Your pathology report for uterine carcinosarcoma

by Emily Goebel, MD FRCPC
September 5, 2025

Carcinosarcoma of the uterus is a rare and aggressive type of uterine cancer that contains two components:

  • A carcinoma component, which arises from epithelial cells that line the surface of the uterus.

  • A sarcoma component, which arises from connective tissue.

Because it contains both carcinoma and sarcoma, carcinosarcoma is referred to as a biphasic tumour. It develops from the endometrium, which is the inner lining of the uterus.

Carcinosarcoma is considered a high grade cancer, meaning it tends to grow quickly and spread to other parts of the body. In the past, this tumour was called malignant mixed Müllerian tumour (MMMT), but the preferred term now is carcinosarcoma.

What are the symptoms of carcinosarcoma?

The symptoms of carcinosarcoma are similar to those of other uterine cancers.

They may include:

  • Abnormal uterine bleeding, especially after menopause.

  • Pelvic pain or discomfort.

  • A feeling of pressure or fullness in the abdomen.

  • Unusual vaginal discharge.

  • Unexplained weight loss.

Because these symptoms can be caused by many conditions, it is important to seek medical attention if they occur.

Who gets carcinosarcoma?

Carcinosarcoma accounts for about 5% of all uterine cancers. It usually occurs in postmenopausal women. Like endometrial carcinoma, it shares many of the same risk factors, including obesity, hormone imbalances, and older age.

What causes carcinosarcoma?

The exact cause is not fully understood, but several factors increase the risk:

  • Age: Most cases occur in postmenopausal women.

  • Previous radiation therapy: Pelvic radiation for another cancer may increase the risk. Carcinosarcoma can appear 5 to 20 years after radiation treatment.

  • Tamoxifen therapy: About 6% of women with carcinosarcoma have a history of tamoxifen use, a drug used for breast cancer.

  • Obesity and hormone imbalance: Prolonged exposure to estrogen without progesterone can stimulate abnormal endometrial growth.

How does carcinosarcoma develop?

Research shows that both the carcinoma and sarcoma components of carcinosarcoma often share the same genetic changes. This means the sarcoma develops from the carcinoma through a process called epithelial–mesenchymal transition (transdifferentiation).

Most carcinosarcomas have mutations in the TP53 gene, which are also common in a type of endometrial cancer called serous carcinoma. Other mutations are less common.

How is the diagnosis made?

The diagnosis is usually made after tissue is removed from the uterus, either by biopsy, curettage, or hysterectomy. The tissue is then examined under the microscope by a pathologist.

What does carcinosarcoma look like under the microscope?

When examined under the microscope, carcinosarcoma shows two distinct cancerous parts:

The sarcoma part may contain:

  • Homologous elements, meaning tissue normally found in the uterus, such as smooth muscle.

  • Heterologous elements, meaning tissue not normally found in the uterus, such as skeletal muscle (rhabdomyosarcoma), cartilage (chondrosarcoma), or bone (osteosarcoma).

The presence of heterologous elements may be associated with a worse prognosis.

What special tests are performed to confirm the diagnosis?

Pathologists often use immunohistochemistry, a test that uses stains to highlight proteins in the cells to help confirm the diagnosis of carcinosarcoma.

  • The carcinoma component is usually positive for cytokeratins.

  • The sarcoma component may be positive for proteins such as desmin or actin, and if it resembles rhabdomyosarcoma, it will be positive for myogenin or MyoD1.

  • Many carcinosarcomas are strongly positive for p53, reflecting TP53 mutations.

These tests help confirm the diagnosis and distinguish carcinosarcoma from other tumours.

Myometrial invasion

The myometrium is the thick muscular wall of the uterus. Carcinosarcoma often invades from the endometrium into the myometrium. The depth of invasion is described in millimeters and as a percentage of the total myometrial thickness. Deeper invasion is associated with a higher risk of spread and is used to help determine the tumor stage.

Cervical stromal invasion

If the tumour spreads into the cervical stroma (the supportive tissue of the cervix), it is considered more advanced and requires a higher stage. This finding may influence treatment decisions, such as the need for more extensive surgery or radiation.

Invasion of surrounding organs or tissues

Carcinosarcoma can grow beyond the uterus into nearby organs such as the ovaries, fallopian tubes, vagina, bladder, or rectum. The term adnexa refers to the ovaries, fallopian tubes, and ligaments connected to the uterus. When these structures are removed during surgery, the pathologist carefully examines them for tumour spread. If cancer is present, the stage increases and the prognosis is worse.

Lymphovascular invasion

Lymphovascular invasion (LVI) means that cancer cells have entered small blood vessels or lymphatic channels within or around the tumour. This is an important finding because once cancer cells are inside these channels, they can travel to nearby lymph nodes or to distant organs such as the lungs or liver. For carcinosarcoma, LVI is seen in about one-third of cases and is considered a marker of aggressive disease. Because of this, LVI often influences treatment decisions, and patients with this finding are more likely to be offered additional therapy such as radiation or chemotherapy after surgery.

Margins

A margin is the edge of tissue removed during surgery. Pathologists carefully examine the margins under the microscope to see if cancer cells are present at the very edge of the tissue. Margins are only reported when the uterus (or other tissue) has been surgically removed.

  • A negative margin means that no cancer cells are seen at the cut edge of the tissue. This suggests that the tumour was completely removed. Negative margins are an important goal of surgery because they reduce the risk of the cancer coming back in the same area.

