Chondrosarcoma

by Bibianna Purgina, MD FRCPC
September 3, 2022


What is chondrosarcoma?

Chondrosarcoma is a type of cancer made up of cartilage. Chondrosarcomas can start within a bone or any other part of the body where cartilage is normally found. The most common locations for chondrosarcoma are the spine and pelvis. It typically affects older adults and is the second most common type of bone sarcoma.

What are the symptoms of chondrosarcoma?

Symptoms of chondrosarcoma include pain and swelling over the involved bone. Larger tumours can cause the bone to fracture (break) which can cause a sudden increase in pain and inability to use the affected area of the body.

How do pathologists make the diagnosis of chondrosarcoma?

This diagnosis is usually made after a small sample of tissue is removed in a procedure called a biopsy. The biopsy is sent to a pathologist who examines the tissue under a microscope. Another surgery is then performed to remove the entire tumour which will also be sent to a pathologist for examination. Some patients will be offered radiation and/or chemotherapy before surgery.

Chondrosarcoma

What are the types of chondrosarcoma?

Pathologists divide chondrosarcoma into histologic types based on the way the cells look when examined under the microscope and where on the bone the tumour is growing. The histologic types of chondrosarcoma are conventional, clear cell, mesenchymal, and undifferentiated. The histologic type is used to determine the tumour grade.

Conventional chondrosarcoma

Conventional chondrosarcoma is the most common type of chondrosarcoma. These tumours start on the inside of a bone in a space called the medulla. Conventional chondrosarcomas are locally aggressive tumours which means they can grow into surrounding organs and tissues. Tumour cells from conventional chondrosarcoma, however, rarely spread to other parts of the body.

Clear cell chondrosarcoma

Clear cell chondrosarcoma is a very small growing tumour that is normally found in the femur or humerus. The tumour is made up of large cells that appear clear when examined under a microscope. Clear cell chondrosarcoma can grow into surrounding organs and tissues, especially if not removed completely. Tumour cells can also spread to other parts of the body such as the lungs.

Mesenchymal chondrosarcoma

Mesenchymal chondrosarcoma is an aggressive type of chondrosarcoma that commonly grows outside of the bone and into surrounding organs and tissues. The tumour is made up of small cells with a high nuclear to cytoplasmic ratio (the nucleus is large while the cytoplasm is small). Mesenchymal chondrosarcomas harbor a HEY1-NCOA2 fusion gene that can be identified by molecular tests such as fluorescence in situ hybridization (FISH) or next-generation sequencing (NGS).

Dedifferentiated chondrosarcoma

Dedifferentiated chondrosarcoma is an aggressive type of chondrosarcoma that grows out of a pre-existing conventional type of chondrosarcoma. Pathologists use the term transformation to describe this change.

How do pathologists grade chondrosarcoma?

Grade is a way of comparing the cells in a tumour to normal bone cells. In general, tumours that look more like normal cells are given a lower grade while those that look less like normal cells are given a higher grade.

For conventional chondrosarcoma, the grade ranges from 1 (low) to 3 (high) and pathologists look for 3 microscopic features when determining the grade: cellularity (the number of cells in the tumour), cytologic atypia (how abnormal the tumour cells look compared to normal bone cells), and mitotic activity (the number of tumour cells dividing to create new tumour cells). Grade 1 tumours are called hypocellular because they contain a small number of tumour cells and the cells look very similar to normal bone cells. Grade 2 tumours contain more tumour cells, the cells are typically hyperchromatic (darker), and the tissue surrounding the tumour cells may be described as myxoid. Grade 3 tumours are called hypercellular because they contain lots of tumour cells and the tumour cells are often described as atypical because they look very little like normal bone cells. Mitotic figures (tumour cells dividing to create new tumour cells) are usually also seen.

Unlike conventional chondrosarcoma, clear cell chondrosarcoma, mesenchymal chondrosarcoma, and dedifferentiated chondrosarcoma are always given the same grade. Specifically, clear cell chondrosarcoma is always grade 1 (low grade) while mesenchymal and dedifferentiated chondrosarcoma are always grade 3 (high grade).

