Ovary and fallopian tube -

Serous borderline tumour

This article was last reviewed and updated on July 29, 2019
by Emily Goebel, MD FRCPC

Quick facts:

  • Serous borderline tumour is a type of non-cancerous ovarian tumour.

  • Although the tumour is non-cancerous, it is associated with a small risk of turning into a cancer over time.

  • Pathologists carefully examine these tumours under the microscope for any evidence of cancer.

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 serous borderline tumour?

Serous borderline tumours are tumours of low malignant potential which means that they have a small risk of turning into cancer.


Their behavior of a serous borderline tumour is thought to fall in between a serous cystadenoma which is a non-cancerous (benign) tumour and low grade serous carcinoma which is a type of cancer (a malignant tumour).

How do pathologists make this diagnosis?

Serous borderline tumours develop from the epithelial cells on the outer surface of the ovary. The tumour is usually made up of many small spaces. Pathologists call these spaces cysts. The walls of the cysts can be thin or thick and more solid areas may be found inside some of the cysts. Pathologists sometimes call these solid areas excrescences.


The inside of the cysts are lined by a type of cell called serous cells. These cells produce a clear fluid which fills the inside of the tumour. The cysts with thick walls and the solid areas may have small finger like projections of tissue. Pathologists call these projections papillary


Why is this important? The more solid areas and papillary projections are what make a serous borderline tumour different from a serous cystadenoma.

Your pathologist will carefully examine the tumour under the microscope for two microscopic features that will help determine your prognosis.


  1. Micropapillary growth - These are small groups of cells that have started to grow in a pattern that is different from the rest of the tumour. Tumour cells that grown in a micropapillary pattern are more likely to spread to other parts of the body.

  2. Microinvasion - These are single tumour cells that have moved out of the epithelium and into the stroma below. The movement of tumour cells into the stroma is called invasion. Invasion is something that happens when the tumour changes in a cancer.


Why is this important? Micropapillary growth and microinvasion are early signs of cancer and both are associated with worse prognosis.


For most women, the diagnosis of serous 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).

Peritoneal implants

The organs inside the abdomen are lined by a thin layer of tissue called the peritoneum. Your pathologist will carefully examine any tissue from the peritoneum to look for tumour cells. Tumour cells in the peritoneum are called implants.  


There are two kinds of implants.

  1. Non-invasive implants - The cells are sitting on the surface of the peritoneum.  This type of implant is not associated with worse prognosis.

  2. Invasive implants - These cells have pushed their way below the surface of the peritoneum. This process is called invasion. Invasive implants are associated with worse prognosis and is now considered the same as low-grade serous carcinoma.


Why is this important? The presence of peritoneal implants is used to determine the tumour stage (see Pathologic stage below) and invasive implants are associated with worse prognosis.

Other organs or tissues involved

Small samples of tissue are commonly 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


The tumour cells from a serous borderline tumour can travel (metastasize) to lymph nodes. If tumour cells are found in a lymph node it will be described in your pathology report.


Why is this important? Unlike other types of tumours, tumour cells from a serous borderline tumour found in a lymph node are not associated with worse prognosis.

Pathologic stage

​The pathologic stage for serous 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 tumour 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)

Serous borderline tumour 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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