Jason Wasserman MD PhD FRCPC
March 4, 2026
Carcinosarcoma of the uterus is an aggressive type of cancer that starts in the uterus. It is sometimes described as a “biphasic” tumour because it contains two different kinds of cancer cells.
One part is made up of cells that resemble those that normally line the inside surface of organs. This is called the carcinoma component. The other part is composed of cells that resemble the body’s supporting tissues, such as muscle or connective tissue. This is called the sarcoma component.
In the past, carcinosarcoma was often called malignant mixed Müllerian tumour. This is an older term, and the preferred name is now carcinosarcoma.
Even though it contains a sarcoma-like component, carcinosarcoma usually starts as a carcinoma. Over time, some of the tumour cells change and begin to look like sarcoma. For this reason, carcinosarcoma is treated more like a high-grade endometrial carcinoma than a primary uterine sarcoma.
What are the symptoms of carcinosarcoma of the uterus?
The most common symptom of carcinosarcoma of the uterus is abnormal vaginal bleeding, especially bleeding after menopause. Some people also notice watery or blood-tinged vaginal discharge.
Other symptoms may include uterine enlargement, pelvic pressure, pelvic pain, or a pelvic mass. These symptoms may occur when the tumour becomes large and fills the uterine cavity.
Because bleeding after menopause is not normal, it should always be evaluated.
What causes carcinosarcoma of the uterus?
Carcinosarcoma shares many of the same risk factors as other types of endometrial carcinoma and most often occurs in postmenopausal women.
Some cases occur in people with a history of tamoxifen use, usually taken in the past for breast cancer. Carcinosarcoma can also occur as a late complication of pelvic radiation therapy, typically many years after treatment.
The exact cause is not fully understood, but genetic changes within tumour cells play an important role. Many tumours exhibit TP53 gene alterations, similar to those seen in endometrial serous carcinoma.
How is this diagnosis made?
The diagnosis of uterine carcinosarcoma usually begins with an endometrial biopsy, in which a small sample of tissue is removed from the lining of the uterus and examined under the microscope by a pathologist.
If cancer is identified, surgery is often performed to remove the uterus and often the ovaries, fallopian tubes, and lymph nodes. The removed tissue is carefully examined to determine tumor spread, depth of invasion, lymph node involvement, and other important features. This is important because carcinosarcoma often behaves aggressively, and a significant number of patients have spread beyond the uterus at the time of diagnosis.
Microscopic features
When examined under a microscope, carcinosarcoma shows a mixture of carcinoma and sarcoma. These two components are often sharply separated, though they can also be mixed.
The carcinomatous component is high grade and most commonly shows endometrioid or serous differentiation, although clear cell and undifferentiated carcinoma can also be present. The sarcomatous component is usually a high-grade sarcoma that does not resemble a specific normal tissue type.
In some cases, the sarcomatous component contains heterologous elements, meaning the tumour shows tissue types not normally found in the uterus. Examples include rhabdomyosarcoma (skeletal muscle-like tissue), chondrosarcoma (cartilage-like tissue), and rarely osteosarcoma (bone-like tissue).
Many tumours show areas of necrosis (tumour cell death) and haemorrhage (bleeding). Deep myometrial invasion and lymphatic and vascular invasion are relatively common.
When carcinosarcoma spreads to other parts of the body, metastases often contain the carcinomatous component.
Immunohistochemistry
Immunohistochemistry is a laboratory test that uses antibodies to detect specific proteins inside tumor cells. In most cases, the diagnosis of carcinosarcoma is made based solely on microscopic appearance.
Immunohistochemistry may be used in some cases to help confirm a specific type of sarcomatous differentiation. For example, if the tumour contains rhabdomyoblastic differentiation, markers of skeletal muscle differentiation may be performed to support this interpretation. Immunohistochemistry can also help in difficult cases when the tumour is fragmented or when one component is present only in a small amount.
