Tumours of uncertain tissue type
Many soft tissue sarcomas are made up of different types of cells. This can make it difficult to tell what type of cell they developed from. The following are the most common types of soft tissue sarcomas of uncertain (unknown) origin.
Alveolar soft-part sarcoma
Alveolar soft-part sarcoma is a rare tumour. It usually occurs in young adults and affects women more often than men. This type of tumour most commonly develops in the legs. It grows slowly, but it is known to spread, or metastasize, to the lungs, brain or bones in the early stages.
Clear cell sarcoma
Clear cell sarcoma is a rare, slow-growing tumour. It usually develops in the tendons of the arms or legs in young adults. In many cases, this cancer has already spread to other parts of the body when it is diagnosed.
Clear cell sarcoma is similar to melanoma in some ways. For example, it contains brown pigment (melanin) similar to melanoma. For many years, clear cell sarcomas were thought to be a melanoma rather than a soft tissue sarcoma. But clear cell sarcomas have specific genetic changes that set them apart from melanoma.
Desmoplastic small round cell tumour
Desmoplastic small round cell tumour is a rare soft tissue sarcoma. It most often affects children, adolescents and young adults. It usually occurs in the fibrous tissue in the abdomen. The tumour is made up of small, round cancer cells surrounded by scar-like tissue.
Epithelioid sarcoma most often develops in soft tissues under the skin of the upper extremities, often in a finger, hand or forearm. It usually affects adolescents and young adults. This type of cancer commonly spreads to the lymph nodes and lungs.
Extraskeletal Ewing sarcoma and primitive neuroectodermal tumour
Ewing sarcoma usually develops in bone (see Ewing sarcoma). But about one-third of Ewing sarcomas are found in soft tissues. These include extraskeletal Ewing sarcoma and peripheral primitive neuroectodermal tumour (pPNET).
Extraskeletal Ewing sarcoma starts in the soft tissues around the bones. They can start anywhere in the body, but usually occur in the trunk, extremities (legs and arms), head and neck. Extraskeletal Ewing sarcomas tend to behave differently from other soft tissue sarcomas. The cells of these tumours look and act very much like Ewing sarcoma of the bone, so they are usually treated like bone sarcoma.
pPNET is very rare. It can occur anywhere, but it usually develops in the chest, abdomen, pelvis and extremities (legs and arms). pPNETs share many features with Ewing sarcoma of the bone and extraskeletal Ewing sarcoma and are usually treated like bone sarcoma.
Extraskeletal myxoid chondrosarcoma
Extraskeletal myxoid chondrosarcoma is a rare type of soft tissue sarcoma that affects older adults and usually occurs in the deep soft tissues of the lower extremities.
Malignant mesenchymoma is a rare type of soft tissue sarcoma. These tumours have features of fibrosarcoma and at least 2 other types of soft tissue sarcoma.
Malignant PEComa gets its name from its mixture of perivascular and epithelioid cells. PEComa is usually non-cancerous, or benign. It can also be cancerous, or malignant, which means that it can spread, or metastasize, to other parts of the body.
Spindle cell tumour and spindle cell sarcoma
Spindle cell tumour and spindle cell sarcoma don’t look like any type of specific cancer, which means that doctors can’t give a specific diagnosis. The tumour may be considered a sarcoma or another type of cancer that looks like a sarcoma under the microscope.
Synovial sarcoma is a cancerous, or malignant, tumour that develops in the synovium, which is the synovial tissue lining the joints. This is an uncommon tumour that usually develops in children or young adults, and it develops more often in boys than in girls.
Synovial sarcoma usually develops in the knee or ankle. It can also develop in a hand, shoulder or hip. These tumours can spread, or metastasize, to the skin, particularly the scalp.
Although they are called synovial sarcomas, these tumours don’t start from or even look like synovial tissue. It is not known what type of cells synovial sarcomas start in. For this reason, they are sometimes classified as a sarcoma of uncertain (unknown) origin.