Mucinous carcinoma of the ovary

By Jason Wasserman MD PhD FRCPC
August 24, 2025

Mucinous carcinoma is a rare type of ovarian cancer. It is made up of tumour cells that look similar to the cells normally found in the gastrointestinal tract, such as the stomach or intestines. These tumour cells produce mucus, which is a thick fluid, and this gives the tumour its name.

Most mucinous carcinomas are found only in the ovary at the time of diagnosis. Advanced disease, where the tumour has spread beyond the ovary, is uncommon.

What are the symptoms of mucinous carcinoma of the ovary?

The most common symptom is a pelvic mass, which may be felt as abdominal bloating, pressure, or pain. Some patients notice changes in bowel or bladder habits or feel full after eating only a small amount of food. Because these tumours can grow very large, they may also cause visible abdominal swelling.

Who gets mucinous carcinoma of the ovary?

The average age at diagnosis is about 55 years. This tumour accounts for about 3 to 4 percent of all primary ovarian cancers in North America. It is more common in parts of Asia, including Indonesia, Singapore, and South Korea.

What causes mucinous carcinoma of the ovary?

The exact cause is not known. However, many mucinous carcinomas develop from a pre-existing tumour called a mucinous borderline tumour. Others may arise from different ovarian tumours such as mature cystic teratomas or Brenner tumours.

At the genetic level, several common changes are seen in these tumours:

• CDKN2A loss: This genetic change is found in about three-quarters of cases. It disrupts a gene that normally helps control cell growth.

• KRAS mutations: Found in about two-thirds of cases, this change causes cells to grow more quickly than normal.

• TP53 mutations: Also seen in about two-thirds of cases, these are linked to progression from borderline tumours to invasive carcinoma.

• ERBB2 (HER2) amplification: Seen in about 15 to 25 percent of cases, this change leads to increased activity of a growth-related protein.

These genetic changes explain how normal ovarian cells or pre-existing tumours can transform into mucinous carcinoma.

How is this diagnosis

The diagnosis is usually made after the tumour has been surgically removed and examined by a pathologist under the microscope. Sometimes, a small piece of the tumour may be sampled with a biopsy, but most cases are diagnosed after surgery.

What is an intraoperative consultation (frozen section)?

During surgery, your surgeon may ask a pathologist to examine the tumour right away to help guide treatment. This is called an intraoperative consultation. A frozen section may be performed, which involves quickly freezing a piece of tissue so it can be examined under the microscope. The pathologist provides a rapid preliminary diagnosis that helps the surgeon decide how much tissue should be removed. The final diagnosis is always made after the tissue is processed more carefully after surgery.

What does mucinous carcinoma look like under the microscope?

Under the microscope, pathologists often see a mixture of benign, borderline, and cancerous areas within the same tumour.

Cancerous areas can show two patterns of invasion:

• Expansile (confluent) invasion: In this pattern, the tumour cells grow together in crowded glands with very little supporting tissue between them. This gives the tumour a maze-like appearance. This type of invasion is more common and usually linked to a better prognosis.

• Infiltrative (destructive) invasion: In this pattern, the tumour cells break away into irregular groups, nests, or single cells. They grow into the surrounding supporting tissue and are often associated with scarring and inflammation. This pattern is less common but is linked to a worse prognosis.

If the tumour shows an infiltrative pattern, especially if both ovaries are involved, pathologists also consider whether the tumour may have spread from another organ, such as the gastrointestinal tract.

What additional tests may be performed to confirm the diagnosis?

Pathologists often perform immunohistochemistry (IHC), a test that uses special stains to look for proteins in the tumour cells. The pattern of proteins can help confirm that the tumour is primary to the ovary rather than a spread from another organ.

Typical results for mucinous carcinoma of the ovary include:

• CK7: Usually positive. This supports an ovarian origin.

• CK20, CEA, and CDX2: May be positive. These proteins are also found in gastrointestinal tumours, so the results must be interpreted carefully.

• CA19-9: Often positive.

• CA125, WT1, ER, and PR: Usually negative. This helps distinguish mucinous carcinoma from other types of ovarian cancer.

• PAX8: Sometimes weakly positive. This supports but does not prove an ovarian origin.

• p53: May show a normal (wild-type) or abnormal (mutated) pattern.

• SATB2: Strong positivity may be seen in tumours that develop from teratomas.

How do pathologists grade mucinous carcinoma of the ovary?