FIGO grade
The FIGO grade system for endometrial endometrioid carcinoma is largely based on the extent of solid growth. Carcinosarcoma of the uterus is considered high grade by definition, so it is not typically assigned FIGO grades 1, 2, or 3.
For this tumour type, the most important prognostic and treatment information is usually the stage and the presence of specific high-risk features described elsewhere in the pathology report.
Biomarkers
Biomarkers are tests performed on tumour tissue to understand better how a cancer behaves and which treatments may be most effective. These tests may include immunohistochemistry (to detect specific proteins in tumour cells) and molecular testing (to detect changes in DNA). Not all biomarkers are tested in every case.
Mismatch repair proteins (MMR)
Mismatch repair proteins help normal cells fix small mistakes that occur during DNA replication. The four most commonly tested proteins are MLH1, PMS2, MSH2, and MSH6, which work together in pairs.
Pathologists usually test MMR proteins using immunohistochemistry. Results are reported as either retained expression (normal) or loss of expression (abnormal).
Mismatch repair protein loss is uncommon in carcinosarcoma. If one or more mismatch repair proteins are lost, the tumour is described as mismatch repair–deficient. This may raise the possibility of Lynch syndrome, and additional testing may be recommended in the appropriate clinical setting. Mismatch repair–deficient tumours may also be eligible for immunotherapy in advanced or recurrent disease.
p53
p53 is a tumour suppressor protein that helps control cell growth and repair damaged DNA.
An abnormal p53 result indicates that the TP53 gene is altered. This is usually reported as aberrant, mutant-type, or abnormal p53 expression. Abnormal p53 expression is very common in carcinosarcoma and reflects the high frequency of TP53 mutation in this tumour type.
POLE
POLE mutations occur in a small subset of endometrial cancers. Tumours with POLE mutations typically have many DNA mutations but can behave less aggressively.
POLE mutations are rare in carcinosarcoma. When present, they may be associated with a more favourable prognosis. Results are reported as mutated or wild-type (normal).
Additional molecular findings
Carcinosarcoma often shows genetic changes similar to high-grade endometrial carcinomas. Alterations in genes involved in cell growth pathways can be present. In many cases, molecular profiling places the tumour into a high-risk molecular category, discussed further in the TCGA section below.
TCGA molecular subtypes
Many endometrial cancers can be grouped into four molecular subtypes, based on large genomic studies such as those from The Cancer Genome Atlas (TCGA). The biomarkers described above help place a tumour into one of these categories, which can provide important prognostic information.
Most carcinosarcomas fall into the p53-abnormal (copy-number high) molecular subtype. This group is associated with TP53 mutation, genomic instability, and aggressive clinical behaviour.
A smaller proportion falls into the no specific molecular profile (NSMP) group. Tumours with mismatch repair deficiency or POLE mutations are uncommon in carcinosarcoma.
Understanding which molecular subtype a tumour belongs to helps doctors estimate prognosis and may influence treatment planning.
Other features to look for in your pathology report
Myometrial invasion
Myometrial invasion describes how deeply the tumor has grown into the muscle wall of the uterus.
The uterus is made up of an inner lining (the endometrium) and a thick outer muscle layer called the myometrium. When the tumor spreads from the lining into this muscle, it is called myometrial invasion.
Pathologists measure the depth of invasion in millimetres and often report it as a percentage of the total thickness of the myometrium. Invasion of less than 50% of the myometrial thickness is associated with a lower risk. Invasion of 50% or more is associated with a higher risk of spread to lymph nodes.
This measurement is critical because it directly affects the tumor stage. In carcinosarcoma, deep invasion is also associated with a higher risk of recurrence.
Cervical stromal invasion
Cervical stromal invasion means the tumor has grown from the body of the uterus into the supportive tissue of the cervix.
The cervix is the lower part of the uterus that connects to the vagina. If the tumor involves only the surface lining of the cervix, this does not change the stage. However, if it invades the deeper cervical stroma, the stage increases.
This finding may influence the need for additional treatment such as radiation therapy.
