This article will help you read and understand your pathology report for chordoma.
by Bibianna Purgina, MD FRCPC, reviewed on December 21, 2018
Bones are a special type of tissue that provide our body with support and protection. In total there are 206 bones in our body. Some bones (like the bones in our fingers) are very small while other bones (like the bone in our upper leg) are very big.
Chordoma is a cancer that almost always develops in bone. Chordoma is a type of cancer called a sarcoma. Sarcomas are cancers that develop from mesenchymal tissues such as fat, bone and muscle.
Chordomas develop from cells left over from an embryonic structure called the notochord. The notochord helps to form the spine during fetal development. Once the spine has formed, the cells of the notochord usually disappear. Sometimes small areas of notochord cells remain and it is from these left over cells (called remnants) that chordoma develops.
The two most common locations are the sacrum (the bottom of the spine in the pelvis) and the base of the skull. Very rarely chordoma can develop in non-bone locations away from the midline of the body.
Most chordomas occur in older patients, usually between the ages of 40 to 70 although they can occur in younger patients including children. Chordomas are very slow growing tumours and can reach a very large size, especially those that develop around the pelvis.
Symptoms related to chordoma depend on the location of the tumour. Chordomas that develop in the skull base can cause headaches or vision problems. Those that develop in the pelvis can cause bladder or bowel problems or tingling in the legs.
Chordoma can be difficult to treat because of their location near important structures such as the spinal cord and brain. Sometimes chordoma can spread to other parts of the body (metastasize). The most common location that chordoma spreads to is the lungs.
The first diagnosis of a chordoma is usually made after a small piece of the tumour (a biopsy) is removed and sent to a pathologist for examination. Under the microscope, chordomas are made of round to oval shaped tumour cells. Some of the tumour cells will have small holes inside of the cells which pathologists describe as vacuoles. The tumour cells with vacuoles are called physaliferous cells.
After a pathologist makes a diagnosis of chordoma, most patients undergo surgery to remove the tumour although some patients may be offered radiation therapy before surgery. Chordoma is a type of cancer that usually does not respond to chemotherapy.
After the tumour is removed, your pathologist will examine it under the microscope and provides your surgeon and oncologist with critical information required for your subsequent treatment.
There are different types of chordoma and each one is called a histologic type. Your pathologist will determine the histologic type of your tumour after examining it under the microscope. The histologic type is based on the way the tumour looks under the microscope.
The histologic types of chordoma include:
Some chordomas will change over time so that some of the cells no longer resemble normal chordoma cells. This process is called dedifferentiation and these chordomas are then called dedifferentiated chordoma.
Your pathologist can only determine the type of chordoma you have after tissue from the tumour is examined under the microscope.
Why is this important? The histologic type of chordoma is important because it is used to determine the grade (see Histologic grade below).
Grade is a word pathologists use to describe how different the cancer looks compared to the normal cells in the bone. Bone tumours are graded on a scale of 1 to 3 with grade 1 tumours considered ‘low grade’ while grade 3 tumours are considered ‘high grade’.
For most bone tumors, the grade is determined by the histologic type of the tumor (see Histologic type above).
Conventional, cellular and chondroid chordomas are grade 2 (intermediate grade), but poorly differentiated and dedifferentiated chordomas are grade 3 (high grade).
Why is this important? Grade is important because it is used to predict the behavior of the tumour. For example, grade 1 tumours may come back in the same location (local recurrence) but it is rare for them to spread to more distant parts of the body (metastasize). Higher grade tumours (grade 2 and 3) are more likely to spread to distant parts of the body and are usually associated with worse prognosis.
These tumours are measured in three dimensions but only the largest dimension is typically included in the report. For example, if the tumour measures 5.0 cm by 3.2 cm by 1.1 cm, the report may describe the tumour size as 5.0 cm in greatest dimension.
Tumour size will only be described in your report after the entire tumour has been removed.
Large chordomas often break through the bone and grow into the surrounding tissue including adjacent organs, muscle, tendons, or the joint space. If this has occurred, it may be included in your report and is usually described as extraosseous extension.
