by Emily Goebel, MD FRCPC, reviewed on July 27, 2019
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 mucinous carcinoma?
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?
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.
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.
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.
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:
Why is this important? The pattern of invasion is important because infiltrative growth is associated with worse prognosis when compared to expansile growth.
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.
Why is this important? There is no difference in prognosis between these two histologic types.
Grade is a word pathologists use to describe how different cancer cells look compared to 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:
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 cancer 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).
Your pathologist will carefully examine the tissue under the microscope to see if there are any cancer cells on the surface of the ovary.
Why is this important? 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).
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 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.
Why is this important? Cancer cells in other organs are used to determine the tumour stage (see Pathologic stage below).
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.
Why is this important? Cancers of the appendix can look very similar to mucinous carcinoma of the ovary. Cancers that start in the appendix can travel (metastasize) from the appendix to the ovary.
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 (see Lymphovascular invasion above). The movement of cancer cells from the tumour to a lymph node is called a metastasis.
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.
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.
Why is this important? Cancer cells found in a lymph node is 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).
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 a cancer from another organ, such as the appendix, may have traveled (metastasized) 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.
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.
Mucinous carcinoma is given a metastatic stage of 0 or 1 based on the presence of cancer 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.