Your diagnosis

Mucinous carcinoma of the ovary

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

by Emily Goebel MD FRCPC, updated April 20, 2021

Quick facts:
  • Mucinous carcinoma is a type of ovarian cancer.
  • These tumours can become quite large before they cause any symptoms.
  • Your pathology report for mucinous carcinoma will include important information such as the pattern of growth and the tumour grade.
The ovary

The ovaries are part of the female reproductive tract. The ovaries are small organs that are attached to the uterus by the fallopian tubes. The outer surface of the ovaries are lined by specialized cells called epithelial cells that form a barrier called an epithelium. The tissue below the epithelium is called the stroma.

Gynecological tract

What is mucinous carcinoma of the ovary?

Mucinous carcinoma is a type of ovarian cancer. It develops from the tissue on the inside 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.

How do pathologists make this diagnosis?

For most women, the diagnosis of mucinous carcinoma 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.

Your surgeon may 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.​

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.

In some cases, this cancer develops from a pre-existing mucinous borderline tumour. If your pathologist also sees a mucinous borderline tumour, it will be described in your report.

Your pathologist will carefully examine the tumour under the microscope for features that will help determine your prognosis. All mucinous carcinomas start in the epithelium and the movement of cancer cells into the stroma is called invasion.

Pattern of growth

The pattern of growth describes the way the cancer cells spread into the surrounding normal stroma. After examining your tissue sample under the microscope, your pathologist will describe the pattern of growth as one of the following:

  1. Infiltrative growth – In this pattern, single cancer cells or irregularly shaped glands are seen spreading into the stroma.
  2. Expansile growth – In this pattern, the cancer cells are pushing into the stroma as a large group.

The pattern of invasion is important because infiltrative growth is associated with a worse prognosis when compared to expansile growth.

Histologic type

There are two types of mucinous carcinoma and the type depends on the kinds of cells seen in the mucinous 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 histologic types.

Histologic grade

Grade is a word pathologists use to describe how different cancer cells look compared to the normal mucinous epithelium.  Because in other parts of the body, normal mucinous epithelium forms glands, mucinous carcinoma is divided into 3 grades based on how much of the tumour is made up of glands:

  1. Well differentiated – The cancer cells mostly form glands, with only a small percentage of the cancer cells growing in a solid pattern.
  2. Moderately differentiated – Some glands are still seen.
  3. Poorly differentiated – The cancer cells are growing mostly in a solid pattern with very few glands.
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 cancer cells into the abdominal cavity. A ruptured capsule is associated with a 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 cancer cells on the surface of the ovary. Cancer 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 cancer 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 the 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 cancer cells attached to those organs.

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

The appendix

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

Cancers of the appendix can look very similar to mucinous carcinoma of the ovary. Cancers that start in the appendix can spread from the appendix to the ovary.

Lymph nodes

Lymph nodes are small immune organs located throughout the body. Cancer cells can travel from the tumour to a lymph node through lymphatic channels located in and around the tumour. The movement of cancer cells from the tumour to a lymph node is called metastasis.

Lymph node

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

Normal lymphatics of pelvis

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

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

Cancer cells found in a lymph node are associated with a higher risk that the cancer cells will be found in other lymph nodes or in a distant organ such as the lungs. The number of lymph nodes with cancer cells is also used to determine the nodal stage (see Pathologic stage below).

Immunohistochemistry

Some cancers, such as those from the appendix, may look very similar to mucinous carcinoma from the ovary. For that reason, your pathologist may perform a test called immunohistochemistry to help confirm the diagnosis of mucinous carcinoma and rule out the possibility that cancer from another organ, such as the appendix, may have spread to the ovary.

Mucinous carcinomas of the ovary may be positive or reactive for immunohistochemical markers such as PAX8, CK7, CK20 and CDX2 and negative or non-reactive for SATB2, which you may see included in your pathology report.

Pathologic stage

​The pathologic stage for mucinous 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 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)
ovary cancer T1 T2 T3Nodal stage (pN)

Node stage ovary cancer

Metastatic stage (pM)

ovary cancer M stage

A+ A A-