  • A positive margin means that cancer cells extend to the cut edge of the tissue. This raises concern that some tumour cells may have been left behind in the body. Positive margins are associated with a higher chance of local recurrence, and additional treatment such as radiation or chemotherapy may be recommended.

Margins described in carcinosarcoma reports include:

  • Cervical margin: where the uterus meets the cervix.

  • Vaginal cuff margin: if part of the vagina was removed.

  • Parametrial margin: tissue and ligaments around the uterus.

  • Peritoneal margin: the lining of the abdominal cavity.

Margin

Lymph nodes

Lymph nodes are small immune organs that filter lymph fluid and trap harmful substances such as bacteria and cancer cells. Carcinosarcoma spreads to lymph nodes more frequently than many other types of endometrial cancer, which is why lymph nodes from the pelvis and abdomen are often removed and examined under the microscope.

Your pathology report will usually include:

  • The total number of lymph nodes removed.

  • The number of lymph nodes that contain cancer cells.

For example, your report may say “3 of 15 lymph nodes positive for metastatic carcinoma,” which means that cancer cells were found in 3 out of 15 lymph nodes examined. The more lymph nodes that contain cancer, the higher the risk of recurrence and the more advanced the stage.

When cancer is found in a lymph node, the size of the deposit may also be described as follows:

  • Isolated tumour cells (ITCs): Clusters of cells 0.2 mm or smaller.

  • Micrometastasis: Deposits between 0.2 mm and 2 mm.

  • Macrometastasis: Deposits larger than 2 mm.

Finding cancer in lymph nodes means the disease has spread beyond the uterus, which increases the stage and usually requires additional treatment such as chemotherapy or radiation.

Lymph node

Pathologic stage (pTNM)

Carcinosarcoma of the uterus is staged using the TNM system, which is based on three components:

  • T (tumour): How far the tumour has grown into the uterus and surrounding tissues.

  • N (nodes): Whether cancer has spread to nearby lymph nodes.

  • M (metastasis): Whether cancer has spread to distant organs such as the lungs or liver.

Each part of the TNM system is given a number or letter, and together these determine the overall stage. In general, higher numbers mean more advanced disease and a worse prognosis.

Tumour stage (pT)

  • T1: Tumour is confined to the uterus.

  • T2: Tumour has grown into the cervix.

  • T3: Tumour has grown through the wall of the uterus and onto its outer surface, or into the fallopian tubes or ovaries.

  • T4: Tumour has grown into nearby organs such as the bladder or rectum.

Nodal stage (pN)

  • N0: No cancer cells are found in lymph nodes.

  • N1mi: Tumour cells are present in at least one pelvic lymph node, but the area is very small (isolated tumour cells or micrometastasis).

  • N1a: Tumour cells are found in at least one pelvic lymph node, and the area is larger than 2 millimeters (macrometastasis).

  • N2mi: Tumour cells are present in at least one para-aortic lymph node, but the area is very small (isolated tumour cells or micrometastasis).

  • N2a: Tumour cells are found in at least one para-aortic lymph node, and the area is larger than 2 millimeters (macrometastasis).

  • NX: No lymph nodes were sent for examination.

FIGO staging

In addition to TNM, carcinosarcoma of the uterus is staged using the FIGO system, which was developed by the International Federation of Gynecology and Obstetrics and is widely used by gynecologists. FIGO staging is based on how far the tumour has spread within the uterus, into lymph nodes, or to distant organs.

  • Stage I: Tumour is confined to the uterus.

    • IA: Less than half of the myometrium (the muscular wall of the uterus) is invaded.

    • IB: More than half of the myometrium is invaded.

  • Stage II: Tumour has spread into the cervical stroma but remains confined to the uterus.

  • Stage III: Tumour has spread beyond the uterus but not outside the pelvis.

    • IIIA: Tumour has spread to the outer surface of the uterus, fallopian tubes, or ovaries.

    • IIIB: Tumour has spread to the vagina or parametrial tissues.

    • IIIC1: Tumour has spread to pelvic lymph nodes.

    • IIIC2: Tumour has spread to para-aortic lymph nodes.

  • Stage IV: Tumour has spread to nearby or distant organs.

    • IVA: Tumour has invaded the bladder or rectum.

    • IVB: Tumour has spread to distant organs such as the lungs, liver, or bones.

Staging is important because it guides treatment decisions and helps predict prognosis.

Prognosis for carcinosarcoma

Carcinosarcoma is one of the most aggressive forms of uterine cancer. Prognosis depends mainly on stage, but other features also play a role.

  • Patients with stage I–II disease have about a 60% chance of surviving 5 years after diagnosis.

  • Patients with stage III disease have about a 25% chance of 5-year survival.

  • Patients with stage IV disease have a 10% chance of 5-year survival.

Other factors linked to a poorer prognosis include:

  • Tumour size greater than 5 cm.

  • More than 50% myometrial invasion.

  • Lymphovascular invasion.

  • Sarcoma predominance.

  • Serous carcinoma in the epithelial component.

  • Heterologous sarcoma components such as rhabdomyosarcoma or chondrosarcoma.

Because carcinosarcoma is aggressive, treatment often includes a combination of surgery, chemotherapy, and radiation therapy.

Questions to ask your doctor

  • What stage is my carcinosarcoma?

  • How many lymph nodes were removed and how many contained cancer?

  • Were my margins positive or negative?

  • Did my tumour show heterologous elements such as cartilage or muscle?

  • What treatments do you recommend after surgery?

  • What is my risk of recurrence, and how will follow-up be managed?

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