Grading is a way pathologists describe how aggressive a tumour looks under the microscope. It is based on how much the cancer cells differ from normal cells and how quickly they appear to be growing. The grade provides important information about prognosis (the expected outcome) and may influence treatment decisions.

The Silverberg grading system

The Silverberg system is the most widely used and has been shown to predict prognosis in mucinous carcinoma. It uses three features of the tumour:

• Architecture: This describes how the tumour cells are arranged. Tumours that mostly form glands are given a lower score, while those that form solid sheets of cells are given a higher score.

• Nuclear atypia: This refers to how abnormal the cell nuclei (the part of the cell that contains DNA) look. Mildly abnormal nuclei are scored lower, while very irregular nuclei are scored higher.

• Mitotic activity: This measures how many cells are actively dividing. Fewer dividing cells get a lower score, while many dividing cells get a higher score.

The scores for these three features are added together to give a total. The total determines the grade:

• Grade 1 (well differentiated): Tumours look more like normal mucinous epithelium, form glands, and show only mild changes.

• Grade 2 (moderately differentiated): Tumours show more abnormalities in how the cells look and grow, with fewer glands and more solid growth.

• Grade 3 (poorly differentiated): Tumours look very abnormal, form few or no glands, and have many dividing cells. These tumours tend to behave more aggressively.

The growth pattern system

Another way pathologists describe mucinous carcinoma is by looking at the growth pattern of the tumour. This system divides tumours into two broad categories:

• Low grade: Tumours grow in an expansile or confluent pattern. This means the tumour grows as a large, pushing mass, or has at most 10% of an infiltrative pattern. These tumours are generally associated with a better prognosis.

• High grade: Tumours show an infiltrative pattern in more than 10% of the tumour. Infiltrative growth means the cancer cells invade into the surrounding tissue in small, irregular clusters. This pattern is linked with a higher risk of recurrence and worse outcomes.

Why is it important if the tumour was received intact or ruptured?

The outer layer of the ovary is called the capsule. If the capsule is intact, the tumour was contained within the ovary. If the capsule is ruptured, tumour cells may spill into the abdominal cavity, increasing the risk of spread. Rupture can happen before surgery or during surgery, and sometimes it may not be possible for the pathologist to tell when it occurred. A ruptured capsule is associated with a worse prognosis and is used to assign a higher stage.

Has the tumour spread to other organs or tissues in the pelvis or abdomen?

Small tissue samples, called biopsies, are often taken during surgery to check if the tumour has spread outside of the ovary. These biopsies are commonly taken from the lining of the abdomen, called the peritoneum. Another common site is the omentum, a fatty tissue in the abdomen where ovarian cancers often spread.

Sometimes, the tumour grows directly into nearby organs such as the bladder or intestines. If this occurs, the pathologist will examine those tissues carefully under the microscope. The presence of tumour cells in these sites is important for determining both the tumour stage (T stage) and whether there is distant metastatic disease (M stage).

Were lymph nodes examined and did any contain cancer cells?

Lymph nodes are small immune organs located throughout the body. Cancer cells can travel to lymph nodes through lymphatic vessels. For this reason, lymph nodes are often removed and examined.

Your pathology report will include the total number of lymph nodes examined, the number that contained cancer cells, and the size of the largest group of cancer cells. This information is used to determine the nodal stage (pN). Finding cancer cells in lymph nodes increases the risk of the cancer spreading further and helps guide decisions about additional treatment.

• Positive lymph node: A lymph node that contains cancer cells.

• Negative lymph node: A lymph node that does not contain cancer cells.

• Isolated tumour cells (ITCs): Very small groups of cells measuring 0.2 mm or less. These are not counted as positive when determining nodal stage.

• Micrometastasis: A small group of cancer cells between 0.2 mm and 2 mm in size.

• Macrometastasis: A larger group of cancer cells more than 2 mm in size.

• Extranodal extension: Cancer cells breaking through the capsule of the lymph node into surrounding tissue. This is associated with a higher risk of the tumour growing back and may be a reason to consider additional treatment.

How do doctors stage ovarian cancer?

Staging is a way of describing how far a cancer has spread in the body. For ovarian cancer, two main systems are used: the TNM system and the FIGO system. Both are internationally accepted and provide important information about prognosis (the expected outcome) and treatment planning.

The TNM system

The TNM system is developed by the American Joint Committee on Cancer (AJCC). It looks at three main factors:

• T (tumour): Describes the size of the tumour and how far it has spread in or around the ovary or fallopian tube.

• N (lymph nodes): Describes whether cancer cells have spread to nearby lymph nodes.

