Mucinous borderline tumour - Ovary -

This article will help you read and understand your pathology report for mucinous borderline tumour of the ovary.

by Emily Goebel, MD FRCPC, updated on November 7, 2018

Quick facts:
  • Mucinous borderline tumour is a type of non-cancerous ovarian tumour.
  • Although the tumour is non-cancerous, there is a small risk that this tumour can turn into a cancer over time.
  • Pathologists carefully examine these tumours under the microscope for any evidence of cancer.
The anatomy of the 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.

Gynecological tract


What is a mucinous borderline tumour?

A mucinous borderline tumour is a non-cancerous tumour but it is associated with a small risk of turning into cancer over time. 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.

When the tumour is examined under the microscope, the tissue on the inside of the cysts and the solid areas are made up of an abnormal type of epithelium that forms glands and produces a thick, gelatinous fluid called mucin. The mucin fills the inside of the tumour.

The behavior of this tumour is thought to fall somewhere in between a mucinous cystadenoma which is a non-cancerous tumour and mucinous carcinoma which is a type of cancer.

How do pathologists make this diagnosis?

For most women, the diagnosis of mucinous 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.​

Cancer in a mucinous borderline tumour

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

  1. Intraepithelial carcinoma – These are groups of very abnormal tumour cells that look different from the rest of the tumour. These cells have changed into cancer cells.
  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? Intraepithelial carcinoma and microinvasion are early signs of cancer and both are associated with worse prognosis.

Histologic type

There are two types of mucinous borderline tumour and the type depends on the kinds of cells seen in the mucin producing epithelium when the tumour is examined under the microscope.

  1. Endocervical – In this type of tumour the cells in the epithelium look similar to the cells that line the endocervical canal (the canal that leads from the cervix into the uterus).
  2. Intestinal – In this type of tumour the cells in the epithelium look similar to the cells that line the digestive (intestinal) tract.  The intestinal type is more common than the endocervical type.

There is no difference in prognosis between these two types.

Intact or ruptured tumour

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.

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.

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 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.

Tumour cells in other organs are used to determine the tumour stage (see Pathologic stage below).​

The appendix

If you have been diagnosed with mucinous borderline or if your doctor suspects you may have a mucin producing tumour, your appendix might also be removed and sent for pathological examination. In these cases, your pathologist will examine the appendix for any tumour cells.

Tumours of the appendix can look very similar to mucinous borderline of the ovary. Tumours that start in the appendix can travel (metastasize) from the appendix to the ovary.

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.

Since the risk of tumour cells traveling to a lymph node is very low for mucinous tumours, lymph nodes are not usually removed at the time of surgery.

Pathologic stage

​The pathologic stage for mucinous 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)

Mucinous 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.

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