Endometrioid carcinoma of the ovary

by Sandra Lee MD FRCPC
October 15, 2022

What is endometrioid carcinoma of the ovary?

Endometrioid carcinoma is a type of ovarian cancer. Most endometrioid carcinomas are associated with a condition called endometriosis. Endometriosis is the presence of endometrial tissue (which is normally found in the uterus) outside of the uterus and the ovary is a common location to find endometriosis. About 1% of patients with endometriosis will develop a tumour related to their endometriosis and these tumours most commonly occur in the ovary. A similar tumour, also called endometrioid carcinoma, can be found in the uterus.

How is the diagnosis of endometrioid carcinoma of the ovary made?

For most women, the diagnosis of ovarian endometrioid carcinoma of the ovary is only made when the entire tumour has been surgically removed and sent to a pathologist for examination.

What is an intraoperative consultation (frozen section)?

An intraoperative consultation is an opportunity for your surgeon and pathologist to examine the tumour, lymph nodes, or other tissue samples at the time of surgery. During this consultation, a frozen section may be performed where the tissue is quickly examined under the microscope. The purpose of an intraoperative consultation and frozen section is to provide your surgeon with information that will help guide decisions made at the time of surgery.

How do pathologists determine the FIGO grade for endometrioid carcinoma of the ovary?

Pathologists divide endometrioid carcinoma of the ovary into three grades based on the percentage of tumour cells forming round structures called glands. Tumour cells that are not forming glands are described as showing a solid pattern of growth which means there is very little space between the tumour cells. In addition, the grade will be increased by one point if the nucleus (the part of the cell that holds the genetic material) in the majority of tumour cells is very abnormal-looking. Pathologists describe this as severe nuclear atypia. The FIGO grade is important because grade 3 tumours are associated with a worse prognosis compared to lower grade (1 or 2) tumours.

Using these criteria, pathologists divide the FIGO grade into three categories:

• Grade 1 – Most of the tumour is forming glands. The tumour shows less than a 5% solid pattern of growth.
• Grade 2 – Some of the tumour is forming glands. The tumour shows a 6 to 50% solid pattern of growth.
• Grade 3 – Very few glands are seen. The tumour shows a more than 50% solid pattern of growth.

Were tumour cells seen on the surface of the ovary or fallopian tube?

The tumour 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 tumour cells are seen on the surface of the fallopian tube or ovary, it suggests that they have spread there from the tumour. The spread of cells from the tumour to another body site is called metastasis. This information is important because a tumour that has spread or metastasized from one organ to another is given a higher tumour (T) stage.

Why is it important if the tumour was received intact or ruptured?

All ovarian tumours are examined to see if there are any holes or tears in the outer (capsular) surface of the ovary. The capsular surface is described as intact if no holes or tears are identified. The capsular surface is described as ruptured if it contains any large holes or tears. If the ovary or tumour is received in multiple pieces, it may not be possible for your pathologist to tell if the capsular surface has ruptured or not. This information is important because a capsular surface that ruptures inside the body may spill tumour cells into the abdominal cavity. A ruptured capsule is associated with a worse prognosis and is used to determine the tumour (T) stage.

Has the tumour spread to other organs or tissues in the pelvis or abdomen?

Small samples of tissue are commonly removed in a procedure called a biopsy to see if tumour cells have spread outside of the ovary. These biopsies, which are often from a tissue in the pelvis and abdomen called the peritoneum, are sent to your pathologist to see if the tumour has spread or metastasized. The omentum is an abdominal organ that is a common site of tumour spread or metastasis. This organ is often entirely removed and examined by your pathologist. Other organs (such as the bladder, small intestine, or large intestine) are not typically removed and sent for pathological examination unless they are directly attached to the tumour or tumour spread to these organs is seen by your surgeon. In these cases, your pathologist will examine each organ under the microscope to see if there are any cancer cells attached to those organs. The presence of tumour cells in other organs is used to determine the tumour (T) stage and distant metastatic disease (M) stage.

Were lymph nodes examined and did any contain cancer cells?

Lymph nodes are small immune organs found throughout the body. Cancer cells can spread from a tumour to lymph nodes through small vessels called lymphatics. For this reason, lymph nodes are commonly removed and examined under a microscope to look for cancer cells. The movement of cancer cells from the tumour to another part of the body such as a lymph node is called a metastasis.

Cancer cells typically spread first to lymph nodes close to the tumour although lymph nodes far away from the tumour can also be involved. For this reason, the first lymph nodes removed are usually close to the tumour. Lymph nodes further away from the tumour are only typically removed if they are enlarged and there is a high clinical suspicion that there may be cancer cells in the lymph node.

