Dedifferentiated chondrosarcoma

by Bibianna Purgina MD FRCPC
November 10, 2023

Dedifferentiated chondrosarcoma is an aggressive type of cancer made up of tumour cells that resemble cartilage. The tumour is called ‘dedifferentiated’ because it develops from within a more well-differentiated type of cartilage cancer called conventional chondrosarcoma.

What are the symptoms of dedifferentiated chondrosarcoma?

Symptoms of dedifferentiated 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 body area.

What causes dedifferentiated chondrosarcoma?

At present doctors do not know what causes dedifferentiated chondrosarcoma.

Can dedifferentiated chondrosarcoma spread to other parts of the body?

Yes. The tumour cells in dedifferentiated chondrosarcoma can metastasize (spread) from the tumour to other parts of the body. The most common site of distant metastasis is the lung.

How is the diagnosis of dedifferentiated chondrosarcoma made?

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. In some cases, a biopsy may show features highly suspicious for dedifferentiated chondrosarcoma, but the diagnosis can only be made after the entire tumour is removed and available for examination under the microscope.

What does dedifferentiated chondrosarcoma look like under the microscope?

When examined under the microscope, dedifferentiated chondrosarcoma is made up of two parts. The first part consists of cartilage-producing tumour cells. This part resembles the better differentiated conventional chondrosarcoma. The second part is made up of non-cartilage-producing tumour cells. This part can look like other types of sarcomas including osteosarcoma, undifferentiated pleomorphic sarcoma, angiosarcoma, leiomyosarcoma, and rhabdomyosarcoma. It is the combination of better differentiated conventional chondrosarcoma with another type of high-grade sarcoma that allows pathologists to make the diagnosis of dedifferentiated chondrosarcoma.

About this article

This article was written by doctors to help you read and understand your pathology report for dedifferentiated chondrosarcoma. The sections below describe the results found in most pathology reports, however, all reports are different and results may vary. Importantly, some of this information will only be described in your report after the entire tumour has been surgically removed and examined by a pathologist. Contact us if you have any questions about this article or your pathology report. Read this article for a more general introduction to the parts of a typical pathology report.

​What grade is dedifferentiated chondrosarcoma?

All dedifferentiated chondrosarcomas are classified as grade 3 (high-grade) tumours.

Has the tumour spread into surrounding organs or tissues?

Tumours that start in a bone can break through the outer surface of 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 and why are margins important?

In pathology, a margin is the edge of a tissue that is cut when removing a tumour from the body. The margins described in a pathology report are very important because they tell you if the entire tumour was removed or if some of the tumour was left behind. The margin status will determine what (if any) additional treatment you may require.

Most pathology reports only describe margins after a surgical procedure called an excision or resection has been performed to remove the entire tumour. For this reason, margins are not usually described after a procedure called a biopsy is performed to remove only part of the tumour. The number of margins described in a pathology report depends on the types of tissues removed and the location of the tumour. The size of the margin (the amount of normal tissue between the tumour and the cut edge) also depends on the type of tumour being removed and the location of the tumour.

Pathologists carefully examine the margins to look for tumour cells at the cut edge of the tissue. If tumour cells are seen at the cut edge of the tissue, the margin will be described as positive. If no tumour cells are seen at the cut edge of the tissue, a margin will be described as negative. Even if all of the margins are negative, some pathology reports will also provide a measurement of the closest tumour cells to the cut edge of the tissue.

A positive (or very close) margin is important because it means that tumour cells may have been left behind in your body when the tumour was surgically removed. For this reason, patients who have a positive margin may be offered another surgery to remove the rest of the tumour or radiation therapy to the area of the body with the positive margin. The decision to offer additional treatment and the type of treatment options offered will depend on a variety of factors including the type of tumour removed and the area of the body involved. For example, additional treatment may not be necessary for a benign (non-cancerous) type of tumour but may be strongly advised for a malignant (cancerous) type of tumour.

What information is used to determine the pathologic stage for dedifferentiated chondrosarcoma?

​The pathologic stage for dedifferentiated chondrosarcoma 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 tissue submitted and give each part a number. In general, a higher number means a 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 dedifferentiated chondrosarcoma

For bone cancers such as dedifferentiated chondrosarcoma, the primary tumour (pT) stage depends on where the tumour is 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 and whether there is a separate tumour nodule(s).

• pT1: Tumor ≤ 8 cm in greatest dimension.
• pT2: Tumor > 8 cm in greatest dimension.
• pT3: Discontinuous tumours 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 tumour 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 tumour 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 tumour thrombus in major pelvic vessels.

If your pathologist cannot reliably evaluate the tumour 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 dedifferentiated chondrosarcoma

Cancers including dedifferentiated 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 dedifferentiated chondrosarcoma

Cancers including dedifferentiated 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.

Other helpful resources

Atlas of pathology