Why is the grade important for chondrosarcoma?

Grade is important for chondrosarcoma because it is used to predict how the tumour will behave over time. For example, a grade 1 tumour can regrow in the same location after surgery but it is rare for the tumour cells to spread to more distant parts of the body. Higher grade tumours (grade 2 and 3) are more likely to spread to distant parts of the body and are usually associated with a worse prognosis.

Has the tumour spread into surrounding organs or tissues?

Larger chondrosarcomas can break through the bone and grow into the surrounding organs or tissue such as muscle, tendons, or the joint space. If this has occurred, it may be included in your report and is usually described as extraosseous extension. If the tumour has grown into another part of the bone, that will also be described in your report. Tumour extension is important because it is used to determine the pathologic tumour stage (pT).

What is a margin?

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 regrow in the same site after treatment (local recurrence).

Margin

What is the pathologic stage for chondrosarcoma?

​The pathologic stage for chondrosarcoma 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.

The pathologic stage will only be included in your report after the entire tumour has been removed. It will not be included after a biopsy.

Tumour stage (pT) for chondrosarcoma

For bone cancers such as chondrosarcoma, the primary tumour (pT) stage depends on where the tumour was located in your body.

Tumours in the appendicular skeleton

​These are bones of your appendages and include the arms, legs, shoulder, trunk, skull, and facial bones. A tumour from these regions is given a tumour stage from 1-3 based on tumour size whether there is a separate tumor nodule(s).

  • pT1: Tumor ≤ 8 cm in greatest dimension.
  • pT2: Tumor > 8 cm in greatest dimension.
  • pT3: Discontinuous tumors in the primary bone site.
Tumours in the spine

Tumours located in the spine are given a tumour stage from 1-4 based on the extent of tumor growth.

  • pT1: Tumor confined to one vertebral segment or two adjacent vertebral segments.
  • pT2: Tumor confined to three adjacent vertebral segments.
  • pT3: Tumor confined to four or more adjacent vertebral segments, or any nonadjacent vertebral segments.
  • pT4: Extension into the spinal canal or great vessels.
Tumours in the pelvis

Tumours located in your pelvis are given a tumour stage from 1-4 based on the size of the tumour and the extent of tumor growth.

  • pT1: Tumor confined to one pelvic segment with no extraosseous (growing outside of the bone) extension.
    • pT1a: Tumor ≤ 8 cm in greatest dimension.
    • pT1b: Tumor >8 cm in greatest dimension.
  • pT2: Tumor confined to one pelvic segment with extraosseous extension or two segments without extraosseous extension.
    • pT2a: Tumor ≤ 8 cm in greatest dimension.
    • pT2b: Tumor >8 cm in greatest dimension.
  • pT3: Tumor spanning two pelvic segments with extraosseous extension.
    • pT3a: Tumor ≤ 8 cm in greatest dimension.
    • pT3b: Tumor >8 cm in greatest dimension.
  • pT4: Tumor spanning three pelvic segments or crossing the sacroiliac joint.
    • pT4a: Tumor involves sacroiliac joint and extends medially to the sacral neuroforamen (space where the nerves pass through).
    • pT4b: Tumor encasement of external iliac vessels or presence of gross tumor thrombus in major pelvic vessels.

If your pathologist cannot reliably 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) for chondrosarcoma

Primary bone cancers including chondrosarcoma are given a nodal stage of 0 or 1 based on finding cancer cells in one or more lymph nodes.

  • Nx – No lymph nodes were sent to pathology for examination.
  • N0 – No cancer cells are found in any of the lymph nodes examined.
  • N1 – Cancer cells were found in at least one lymph node.
Metastasis stage (pM) for chondrosarcoma

Primary bone cancers including chondrosarcoma are given a metastatic stage only if the presence of metastasis has been confirmed by a pathologist.  There are two metastatic stages in primary bone sarcomas, M1a and M1b.  If there are confirmed lung metastasis, then the tumor metastatic stage is 1a.

The metastatic stage can only be given if tissue from a distant site is sent for pathological examination. Because this tissue is rarely present, the metastatic stage cannot be determined, and it is typically not included in your report.

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