Endometriosis
may increase the risk of certain cancers, but absolute
risk remains low
Epidemiological
studies presented at the 23rd annual meeting of ESHRE
showed a headline grabbing increased cancer risk among
women with endometriosis. But clinicians remind women
with endometriosis that in fact this research is reassuring
in that there appears to be no overall increased risk
of cancer.
LYON, 2 JULY
2007
According to Swedish researchers endometriosis
is associated with an increased risk of various cancers,
but this risk does not depend on the number of times
women with the condition have given birth.
Dr Anna-Sofia Melin, told the 23rd
annual meeting of the European Society of Human Reproduction
and Embryology today: “Several epidemiological
studies have shown an increased cancer risk among women
with endometriosis, especially ovarian cancer. Infertility
and never having given birth (nulliparity) are also
known risk factors for different types of cancer, such
as breast and endometrial cancer. However, as far as
we know, this is the first study to investigate cancer
risk among women with endometriosis that also stratifies
for parity.”
Dr Melin and epidemiologists at the
Karolinska Institute looked at data from 63,630 women
who had been discharged from hospital with a diagnosis
of endometriosis between 1969 and 2002. They were identified
and followed up via the National Swedish Inpatient Register,
the National Swedish Cancer Register and the Swedish
Multi-Generation Register.
The researchers identified 3,822 cases
of cancer amongst the women with endometriosis. While
they found no overall increased risk of cancer, they
did find that the women had an elevated risk of certain
types of rare cancer, but that there was no
significant difference in risk between women who had
never given birth and those who had.
“We found that, contrary to what
one might expect, endometriosis and nulliparity did
not combine to give a higher risk of cancer,”
said Dr Melin.
The researchers found that endometriosis
increased the risk of developing ovarian cancer by more
than a third (37%) above the risk for the normal population
of women without endometriosis. There were similar increases
in risk for endocrine tumours (38%), kidney cancer (36%)
and thyroid cancer (33%). Slightly lower increases were
found for brain tumours (27%) and malignant melanoma
(23%), and there was a small increased risk of breast
cancer (8%). Interestingly, women with endometriosis
had a reduced risk of cervical cancer of just under
a third (29%).
“There was no significant difference between nulliparous
and parous women with endometriosis regarding cancer
risk for any of the cancer types. We found a non-significant
decrease in ovarian cancer risk the more children a
woman had had,” said Dr Melin.
Little is known about the possible
mechanisms involved in the increased risk of cancer
from endometriosis (or decreased risk, in the case of
cervical cancer).
Dr Melin said: “The fact that
our study did not show an association between cancer
risk and parity increases the possibility that it is
the endometriosis disease in itself that causes the
cancer and not the infertility issue.
But she said that it was too early
to use the results of her study to give advice to doctors
about improved treatments for women with endometriosis.
“Our hope is that doctors in
general start to view endometriosis as a serious disease
that causes a lot of suffering to the patient and also
may lead to cancer. We hope that in the future we will
be able to identify those women with endometriosis that
may have a more aggressive form of disease with more
atypical cells, for instance, and that this may lead
to better care for the patient and, hopefully, to a
early diagnosis if cancer should occur,” she concluded.
Dr
Andrew Prentice, Senior Lecturer in Obstetrics and Gynaecology
at the University of Cambridge, commented:
"The data from the Karolinska
Institute is of great interest to women with endometriosis.
It is reassuring that women with endometriosis
do not have an overall increased risk of cancer.
What is not clear from the information available
is the strength of the observations in those cancers
where there has been shown to be an increased risk and
how many cases these observations are based on from
each cancer. It is not clear whether it is endometriosis
itself or endometriosis affecting the ovary that increases
the risk."
"Until a plausible biological
link exists between these cancers and the occurrence
of endometriosis or the reduction in cases for other
forms of cancer it is not clear how valuable this information
is. This research indicates a need for further research
to explore possible links and their mechanisms in order
that appropriate strategies can be developed for the
long term management of women with endometriosis"
said Dr Prentice.
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