A sarcoma is a rare and complex cancer that begins in the bone, cartilage or connective tissue such as muscle, fat, nerves, tendons, lining of joints, lymph vessels or blood vessels.

Sarcoma occurs when abnormal cells in these types of tissue grow in an uncontrolled way. It can develop in any part of the body.

There are two main types of sarcomas, depending on which type of tissue the sarcoma starts in:

1. Soft Tissue Sarcoma
2. Bone Sarcoma

Soft tissue sarcomas can develop anywhere in the body but is more common in the thigh, shoulder and pelvis. There are more than 70 different types of soft tissue sarcomas.

The stages of soft tissue sarcomas are classified by the TNM system, which stands for:

• Tumour (T) – describes the size of the tumour and the extent the cancer has spread. The tumour can be graded from T1 (describing a tumour 5cm or less) to T2 (greater than 5cm).  The letter ‘a’ is used to describe a tumour that is near the surface of the body while ‘b’ indicates that it is deeper in the body.
• Nodes (N) – describes whether the tumour has spread to nearby lymph nodes. Nodes can be graded from N0, where there has been no spread, through to N1, where the cancer has spread the lymph nodes.
• Metastasis (M) – describes whether the cancer has spread to other areas of the body. Metastasis can be graded from M0, where there has been no spread through to M1, where the cancer has spread to other organs of the body and produced additional tumours.

Soft tissue sarcomas are also given a grade (G) from G1 to G3. Soft tissue sarcomas with a higher grade are more aggressive and have a higher likelihood of growing and spreading faster that those with a lower grade.

The TNM ratings are used in combination with the grade to determine the stage of the soft tissue sarcoma.

The following stages are used to describe soft tissue sarcoma of the retroperitoneum (the space in the abdomen behind the abdominal lining) in adults.