Invasion of surrounding organs or tissues
The uterus is closely connected to several other organs and tissues, such as the ovaries, fallopian tubes, vagina, bladder, and rectum. The term “adnexa” refers to the fallopian tubes, ovaries, and ligaments directly linked to the uterus.
As a tumour grows, it can spread into any of these organs or tissues. In such cases, some parts of these organs or tissues may have to be removed along with the uterus. A pathologist will thoroughly examine these organs or tissues for tumour cells, and the findings will be detailed in your pathology report.
The presence of tumour cells in other organs or tissues raises the pathologic tumour stage and is linked with a poorer prognosis. In carcinosarcoma, spread beyond the uterus is relatively common at diagnosis.
Lymphatic and vascular invasion
Lymphatic and vascular invasion means tumor cells are seen inside small lymphatic channels or blood vessels.
Lymphatic vessels are part of the immune system and allow fluid to drain from tissues. Blood vessels carry blood throughout the body. When tumor cells enter these channels, they have a pathway to spread to lymph nodes or distant organs.
Pathologists look for tumour cells inside these channels under the microscope. This finding does not mean the tumour has already spread, but it does increase the risk of spread. Because of this, lymphatic and vascular invasion is considered a high-risk feature and may lead your doctor to recommend additional treatment after surgery.
Margins
A margin refers to the edge of the tissue removed during surgery, such as a hysterectomy. After the surgery, pathologists examine the tissue margins under a microscope to check for any remaining cancer cells. In the case of carcinosarcoma of the uterus, several specific margins are carefully evaluated:
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Cervical margin: This is the edge where the uterus meets the cervix. Pathologists examine this margin to see if the cancer has spread into or beyond the cervix.
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Vaginal cuff margin: If the top portion of the vagina is removed along with the uterus, the pathologist will check the vaginal cuff margin to ensure no cancer cells are present at the surgical edge.
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Parametrial margin: This margin includes the tissue around the uterus, including ligaments and connective tissue. It is examined to see if cancer has spread into these areas.
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Peritoneal margin: If the peritoneum (the lining of the abdominal cavity) is removed, it will be examined to check for cancer cells in this area.
If any of these margins contain cancer cells, it is referred to as a positive margin, which may mean that some tumour cells were left behind after surgery. A negative margin means no cancer cells were found at the edges, suggesting that the tumour was completely removed. Clear margins are important for reducing the risk of the cancer returning, and positive margins may lead to recommendations for additional treatments, such as radiation therapy.
Lymph nodes
Lymph nodes are small, bean-shaped structures in the lymphatic system that help fight infection and remove waste from the body. Lymph nodes contain immune cells that filter lymph fluid as it travels through lymphatic vessels and help trap harmful substances such as bacteria or cancer cells.
In uterine carcinosarcoma, lymph nodes are examined because this tumour has a higher risk of metastasis. During surgery, lymph nodes from the pelvis and sometimes the abdomen may be removed and sent to a pathologist. Each lymph node is examined under the microscope to look for metastatic cancer, meaning cancer cells that have spread from the uterus.
Examining lymph nodes is important for determining the stage of the cancer, guiding treatment decisions, and estimating prognosis. If cancer cells are found in the lymph nodes, your doctor may recommend additional treatment such as chemotherapy and/or radiation therapy.
Isolated tumour cells (ITCs)
Pathologists use the term “isolated tumour cells” to describe a group of tumour cells measuring 0.2 mm or less and found in a lymph node. If only isolated tumour cells are found in all the lymph nodes examined, the pathologic nodal stage is pN1mi.
Micrometastasis
Micrometastasis is a group of tumour cells measuring 0.2-2 mm found in a lymph node. If only micrometastases are found in all the lymph nodes examined, the pathologic nodal stage is pN1mi.
Macrometastasis
Macrometastasis is a group of tumour cells measuring more than 2 mm in a lymph node. Macrometastases are associated with a worse prognosis and often lead to recommendations for additional treatment.
