Ovary and fallopian tube -

Endometrioid borderline tumour

This article was last reviewed and updated on July 27, 2019
by Emily Goebel, MD FRCPC

Quick facts:

  • Endometrioid borderline tumour is a type of ovarian tumour.

  • It is a non-cancerous tumour although it does have a small risk of turning into a cancer called endometrioid adenocarcinoma if left untreated.


The normal ovary

The ovaries are part of the female reproductive tract. They are small organs that are attached to the uterus by the fallopian tubes. The outer surface of the ovaries are lined by a thin layer of specialized tissue called an epithelium that forms a barrier around the outside of the ovary.


The organs inside the abdomen are lined by a thin layer of tissue called the peritoneum that is made up of similar cells. The ovaries also contain large cells called eggs. The tissue below the epithelium is called stroma.

What is an endometrioid borderline tumour?

Endometrioid borderline tumours are tumours of low malignant potential which means that they have a small risk of turning into cancer. The behaviour of a borderline tumour is in between that of an endometrioid cystadenofibroma which is a non-cancerous (benign) tumour and endometrioid adenocarcinoma which is a type of cancer.  


Endometrioid borderline tumours can start either on the outer surface of the ovary or within tissue below the surface of the ovary.
In many cases, patients with endometrioid borderline tumours 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 borderline tumours or endometrioid adenocarcinoma in the future. However, the vast majority of women who have endometriosis will never develop endometrioid borderline tumours or endometrioid adenocarcinoma, so the risk associated with endometriosis is still quite low.

How does a pathologist make this diagnosis?

Under the microscope these tumours are made up of crowded glands lined by abnormal cells. The cells in an endometrioid borderline tumour look similar to the cells that normally line the endometrial cavity of the uterus which is why they are called endometrioid (meaning "like" the endometrium).  

Your pathologist will carefully examine the tumour for single tumour cells or irregular glands that have moved out of the epithelium and into the stroma below. The movement of tumour cells into the stroma is called invasion and tumours with this feature are called endometrioid borderline tumours with microinvasion.  


Why is this important? Microinvasion is important because it is associated with a higher risk of recurrence and worse prognosis. If this feature is seen it will be described in your report. 

For most women, the diagnosis of endometrioid borderline tumour 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.​

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 tumour 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).

Ovarian surface involvement

Your pathologist will carefully examine the tissue under the microscope to see if there are any tumour cells on the surface of the ovary.


Why is this important? Tumour cells on the surface of the ovary increase the risk that the tumour will spread to other organs in the pelvis or abdomen. It is also used to determine the tumour stage (see Pathologic stage below).

Other organs or tissues involved

Small samples of tissue may be removed in a procedure called a biopsy to see if tumour 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 tumour cells attached to those organs.

Why is this important? Tumour cells in other organs are used to determine the tumour stage (see Pathologic stage below).​

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 a metastasis

Your pathologist will carefully examine all lymph nodes 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.

Since the risk of lymph node involvement is low for endometrioid borderline tumours, in many cases lymph nodes are not removed at the time of surgery. 

Pathologic stage

​The pathologic stage for endometrioid borderline tumour 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.


Pathologic stage is not reported on a biopsy specimen. It is only reported when the entire tumour has been removed in an excision or resection specimen.


Tumour stage (pT)

  • T0 - After careful examination of the tissue, no primary tumour is found. This can happen if you received treatment (for example chemotherapy) before surgery and the tumour shows complete response (see Treatment effect above).

  • T1a - The tumour is found only in one ovary or fallopian tube.

  • T1b - The tumour is found in both ovaries or fallopian tubes.

  • T1c - The tumour is found in only one ovary or fallopian tube but the tumour capsule is broken OR tumour cells were found in fluid taken out of the abdomen or pelvis.

  • T2a - The tumour extends to the uterus or cancer cells were found on the surface of the ovaries, fallopian tubes, or uterus (implants).

  • T2b - The tumour extends to other parts of the pelvis or tumour cells were found on the surface of tissues in the pelvis (implants).

  • T3 - Tumour cells are found outside of the pelvis in the tissues of the abdomen.

Nodal stage (pN)

  • NX - No lymph nodes were sent to pathology for examination.

  • N0 - No tumour cells are found in any of the lymph nodes examined.

  • N0(i+) -Only isolated tumour cells are found in a lymph node (see Lymph nodes above).

  • N1a - Tumour cells are found in a lymph node but the area with tumour cells is not greater than 10 millimeters.

  • N1b - Tumour cells are found in a lymph node and the area with tumour cells is greater than 10 millimeters.

Metastatic stage (pM)

Endometrioid borderline tumour is given a metastatic stage between 0 and 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 sent for pathological examination.

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