Endometriosis and Cancer

Introduction
Definition
Incidence
Cause
Symptoms
Intestinal Endometriosis
Infertility
Diagnosis
Treatment
Adenomyosis
Are you too young to have
a laparoscopy?
Endometriosis and cancer
Treatment summary
Endometriosis and heredity

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One question frequently asked by women with endometriosis concerns the possible relationship between their endometriosis and the development of some form of cancer. There has not been much data developed concerning this issue but there has been some recent publications offering some new information.

There are several issues that need discussion. First, is whether or not endometriosis itself becomes malignant.

I treat as much if not more endometriosis than anyone else in the metropolitan Philadelphia area. In over twenty-five years of practice, I have only seen one case of endometriosis itself become malignant. Therefore, such a transformation must be exceedingly rare.

This becomes a relevant issue when women with a history of endometriosis either undergo a hysterectomy or go through natural menopause. In the discussions that I have with these women, I am frequently asked whether the estrogen therapy will stimulate the endometriosis (it might) and whether that stimulation will cause it to become malignant (we don't know). It is certainly well established that if a woman still has her uterus and is given estrogen alone (without progesterone) there is a small but measurable increase in the risk of developing uterine (endometrial) cancer.

Since endometriosis implants are in fact endometrium, it would seem reasonable to conclude that they too are capable of undergoing the same sort of malignant transformation as the normal endometrium inside the uterus. However, I have never seen this happen. The one case of endometrioid cancer arising in endometriosis that I have seen occurred in a premenopausal woman who had not been taking any Hormone Replacement Therapy.

It must be kept in mind that the endometrium in the endometriosis implants is not normal endometrial tissue. Studies have been done that show this tissue does not always respond to hormones the same way the normal tissue inside the uterus responds. This may serve as a protective mechanism.

Another issue is the fact that it has only been relatively recently that large numbers of postmenopausal women with a history of endometriosis have been given Hormone Replacement Therapy. It will take another five to ten years to determine whether there is cause for concern.

The other major issue is whether women who have endometriosis are at increased risk to develop other forms of cancer. A recent study from Sweden suggests that women with a history of endometriosis are more likely to develop breast cancer, thyroid cancer and non-Hodgkin's Lymphoma. These cancers were noted to be more common in women with non-ovarian endometriosis and adenomyosis.

An increased risk of ovarian cancer was noted in women with ovarian endometriosis.
This is the first report that I have seen suggesting an increased risk of these cancers in women with endometriosis. The fact that this report came from Sweden may been significant. I have seen other epidemiological studies reported from Sweden where the statistics were faulty. Many of these studies looked at small groups of patients and then tried to project those numbers onto a larger population. These kinds of statistical analyses may suggest a relationship but do not prove it definitely.

The question naturally arises - why do women with endometriosis develop these cancers more frequently? It is less likely that having endometriosis itself somehow predisposes women to develop these cancers. It is much more likely that women with endometriosis develop these cancers because they share common causes.

As I have indicated elsewhere in this pamphlet, there is now overwhelming evidence that environmental pollution plays a major role in the development of endometriosis. Endometriosis can be induced experimentally in monkeys by giving them PCB's and dioxin. We know that our environment is heavily polluted with both of these substances.

There is also very strong evidence suggesting that breast cancer is related to PCB and dioxin. The chemical industry does not want you to know this because they are afraid of the lawsuits that will be generated. Nonetheless, there is good data to suggest a strong link. Since both endometriosis and breast cancer are linked to dioxin, this may be the common denominator.

There is also evidence linking non-Hodgkin's Lymphoma to environmental pollution as well.

It is not so easy to develop a common link between ovarian endometriosis and ovarian cancer. If there were such a link, one would expect that endometriosis of the ovary would lead to endometrioid cancer of the ovary but this is a very rare form of ovarian cancer.

A more likely explanation is that endometriosis is associated with reduced fertility. Women who have never had children are at greater risk to develop ovarian cancer. Each baby reduces a woman's risk of ovarian cancer by twenty percent.

It also must be mentioned here that those women who have undergone hormone treatment for the correction of infertility are NOT at increased risk to develop ovarian cancer. There were a few published papers several years ago suggesting an increased risk in women who took either Clomiphene or Pergonal (or similar drugs). A recent publication clearly showed that there is no increased risk.

It is important that you understand that this is only preliminary data but it is important to keep it in mind - particularly for those women who are contemplating hysterectomy. The decision to remove or conserve at least one ovary must be balanced against the possible increased risk of ovarian cancer. As I have already noted, there is the unknown risk of developing cancer in the endometriosis implants themselves although I believe that time will prove this to be a very rare complication.