The article was reviewed on July 27, 2019 by Jason Wasserman, MD PhD FRCPC
The normal ovary
The ovaries are part of the female reproductive tract. The ovaries are small organs that are attached to the uterus by the fallopian tubes. The outer surface of the ovaries are lined by specialized cells called epithelial cells that form a barrier called an epithelium.
What is endometrioid carcinoma?
Endometrioid adenocarcinoma is a type of ovarian cancer. It can start on either on the outer surface of the ovary or within tissue below the surface of the ovary. This cancer is given the name ‘endometrioid’ because when examined under the microscope, the cells in this tumour look similar to the glands normally found in the endometrium of the uterus.
Another type of cancer, also called endometrioid carcinoma starts in the endometrium and can look exactly as endometrioid carcinoma of the ovary when examined under the microscope.
In many cases, patients with endometrioid carcinoma have a history of endometriosis or their ovaries will show evidence of endometriosis. For this reason, it is believed that in some women, endometriosis acts as the ‘seed’ for the development of endometrioid carcinoma in the future. However, the vast majority of women who have endometriosis will never develop endometrioid carcinoma so the risk associated with endometriosis is still quite low.
How do pathologists make this diagnosis?
For most women, the diagnosis of endometrioid carcinoma is only made when the entire tumour has been surgically removed and sent to a pathologist for examination. The fallopian tube and uterus may be removed at the same time.
In some situations, the surgeon will request an intraoperative or frozen section consultation from your pathologist. The diagnosis made by your pathologist during the intraoperative consultation can change the type of surgery performed or the treatment offered after the surgery is completed.
Histologic grade (FIGO grade)
Pathologists use the word grade to describe how different the cancer cells in endometrioid carcinoma look compared to normal endometrial cells.
Because the normal endometrial cells form glands, the grade of endometrioid carcinoma is based on the amount of cancer cells forming glands. Cancer cells that are not forming glands are described as showing a solid pattern of growth which means there is very little space between the cancer cells.
Pathologists divide the grade into three categories based on how the cancer cells look when examined under the microscope.
Why is this important? Grade 3 tumours are associated with worse prognosis compared to lower grade (1 or 2) tumours.
This is the size of the tumour measured in millimeters. The tumour size is only measured after the entire tumour has been removed.
Tumour received intact or ruptured
All ovarian tumours are examined to see if there are any holes or tears in the outer surface of the tumour or ovary. The outer surface is referred to as the capsule. The capsule is described as intact if no holes or tears are identified. The capsule is described as ruptured if the outer surface contains any large holes or tears.
Why is this important? This information is important because a capsule that ruptures inside the body may spill cancer cells into the abdominal cavity. A ruptured capsule is associated with worse prognosis and is used to determine the tumour stage (see Pathologic stage below).
Cancer cells on the surface of the ovary or fallopian tube
The cancer cells in endometrioid carcinoma can spread from the ovary to another nearby organ such as the fallopian tube or the ovary on the other side of the body.
If cancer cells are seen on the surface of the fallopian tube or ovary, it suggests that they have traveled there from another site.
Why is this important? This information is important because a tumour that has spread from one organ to another is given a higher tumour stage (see Pathologic stage below) .
Other organs or tissues involved
Small samples of tissue are commonly removed in a procedure called a biopsy to see if cancer cells have spread to the pelvis or abdomen. These biopsies which are often called omentum or peritoneum are sent for pathological examination along with the tumour.
Other organs (such as bladder, small intestine, or large intestine) are not typically removed and sent for pathological examination unless they are directly attached to the tumour. In these cases your pathologist will examine each organ under the microscope to see if there are any cancer cells attached to those organs.
Why is this important? Cancer cells in other organs are used to determine the tumour stage (see Pathologic stage below).
Lymph nodes are small immune organs located throughout the body. Cancer cells can travel from the tumour to a lymph node through lymphatic channels located in and around the tumour (see Lymphovascular invasion above). The movement of cancer cells from the tumour to a lymph node is called a metastasis.
Your pathologist will carefully examine all lymph nodes for cancer cells. Lymph nodes that contain cancer cells are often called positive while those that do not contain any cancer cells are called negative. Most reports include the total number of lymph nodes examined and the number, if any, that contain cancer cells.
If cancer cells are found in a lymph node, the size of the area involved by cancer will be measured and described in your report.
Why is this important? Cancer cells found in a lymph node is associated with a higher risk that the cancer cells will be found in other lymph nodes or in a distant organ such as the lungs. The number of lymph nodes with cancer cells is also used to determine the nodal stage (see Pathologic stage below).
If you were treated with chemotherapy (or other drugs designed to kill cancer cells) prior to surgical removal of your tumour, your pathologist will examine the tumour to determine the percentage of the tumour that is still alive (viable).
The response will be categorized as follows:
The pathologic stage for endometrioid adenocarcinoma is based on the TNM staging system, an internationally recognized system originally created by the American Joint Committee on Cancer.
This system uses information about the primary tumour (T), lymph nodes (N), and distant metastatic disease (M) to determine the complete pathologic stage (pTNM). Your pathologist will examine the tissue submitted and give each part a number. In general, a higher number means more advanced disease and worse prognosis.
Tumour stage (pT)
Nodal stage (pN)
Metastatic stage (pM)
Endometrioid carcinoma is given a metastatic stage between 0 and 1 based on the presence of cancer cells at a distant site in the body (for example the lungs). The metastatic stage can only be determined if tissue from a distant site is submitted for pathological examination.
Mismatch repair testing
Each cell in your body contains a set of instructions that tell the cell how to behave. These instructions are written in a language called DNA and the instructions are stored on 46 chromosomes in each cell. Because the instructions are very long, they are broken up into sections called genes and each gene tells the cell how to produce piece of the machine called a protein.
If the DNA becomes damaged or if it cannot be read accurately, the cell will be unable to produce the proteins it requires to function normally. An area of damaged DNA is called a mutation and mutations are one of the most common causes of cancer in humans.
For most patients, endometrioid carcinoma arises as a result of both environmental factors and genetic factors. These tumours are said to be ‘sporadic’ because they cannot be totally predicted.
Some patients, however, inherit particular genes that put them at a much higher risk for developing endometrioid carcinoma. These people are said to have a syndrome and the most common syndrome associated with endometrial carcinoma is called Lynch.
Lynch syndrome is caused by the loss of one of 4 special proteins (MSH2, MSH6, MLH1, and PMS2) that normally function to remove errors from the genetic material (DNA) in your cells. When one of these proteins is lost, mutations start to accumulate and the normal cell can eventually turn into cancer.
As a precaution, pathologists test all endometrioid carcinomas for Lynch syndrome using a test called mismatch repair. This test looks at the activity of MSH2, MSH6, MLH1, and PMS2 and if one or more of them is lost, additional testing may be performed to assess your risk for Lynch syndrome.
Why is this important? The diagnosis of Lynch syndrome is important not only for the patient but also for the patient’s family who may also be at risk of cancer as a result of the syndrome.