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| Ovarian cancer includes cancers of diverse origin that appear in the ovaries. |
Ovarian cancer causes more deaths than any other
cancer of the female reproductive system. Evidence
now points to different types of ovarian cancer with
distinct origins, but they remain grouped together
because they first become evident in the ovaries.
The risk of a woman developing each type seems to
be affected by her reproductive history. Experts
have known for some time that the number of
children a woman has and her use of contraception
can influence her risk of ovarian cancer.
A team led by Dr. Kezia Gaitskell, a pathologist
based at the Cancer Epidemiology Unit of the
University of Oxford, set out to find out more about
different types of the disease.
They used data from the UK Million Women Study -
a longitudinal study of 1,146,985 women aged over
50 at recruitment. There were 7,570 incident cases
of ovarian cancer recorded after an average of 13
years of follow-up.
Having one child reduces risk by 20 %
The risk of the four most common types of ovarian
cancer was examined in women with different
childbearing patterns: serous, mucinous,
endometrioid and clear cell tumors.
Women with one child had a 20% reduction in risk
of ovarian cancer overall, compared with women
without children, and about a 40% reduction of risk
for endometrioid and clear cell tumors. Each
additional birth decreased the overall risk of ovarian
cancer by an estimated 8%.
Whether or not they had ever breastfed seems to
make no difference, although longer durations of
breastfeeding appear to mitigate the risk.
Fast facts about ovarian cancer
• Ovarian cancer is the eighth most
common cancer for women
• It is the fifth leading cause of cancer
death
• Over 20,000 women a year are
diagnosed with ovarian cancer in the US.
Learn more about ovarian cancer
Researchers also assessed the risk for women who
had undergone surgery to cut or clip their fallopian
tubes, a surgical procedure for permanent
contraception known as tubal ligation, or
sterilization.
The surgery appears to reduce the overall risk of
ovarian cancer by 20%. It also decreases the risk of
high-grade serous tumors by 20%, the most
common type of ovarian cancer, and the risk of
endometrioid and clear cell tumors by 50%.
Dr. Gaitskell speculates that tubal ligation may
lower the risk by acting as a barrier that prevents
the abnormal cells from passing through the
fallopian tubes to the ovaries.
She explains that since the discovery that ovarian
cancer does not always originate in the ovaries,
understanding of the disease has changed radically.
For example, many of the most common, high-
grade serous tumors seem to start in the fallopian
tubes, while some endometrioid and clear cell
tumors may develop from endometriosis .
Conditions that cause infertility may be
risk factors
The fact that the significant reduction in risk among
women with one child compared with women
without children implies an association with certain
conditions that cause infertility . Endometriosis,
among other conditions, makes it harder for a
woman to conceive; these same conditions may
also increase the risk of specific types of ovarian
cancer.
Dr. Gaitskell comments:
Prof. Charlie Swanton, chair of the 2015 National
Cancer Research Institute Cancer Conference,
notes that it is important to know what affects the
risk of different types of ovarian cancer and the
factors that impact it.
He adds that the next step is to understand the
mechanisms behind the findings "to develop some
way to extend this lower risk to all women,
regardless of how many children they have."
Medical News Today recently reported that ovarian
transplants are proving safe and effective for
cancer patients.
Posted by: Philip Ochika