• M (metastasis): Describes whether cancer has spread to distant parts of the body.

Breakdown of the T stage:

• T1: The tumour is limited to one or both ovaries or fallopian tubes.

  • T1a: Tumour is inside one ovary or fallopian tube, with the outer surface intact and no cancer cells in fluid taken from the abdomen.

  • T1b: Tumour is inside both ovaries or fallopian tubes, but the outer surfaces are intact and no cancer cells are found in fluid.

  • T1c: The tumour is limited to one or both ovaries or tubes, but there has been a rupture, tumour on the outer surface, or cancer cells found in abdominal fluid.

• T2: The tumour has grown into tissues in the pelvis, such as the uterus or bladder.

  • T2a: Spread to the uterus or other fallopian tube or ovary.

  • T2b: Spread to other pelvic tissues.

• T3: The tumour has spread beyond the pelvis into the abdomen or to regional lymph nodes.

  • T3a: Cancer cells are found microscopically outside the pelvis or in nearby lymph nodes.

  • T3b: Visible tumour deposits up to 2 cm outside the pelvis or in nearby lymph nodes.

  • T3c: Visible tumour deposits larger than 2 cm outside the pelvis or involving the capsule of the liver or spleen (without entering the organ itself).

Breakdown of the N stage:

• N0: No cancer cells are seen in regional lymph nodes.

• N0(i+): Only isolated tumour cells smaller than 0.2 mm are seen in the lymph nodes.

• N1: Cancer cells are found in regional lymph nodes.

  • N1a: Deposits up to 10 mm.

  • N1b: Deposits larger than 10 mm.

The FIGO system

The FIGO (International Federation of Gynecology and Obstetrics) system is specifically designed for gynecologic cancers like ovarian cancer. It uses similar criteria to the TNM system but is grouped into broader stages that are easier to interpret clinically.

Breakdown of FIGO stages:

• Stage I: Cancer is limited to the ovaries or fallopian tubes.

  • IA: In one ovary or fallopian tube only.

  • IB: In both ovaries or fallopian tubes.

  • IC: Cancer is still limited to the ovaries or tubes but there has been a rupture, tumour on the surface, or cancer cells found in fluid.

• Stage II: Cancer involves one or both ovaries or tubes with spread to pelvic organs such as the uterus, bladder, or rectum.

  • IIA: Spread to the uterus or other ovary/tube.

  • IIB: Spread to other pelvic tissues.

• Stage III: Cancer has spread outside the pelvis into the abdominal cavity or to regional lymph nodes.

  • IIIA1: Cancer in lymph nodes only.

  • IIIA2: Microscopic spread outside the pelvis.

  • IIIB: Visible spread outside the pelvis up to 2 cm.

  • IIIC: Visible spread larger than 2 cm or spread to the capsule of the liver or spleen.

• Stage IV: Cancer has spread to distant organs outside the abdomen.

  • IVA: Cancer cells are found in the fluid around the lungs.

  • IVB: Cancer has spread to organs such as the liver, spleen, or lymph nodes outside the abdomen.

Why staging matters

Both TNM and FIGO staging systems provide doctors with essential information about how far the cancer has spread. This helps guide treatment choices, such as whether surgery alone is enough or if chemotherapy or other treatments are needed.

Staging also helps predict prognosis. Early-stage disease (stage I) has a much better survival rate compared to advanced-stage disease (stage III or IV). By using staging information, doctors can personalize care and discuss treatment options and expectations with patients.

What is the prognosis for mucinous carcinoma of the ovary?

The outlook is excellent when the tumour is found early. About 90 percent of patients with stage I disease are alive five years after diagnosis. The prognosis decreases with more advanced disease, with about 76 percent survival for stage II and only about 17 percent for stage III or IV.

Tumours with expansile invasion usually have a better outcome than those with infiltrative invasion. Recurrences, when they occur, usually happen within the first three years after diagnosis. Unfortunately, mucinous carcinoma does not respond well to standard chemotherapy, so complete surgical removal is the most important treatment.

Questions to ask your doctor

If you have been diagnosed with mucinous carcinoma of the ovary, you may want to ask your doctor:

• What stage is my tumour and what does that mean for my prognosis?

• Did my tumour show expansile or infiltrative invasion?

• Was the tumour confined to one ovary or has it spread?

• Were any lymph nodes removed and did they contain cancer cells?

• Has immunohistochemistry been performed to confirm that the tumour started in the ovary?

• Are there genetic changes, such as HER2 amplification, that might affect my treatment?

• What treatment options are recommended for me?