Some bones are made up of multiple parts. If the chordoma has grown from one part into another, your report will describe the tumour as invading adjacent bones. This is particularly important for tumours in the spine or pelvis as both bones are made up of multiple parts.
If you have been diagnosed with chordoma on a biopsy, you usually will have surgery first to remove your tumour. In some cases of chordoma, pre-surgery radiation therapy may be given. If you have received radiation therapy before your surgery, your pathologist will examine all the tissue sent to pathology to see how much of the tumour is still alive (viable).
The presence of cancer cells wrapped around a nerve is called perineural invasion. Perineural invasion is important because cancer cells can travel along a nerve to tissues far away from the original tumour.
Perineural invasion is not commonly seen in chordoma.
Lymphatics and blood vessels are channels that normal cells use to travel around the body. The presence of cancer cells within a lymphatic or blood vessel is called lymphovascular invasion and is associated with a higher risk that the cancer cells will travel (metastasize) to a distant site such as the lungs. Chordomas rarely metastasize to lymph nodes.
A margin is any tissue that was cut by the surgeon to remove the bone (or part of the bone) and tumour from your body. Depending on the type of surgery you have had, the types of margins, which could include proximal (the part of the bone closest to the middle of your body) and distal (the part of the bone farthest from the middle of your body) bone margins, soft tissue margins, blood vessel margins, and nerve margins.
All margins will be very closely examined under the microscope by your pathologist to determine the margin status. A margin is considered negative when there are no cancer cells at the edge of the cut tissue. A margin is considered positive when there are cancer cells at the 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 (local recurrence).
Chordomas that occur in the skull base are often taken out as multiple small pieces which make it impossible for the pathologist to examine the margins of the tissue. In this situation, completeness of the surgery will be determined by the radiologist using post-operative imaging such as CT scan or MRI scans.
Margins will only be described in your report after the entire tumour has been removed and the tumour has not been removed in multiple pieces.
Metastatic disease describes the process where cancer cells escape the main tumour and travel to another part of the body. Lymph nodes are small immune organs located throughout the body. Many cancers can spread to the lymph nodes, but chordoma does this very rarely. If lymph nodes were part of the surgery to remove your tumour, your pathologist will assess them under the microscope and describe whether or not there are any cancer cells in the lymph node.
If lymph nodes were removed as part of your surgery, then your report will include the total number of lymph nodes examined and the number that contain cancer cells.
The pathologic stage for chordoma 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.
Tumour stage (pT)
For bone cancers or sarcomas such as chordoma, the primary tumour (pT) stage depends on where the tumour was located in your body.
If your chordoma was located in your appendicular skeleton (specially the bones of the skull), it is given a tumour stage from 1-3 based on tumour size whether there a separate tumor nodule(s).
If your chordoma was located in your spine, it is given a tumour stage from 1-4 based on the extent of tumor growth.
If your chordoma was located in your pelvis, it is given a tumour stage from 1-4 based on the size of the tumour and extent of tumor growth.
If after microscopic examination, no tumour is seen in the resection specimen sent to pathology for examination, it is given the tumour stage pT0 which means there is no evidence of primary tumour.
If your pathologist cannot reliable evaluate the tumor size or the extent of growth, it is given the tumour stage pTX (primary tumour cannot be assessed). This may happen if the tumour is received as multiple small fragments.
Nodal stage (pN)
Primary bone cancers are given a nodal stage between 0 and 1 based on the presence or absence of cancer cells in one or more lymph nodes.
If no cancer cells are seen in any lymph nodes, the nodal stage is 0. If no lymph nodes are sent for pathological examination, the nodal stage cannot be determined, and the nodal stage is listed as NX. If cancer cells are found in any lymph nodes, then the nodal stage is listed as N1.
Metastasis stage (pM)
Bone sarcomas are given a metastasis stage only if the presence of metastasis has been confirmed by a pathologist. There are two metastasis stages in primary bone sarcomas, M1a and M1b. If there are confirmed lung metastasis, then the tumor metastasis stage is 1a.
The metastasis stage can only be given if tissue from a distant site is sent for pathological examination. Because this tissue is rarely present, the metastasis stage cannot be determined, and it is typically not included in your report.