Clear Cell Sarcoma, from the CureRays guide library.

Clear cell sarcoma is a rare soft-tissue cancer of younger adults that usually arises near tendons of the foot or ankle; though it makes the same pigment as melanoma, it is a sarcoma defined by its own gene fusion, and it is treated with surgery and radiation, with attention to the lymph nodes.

What it is.

Clear cell sarcoma is a rare soft-tissue sarcoma that most often affects adolescents and younger adults. A sarcoma is a cancer of the body's connective tissues; clear cell sarcoma typically arises deep in the soft tissues near tendons and the tough sheets of tissue called aponeuroses, most commonly in the foot, ankle, or lower leg, and less often in the hands, arms, or trunk. It usually appears as a slowly growing, firm, often painful mass attached to a tendon, and because it grows gradually it may be present for months to years before diagnosis. One of the most distinctive things about clear cell sarcoma is that its cells make melanin, the same pigment found in skin cancer (melanoma), and under the microscope it can closely resemble melanoma — which is why it was once called 'melanoma of soft parts.' Despite that resemblance, it is a true sarcoma, not a skin melanoma, and it is defined at the molecular level by a characteristic gene fusion (an EWSR1 rearrangement) that melanoma does not have; finding that fusion confirms the diagnosis and distinguishes the two. This distinction matters because the two cancers behave and are treated differently. Like a few other sarcomas — and like melanoma — clear cell sarcoma can spread to nearby lymph nodes as well as to the lungs, so the regional nodes are evaluated. The cornerstone of treatment is complete surgical removal with wide margins. Radiation is commonly combined with surgery to treat the microscopic disease that extends beyond the visible tumor and to lower the chance of local recurrence, particularly in the small, functionally important structures of the foot and ankle. Because clear cell sarcoma generally does not respond well to standard chemotherapy, controlling it locally with surgery and radiation, and watching closely for spread, is especially important; clinical trials of targeted and immune therapies are an active area for advanced disease.

How radiation treats it.

Radiation therapy treats clear cell sarcoma by delivering focused beams of energy that damage the DNA inside tumor cells so they can no longer grow and divide. Radiation is an important partner to surgery here for two reasons. First, like other soft-tissue sarcomas, clear cell sarcoma extends microscopically beyond its visible mass — and it characteristically attaches to and creeps along tendons and the tough tissue planes of the foot, ankle, and limb. Removing only the visible tumor risks leaving those microscopic extensions behind to seed a recurrence, so radiation treats a wider zone, following the tissue planes, to sterilize that disease. Second, clear cell sarcoma so often occurs in the small, functionally critical, weight-bearing structures of the foot and ankle in a young person, where removing a very wide margin of tissue would be disabling; pairing a more conservative operation with radiation makes it possible to control the cancer while preserving the limb and its function. Radiation can be given before or after surgery: beforehand it uses a smaller field and a lower dose and can make a function-preserving operation more achievable, though it requires extra attention to wound healing; afterward it treats the tumor bed at a higher dose over a larger area. Modern techniques such as intensity-modulated radiation shape the dose tightly around the target to spare the surrounding tendons, bone, and delicate structures. Clear cell sarcoma is also one of the few sarcomas that — like the melanoma it resembles — can spread to nearby lymph nodes, so radiation may be directed at the regional nodes when they are involved or at risk. Because this tumor responds poorly to standard chemotherapy, strong local control with surgery and radiation, plus close surveillance of the lymph nodes and lungs, carries even more weight than it does for many other sarcomas; for advanced disease, radiation controls symptoms and limited deposits while clinical trials explore targeted and immune therapies.

The ways we can treat it.

Preoperative (neoadjuvant) radiation. Radiation given before surgery treats microscopic disease along tendons and tissue planes using a smaller field and lower dose, which can make a function-preserving operation in the foot or ankle more achievable, at the cost of more wound-healing care.

Postoperative (adjuvant) radiation. Radiation to the tumor bed after surgery, used when preoperative radiation wasn't given, sterilizes microscopic disease left behind and lowers the chance of local recurrence, at a higher dose over a larger area.

Intensity-modulated radiation (IMRT). Shaping the beams tightly around the target spares the surrounding tendons, bone, and small structures of the foot and ankle, helping preserve function in these delicate, weight-bearing locations.

Radiation to lymph nodes. When nearby lymph nodes are involved or at risk — a possibility this tumor shares with melanoma — radiation can treat the nodal area along with, or instead of, surgery to the nodes.

Questions we hear often.

Is clear cell sarcoma the same as melanoma? No, though they look remarkably alike. Clear cell sarcoma makes melanin — the same pigment as melanoma — and under the microscope the two can be nearly indistinguishable, which is why clear cell sarcoma was once called 'melanoma of soft parts.' But it is a true soft-tissue sarcoma, not a skin cancer, and it carries a characteristic EWSR1 gene fusion that melanoma does not have. Finding that fusion is how the diagnosis is confirmed. The distinction matters because the two cancers are treated differently — getting it right ensures you receive the correct surgery, radiation, and, for advanced disease, the appropriate drug therapy or clinical trial.

Why does the team check my lymph nodes? Most soft-tissue sarcomas rarely spread to lymph nodes, but clear cell sarcoma is one of the exceptions — like the melanoma it resembles, it can travel to the nodes near the tumor. Because of this, the team examines and images the regional lymph nodes as part of staging, and if any are involved they are treated with surgery and/or radiation along with the primary tumor. Watching the nodes is an important part of comprehensive care for this particular sarcoma.

Why is local treatment so emphasized for this cancer? Clear cell sarcoma generally does not respond well to standard chemotherapy, so the most effective tools for controlling it are surgery and radiation directed at the tumor and, when needed, the lymph nodes. That makes a complete, well-planned local treatment — wide surgery combined with radiation to cover the microscopic disease along tendons and tissue planes — especially important, along with close follow-up to catch any spread early. For advanced disease, clinical trials of targeted and immune therapies are an active area, and a sarcoma center can help you access them.

This guide is informational only. It is not medical advice — please confirm anything here with your care team.