in Stockholm, Sweden. They also note that the
research suggests that ovarian cancer is directly affected by hormones and
ovarian inflammation.
