Endometrioid carcinoma of the uterus

by Jason Wasserman MD PhD FRCPC
May 28, 2022


About this article: This article was created by doctors to help you read and understand your pathology report for endometrioid carcinoma of the uterus. If you have any questions about this article or your pathology report, please contact us.

What is endometrioid carcinoma of the uterus?

Endometrioid carcinoma of the uterus is a type of endometrial cancer. It starts in the endometrium, a thin layer of tissue that covers the inside of the uterus. It is the most common type of endometrial cancer among adult women. A similar tumour, also called endometrioid carcinoma, can be found in the ovary.

Gynecological tract

Which precancerous conditions are associated with endometrioid carcinoma of the uterus?

Endometrioid carcinoma of the uterus is believed to develop from a pre-cancerous condition called atypical endometrial hyperplasia.

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

Endometrioid carcinoma of the uterus is usually diagnosed after a small sample of tissue is taken from the endometrium in a procedure called a biopsy or curettage. After the diagnosis, the tumour is removed in a surgical procedure called a hysterectomy.​

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

Pathologists divide endometrioid carcinoma of the uterus 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.
What does myometrial invasion mean and why is it important?

All endometrioid carcinomas start from a layer of tissue on the inside of the uterus called the endometrium. The myometrium is a thick band of muscle just below the endometrium. The movement of tumour cells from the endometrium into the myometrium is called myometrial invasion. The amount of myometrial invasion will be described in millimetres and as a percentage of the total myometrial thickness. Myometrial invasion is an important prognostic factor and is used to determine the tumour stage (see Pathological stage below).

What is the cervical stroma and why is it important?

The cervix is a structure at the very bottom of the uterus. The cervix connects directly with the endometrium. The wall of the cervix is made up of a type of tissue called the stroma. Endometrioid carcinoma may grow from the endometrium into the cervix. After the tumour is removed completely, your pathologist will carefully examine the tissue from the cervix to see if there are any tumour cells in the cervical stroma. This examination is important because finding tumour cells in the cervical stroma increases the tumour stage (see Pathologic stage below).

Has the tumour grown into any other organs outside of the uterus?

Several other organs are directly attached or are very close to the uterus including the ovaries, fallopian tubes, vagina, bladder, and rectum. A tumour that spreads directly into any of these organs is associated with a poor prognosis and will be described in your report.

What is lymphovascular invasion?

Blood moves around the body through long thin tubes called blood vessels. Another type of fluid called lymph which contains waste and immune cells moves around the body through lymphatic channels. The term lymphovascular invasion is used to describe tumour cells that are found inside a blood vessel or lymphatic channel. Lymphovascular invasion is important because once the tumour cells are inside a blood vessel or lymphatic channel they are able to metastasize (spread) to other parts of the body such as lymph nodes or the lungs.

lymphovascular invasion

What is a margin?

A margin is the normal tissue that surrounds a tumour and is removed with the tumour at the time of surgery. The margins will only be described in cases where the tumour extends into the cervical stroma or other tissues surrounding the uterus and after the entire tumour has been removed.

A margin is called positive when there are tumour cells at the very edge of the cut tissue. A positive margin is associated with a higher risk that the tumour will recur in the same site after treatment. A negative margin means that no tumour cells were seen at any of the cut edges of tissue.

Margin

What are lymph nodes?

Lymph nodes are small immune organs located throughout the body. Tumour 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 tumour cells from the tumour to a lymph node is called metastasis.

Your pathologist will carefully examine each lymph node for tumour cells. Lymph nodes that contain tumour cells are often called positive while those that do not contain any tumour cells are called negative. Most reports include the total number of lymph nodes examined and the number, if any, that contain tumour cells.

Lymph nodes on the same side as the tumour are called ipsilateral while those on the opposite side of the tumour are called contralateral. Lymph nodes examined are usually divided into those found in the pelvis and those found around a large blood vessel in the abdomen called the aorta. The lymph nodes found around the aorta are called para-aortic.

If tumour cells are found in a lymph node, the size of the area involved by the tumour will be measured and described in your report.

  • Isolated tumour cells – The area inside the lymph node with tumour cells is less than 0.2 millimetres in size.
  • Micrometastases – The area inside the lymph node with tumour cells is more than 0.2 millimetres but less than 2 millimetres in size.
  • Macrometastases – The area inside the lymph node with tumour cells is more than 2 millimetres in size.

Lymph node

What are mismatch repair proteins?

Mismatch repair (MMR) is a system inside all normal, healthy cells for fixing mistakes in our genetic material (DNA). The system is made up of different proteins and the four most common are called MSH2, MSH6, MLH1, and PMS2.

The four mismatch repair proteins MSH2, MSH6, MLH1, and PMS2 work in pairs to fix damaged DNA. Specifically, MSH2 works with MSH6 and MLH1 works with PMS2. If one protein is lost, the pair cannot function normally. A loss of one of these proteins increases the risk of developing cancer.

Pathologists order mismatch repair testing to see if any of these proteins are lost in a tumour. If mismatch repair testing has been ordered on your tissue sample, the results will be described in your pathology report.

How do pathologists test for mismatch repair proteins?

The most common way to test for mismatch repair proteins is to perform a test called immunohistochemistry. This test allows pathologists to see if the tumour cells are producing all four mismatch repair proteins.

If the tumour cells are not producing one of the proteins, your report will describe this protein as “lost” or “deficient”. Because the mismatch repair proteins work in pairs (MSH2 + MSH6 and MLH1 + PMS2), two proteins are often lost at the same time.

If the tumour cells in your tissue sample show a loss of one or more mismatch repair proteins, you may have inherited Lynch syndrome and should be referred to a genetic specialist for additional tests and advice.

How do pathologists determine the pathologic stage (pTNM) for endometrioid carcinoma of the uterus?​

​The pathologic stage for endometrioid carcinoma 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 a worse prognosis.

Tumour stage (pT)

Endometrioid carcinoma is given a tumour stage between 1 and 4 based on the depth of myometrial invasion and growth of the tumour outside of the uterus.

  • T1 – The tumour only involves the uterus.
  • T2 – The tumour has grown to involve the cervical stroma.
  • T3 – The tumour has grown through the wall of the uterus and is now on the outer surface of the uterus OR it has grown to involve the fallopian tubes or ovaries.
  • T4 – The tumour has grown directly into the bladder or the colon.
Nodal stage (pN)

Endometrioid carcinoma is given a nodal stage from 0 to 2 based on the examination of lymph nodes from the pelvis and abdomen.

  • N0 – No tumour cells were found in any of the lymph nodes examined.
  • N1mi – Tumour cells were found in at least one lymph node from the pelvis but the area with cancer cells was not larger than 2 millimetres (only isolated tumour cells or micrometastasis).
  • N1a – Tumour cells were found in at least one lymph node from the pelvis and the area with cancer cells was greater than 2 millimetres (macrometastasis).
  • N2mi – Tumour cells were found in at least one lymph node outside the pelvis but the area with cancer cells was not larger than 2 millimetres (only isolated tumour cells or micrometastasis).
  • N2a – Tumour cells were found in at least one lymph node outside the pelvis and the area with cancer cells was greater than 2 millimetres (macrometastasis).
  • NX – No lymph nodes were sent for examination.
Metastatic stage (pM)

Endometrioid carcinoma is given a metastatic stage of 0 or 1 based on the presence of tumour 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. Because this tissue is rarely present, the metastatic stage cannot be determined and is listed as MX.

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