If any lymph nodes were removed from your body, they will be examined under the microscope by a pathologist and the results of this examination will be described in your report. Most reports will include the total number of lymph nodes examined, where in the body the lymph nodes were found, and the number (if any) that contain cancer cells. If cancer cells were seen in a lymph node, the size of the largest group of cancer cells (often described as “focus” or “deposit”) will also be included.

The examination of lymph nodes is important for two reasons. First, this information is used to determine the pathologic nodal stage (pN). Second, finding cancer cells in a lymph node increases the risk that cancer cells will be found in other parts of the body in the future. As a result, your doctor will use this information when deciding if additional treatment such as chemotherapy, radiation therapy, or immunotherapy is required.

What does it mean if a lymph node is described as positive?

Pathologists often use the term “positive” to describe a lymph node that contains cancer cells. For example, a lymph node that contains cancer cells may be called “positive for malignancy” or “positive for metastatic carcinoma”.

What does it mean if a lymph node is described as negative?

Pathologists often use the term “negative” to describe a lymph node that does not contain any cancer cells. For example, a lymph node that does not contain cancer cells may be called “negative for malignancy” or “negative for metastatic carcinoma”.

What are isolated tumour cells (ITCs)?

Pathologists use the term ‘isolated tumour cells’ to describe a group of tumour cells that measures 0.2 mm or less and is found in a lymph node. Lymph nodes with only isolated tumour cells (ITCs) are not counted as being ‘positive’ for the purpose of the pathologic nodal stage (pN).

What is a micrometastasis?

A ‘micrometastasis’ is a group of tumour cells that measures from 0.2 mm to 2 mm and is found in a lymph node. If only micrometastases are found in all the lymph nodes examined, the pathologic nodal stage is pN1mi.

What is a macrometastasis?

A ‘macrometastasis’ is a group of tumour cells that measures more than 2 mm and is found in a lymph node. Macrometastases are associated with a worse prognosis and may require additional treatment.

What does extranodal extension mean?

All lymph nodes are surrounded by a thin layer of tissue called a capsule. Extranodal extension means that cancer cells within the lymph node have broken through the capsule and have spread into the tissue outside of the lymph node. Extranodal extension is important because it increases the risk that the tumour will regrow in the same location after surgery. For some types of cancer, extranodal extension is also a reason to consider additional treatment such as chemotherapy or radiation therapy.

What is mismatch repair testing and why is it performed?

​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. The instructions are broken up into sections called genes and each gene tells the cell how to produce a protein. Proteins allow cells to live and to work properly.

If the DNA becomes damaged or if it cannot be read accurately, the cell will be unable to produce normal proteins and the cell may not function normally. An area of damaged DNA is called a mutation and mutations are one of the most common causes of cancer in humans.

When DNA becomes damaged, there are proteins that try to fix the damaged areas/mutations. Mismatch repair proteins are a set of proteins that normally function to remove certain types of damage/mutations from the DNA in your cells. The four main mismatch repair proteins are MLH1, PMS2, MSH2, and MSH6. When one of these proteins does not work properly, mutations in other genes can start to accumulate and a normal cell can eventually turn into a cancer cell. Pathologists can test the mismatch repair proteins to see if they are working properly. If one or more of the mismatch repair proteins is not working properly this is called mismatch repair deficiency.

In most tumours, mismatch repair deficiency is somatic, which means the mutation is only present in your tumour cells. Somatic mutations can result from both environmental and complex genetic factors, and it is very difficult to determine the exact reason why the mismatch repair protein stopped working properly.

Sometimes mismatch repair protein mutations are inherited. Inherited mutations are also called germline mutations. Germline mutations are mutations that are present in all of the cells in your body as well as your tumour cells. They can be passed down/inherited from your parents and they can also be passed down/inherited to your children. A person who inherits a mismatch repair protein that does not work properly has a higher risk of developing certain cancers and is said to have a cancer syndrome called Lynch syndrome.

In ovarian endometrioid carcinomas, mismatch repair deficiency occurs in a small percentage of cases (about 13%). Most of these are due to somatic mismatch repair protein mutations. A small number of ovarian endometrioid carcinomas with mismatch repair deficiency are related to germline mismatch repair protein mutations (Lynch syndrome). In some hospitals, ovarian endometrioid carcinomas are tested by your pathologist for mismatch repair deficiency. If mismatch repair deficiency is identified in your tumour, additional testing may be done to assess your risk for Lynch syndrome.

Because Lynch syndrome results from an inherited gene mutation, the diagnosis of Lynch syndrome is important not only for you but also for your family. If additional testing confirms you have Lynch syndrome, your family members may want to have additional testing to see if they also have Lynch syndrome.