by Emily Goebel, MD FRCPC
May 27, 2022
Uterine carcinosarcoma is a type of cancer that develops in the uterus. It is called carcinosarcoma because, unlike most tumours, it is made up of two parts – a carcinoma and a sarcoma – that look different when examined under the microscope. Another name for carcinosarcoma is malignant mixed Mullerian tumour (MMMT).
Carcinosarcoma of the uterus is usually diagnosed after a small sample of tissue is removed from the endometrium in a procedure called a biopsy or curettage. Once the diagnosis is made, the tumour is removed in a resection specimen known as a hysterectomy.
When examined under the microscope, the tumour is made up of two parts – a carcinoma and a sarcoma. Both parts of the tumour are cancerous. The carcinoma part of the tumour is made up of abnormal epithelial cells. These cells are normally found on the inside of the endometrium. For that reason, the carcinoma part can look like other more common types of cancer that start in the endometrium including endometrioid carcinoma, serous carcinoma, or clear cell carcinoma. The sarcoma part is made up of abnormal spindle cells. These cells are normally found in connective tissue.
The sarcoma part can have homologous or heterologous elements. Homologous means that the sarcoma looks like the connective tissue normally found in the uterus, such as stroma or smooth muscle. Heterologous means that the sarcoma looks like connective tissue not normally found inside the uterus, such as skeletal muscle (which pathologists call rhabdomyosarcoma) or cartilage (which pathologists call chondrosarcoma). The presence of heterologous elements is important because it may be associated with a worse prognosis.
Your pathologist may perform a test called immunohistochemistry on your tissue sample to confirm the diagnosis. The carcinoma part is usually positive for proteins called cytokeratins. The sarcoma part may or may not be positive for cytokeratins, and can be positive for proteins called desmin or actin. The entire tumour is usually strongly positive of p53. If there is a part of the tumour that looks like rhabdomyosarcoma (see above), it will be positive for the muscle markers myogenin and MyoD1.
The myometrium is a thick band of muscle just below the endometrium. The movement of tumour cells from the endometrium into the myometrium is called myometrial invasion. The amount of myometrial invasion will be described in millimetres and as a percentage of the total myometrial thickness. Myometrial invasion is an important prognostic feature and is used to determine the tumour stage (see Pathological stage below).
The cervix is a structure at the very bottom of the uterus. The cervix connects directly with the endometrium. The wall of the cervix is made up of a type of tissue called the stroma.
Carcinosarcoma may grow from the endometrium into the cervix. After the tumour is removed completely, your pathologist will carefully examine the tissue from the cervix to see if there are any tumour cells in the cervical stroma. This examination is important because finding tumour cells in the cervical stroma increases the tumour stage (see Pathologic stage below).
Several other organs and tissues are directly attached to or are very close to the uterus including the ovaries, fallopian tubes, vagina, bladder, and rectum. Adnexa or adnexal are terms used to describe the fallopian tubes, ovaries, and ligaments connected directly to the uterus. As the tumour becomes bigger, it can grow directly into any of these organs or tissue. When this happens, parts of these other organs or tissues may need to be removed at the same time as the uterus. Your pathologist will carefully examine these other organs or tissues for tumour cells and the results will be described in your pathology report. Finding tumour cells in other organs or tissues is important because it increases the pathologic tumour stage and is associated with a worse prognosis.
Blood moves around the body through long thin tubes called blood vessels. Another type of fluid called lymph which contains waste and immune cells moves around the body through specialized vessels called lymphatics. The term lymphovascular invasion is used to describe tumour cells that are found inside a blood or lymphatic vessel. Lymphovascular invasion is important because these cells are able to metastasize (spread) to other parts of the body such as lymph nodes or the lungs.
A margin is the normal tissue that surrounds a tumour and is removed with the tumour at the time of surgery. The margins will only be described in cases where the tumour extends into the cervical stroma or other tissues surrounding the uterus and after the entire tumour has been removed.
The type and number of margins described in your report will depend on the type of surgical procedure performed to remove the tumour. A margin is called positive when there are tumour cells at the very edge of the cut tissue. A positive margin is associated with a higher risk that the tumour will recur in the same site after treatment. A negative margin means that no tumour cells were seen at any of the cut edges of tissue.
Lymph nodes are small immune organs located throughout the body. Tumour 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 tumour cells from the tumour to a lymph node is called metastasis.
Your pathologist will carefully examine each lymph node for tumour cells. Lymph nodes that contain tumour cells are often called positive while those that do not contain any tumour cells are called negative. Most reports include the total number of lymph nodes examined and the number, if any, that contain tumour cells.
Lymph nodes on the same side as the tumour are called ipsilateral while those on the opposite side of the tumour are called contralateral. Lymph nodes examined are usually divided into those found in the pelvis and those found around a large blood vessel in the abdomen called the aorta. The lymph nodes found around the aorta are called para-aortic.
If tumour cells are found in a lymph node, the size of the area involved by tumour cells will be measured and described in your report.
All carcinosarcomas of the uterus are considered high grade and are not graded according to the FIGO system.
The pathologic stage for carcinosarcoma 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 a worse prognosis.
Uterine carcinosarcoma 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.
Uterine carcinosarcoma is given a nodal stage from N0 to N2 based on the examination of lymph nodes from the pelvis and abdomen.
Uterine carcinosarcoma is given a metastatic stage of M0 or M1 based on the presence of tumour 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.