Pathologic stage (pTNM)
The pathologic stage for carcinosarcoma of the uterus is based on the TNM staging system, an internationally recognized system 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 submitted tissue and assign each part a number.
In general, a higher number means a more advanced disease and a worse prognosis.
Tumour stage (pT) for carcinosarcoma of the uterus
Carcinosarcoma of the uterus is given a tumour stage between T1 and T4 based on the depth of myometrial invasion and growth of the tumour outside of the uterus.
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T1 – The tumour only involves the uterus.
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T2 – The tumour has grown to involve the cervical stroma.
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T3 – The tumour has grown through the wall of the uterus and is now on the outer surface of the uterus, OR it has grown to involve the fallopian tubes or ovaries.
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T4 – The tumour has grown directly into the bladder or the colon.
Nodal stage (pN) for carcinosarcoma of the uterus
Based on examination of lymph nodes from the pelvis and abdomen, carcinosarcoma of the uterus is staged from N0 to N2.
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N0 – No tumour cells were found in any lymph nodes examined.
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N1mi – Tumour cells were found in at least one lymph node from the pelvis, but the area with cancer cells was not larger than 2 millimetres (only isolated cancer cells or micrometastasis).
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N1a – Tumour cells were found in at least one lymph node from the pelvis, and the area with cancer cells was greater than 2 millimetres (macrometastasis).
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N2mi – Tumour cells were found in at least one lymph node outside the pelvis, but the area with cancer cells was not larger than 2 millimetres (only isolated cancer cells or micrometastasis).
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N2a – Tumour cells were found in at least one lymph node outside the pelvis, and the area with cancer cells was greater than 2 millimetres (macrometastasis).
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NX – No lymph nodes were sent for examination.
FIGO stage
The FIGO staging system, developed by the International Federation of Gynecology and Obstetrics, is a standardized method for classifying endometrial cancers based on their extent of spread. This system is important because it helps doctors determine the extent of the cancer, plan appropriate treatment, and estimate the prognosis.
Stage I: The cancer is confined to the uterus.
IA: The cancer is limited to the endometrium or has invaded less than halfway into the myometrium.
Prognosis: Stage I–II carcinosarcoma has a better prognosis than more advanced stages, but carcinosarcoma is generally treated aggressively because it has a higher risk of recurrence than low-grade endometrioid carcinoma.
IB: The cancer has invaded more than halfway into the myometrium.
Prognosis: Deep myometrial invasion is associated with a higher risk of spread and recurrence and often leads to recommendations for additional therapy.
Stage II: The cancer has spread from the uterus to the cervix but has not gone beyond the uterus.
Prognosis: Stage II cancers are more likely to require additional treatments such as chemotherapy and radiation therapy.
Stage III: The cancer has spread beyond the uterus but is still within the pelvis.
IIIA: The cancer has spread to the outer surface of the uterus or to nearby tissues.
IIIB: The cancer has spread to the vagina or the pelvic wall.
IIIC: The cancer has spread to the lymph nodes.
Prognosis: Stage III cancers are more advanced and often require a combination of surgery, radiation, and chemotherapy. The prognosis is more guarded, but treatment can still be effective in some cases.
Stage IV: The cancer has spread to distant organs, such as the bladder, bowel, or lungs.
IVA: The cancer has spread to nearby organs such as the bladder or rectum.
IVB: The cancer has spread to distant organs, such as the lungs or liver.
Prognosis: Stage IV cancers are the most advanced and carry a more serious prognosis. Treatment at this stage is usually focused on managing symptoms and slowing disease progression.
Questions to ask your doctor
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What is my stage?
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Was the tumour confined to the uterus or had it spread beyond the uterus?
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How deeply did the tumor invade the myometrium?
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Were lymph nodes involved?
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Was lymphatic and vascular invasion present?
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Were biomarker tests performed, and do any results affect treatment options?
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What does my stage and TCGA molecular subtype mean for my prognosis?
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