Epithelioid Sarcoma, from the CureRays guide library.

Epithelioid sarcoma is a rare, slow-growing soft-tissue cancer of younger adults that usually starts as a firm nodule on a hand, forearm, or lower leg; it is treated with surgery and radiation, with a newer targeted pill now available for advanced disease.

What it is.

Epithelioid sarcoma is a rare soft-tissue sarcoma that tends to occur in adolescents and younger adults. A sarcoma is a cancer of the body's connective tissues; epithelioid sarcoma is unusual in that its cells look somewhat like the cells that line surfaces (epithelial cells), which can make it tricky to diagnose. The 'classic' (distal) form most often begins on a hand, finger, forearm, or lower leg as one or more firm, slowly growing nodules in or just under the skin; because these can ulcerate or look like a non-healing sore or a wart, the diagnosis is sometimes delayed. A less common 'proximal' form arises in the trunk, pelvis, or groin, tends to be more aggressive, and occurs in somewhat older adults. Epithelioid sarcoma usually grows slowly, but it has two behaviors that shape treatment: it tends to creep along tendons, nerves, and fascial planes, spreading microscopically beyond the visible nodule and often producing new nodules nearby; and, unlike most soft-tissue sarcomas, it can spread to nearby lymph nodes as well as to the lungs. At the molecular level, the great majority of epithelioid sarcomas have lost a protein called INI1 (SMARCB1), and detecting this loss helps confirm the diagnosis and has opened a targeted treatment option. The cornerstone of treatment is complete surgical removal with wide margins, because of the tumor's tendency to track along tissue planes. Radiation is commonly combined with surgery to treat the microscopic disease that extends beyond what can be removed, lowering the chance of local recurrence and helping preserve the hand or limb. Because the tumor can travel to lymph nodes, the team also evaluates and watches the regional nodes. For advanced or inoperable disease, a newer targeted pill (an EZH2 inhibitor) that exploits the INI1 loss is now an option.

How radiation treats it.

Radiation therapy treats epithelioid sarcoma by delivering focused beams of energy that damage the DNA inside tumor cells so they can no longer grow and divide. Radiation is a natural partner to surgery here because of the way this tumor grows: rather than staying within a single, well-defined nodule, epithelioid sarcoma creeps microscopically along tendons, nerves, and fascial planes and tends to produce new nodules nearby. Removing only the visible nodule risks leaving behind those microscopic extensions, which then seed a local recurrence. Radiation treats a wider zone — designed to follow the tissue planes the tumor travels along — sterilizing that microscopic disease so the cancer is less likely to come back and so a hand, finger, or limb can be preserved when wide surgery alone would be disfiguring. This is particularly valuable because the classic form so often occurs in the small, functionally important structures of a hand or forearm in a young person. 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 and the path of microscopic spread at a higher dose over a larger area. Because the target is often elongated to follow tissue planes, techniques such as intensity-modulated radiation shape the dose tightly around that irregular volume while sparing the delicate surrounding structures. Epithelioid sarcoma is also one of the few sarcomas that can spread to nearby lymph nodes, so radiation may be directed at the regional nodes when they are involved or at risk. For advanced disease, radiation is used to control symptoms or treat a limited number of deposits, while the targeted EZH2-inhibitor pill works throughout the body by exploiting the tumor's characteristic INI1 loss. Across these settings, radiation's strength is treating disease that extends beyond the reach of the scalpel — the central challenge of this slow but stubbornly infiltrative cancer.

The ways we can treat it.

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

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

Intensity-modulated radiation (IMRT). Shaping the beams tightly around an often-elongated target spares surrounding tendons, bone, and the small structures of a hand or foot, helping preserve function in these delicate locations.

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

Questions we hear often.

My nodule grew slowly and looked harmless — why is it cancer? Epithelioid sarcoma is known for being slow-growing and for looking deceptively benign — it can resemble a wart, a cyst, a callus, or a non-healing sore, and it sometimes ulcerates. That appearance, combined with its rarity, is why the diagnosis is sometimes delayed. But it is a true cancer that can spread along tissue planes, to nearby lymph nodes, and to the lungs. The key to diagnosis is expert pathology, including a test that detects loss of the INI1 (SMARCB1) protein, which is present in the large majority of these tumors. If you have a firm, persistent, or ulcerating nodule on a hand, forearm, or lower leg that isn't healing, it deserves evaluation and, if needed, a biopsy at a sarcoma center.

Why does the team check my lymph nodes? Most soft-tissue sarcomas rarely spread to lymph nodes, but epithelioid sarcoma is one of the exceptions — 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 addressed with surgery and/or radiation along with treatment of the primary tumor. Watching the nodes is an important part of comprehensive care for this particular sarcoma and is one of the ways it differs from most others.

What is the new targeted pill I've heard about? The great majority of epithelioid sarcomas have lost a protein called INI1 (SMARCB1), and that loss makes the tumor cells dependent on a related protein called EZH2. A pill called tazemetostat blocks EZH2 and is approved for epithelioid sarcoma that can't be surgically removed or has spread. It offers a targeted option beyond chemotherapy for advanced disease. It does not replace surgery and radiation, which remain the main treatments for tumors that can be removed, but it is an important addition for advanced cases — and a good example of how understanding a tumor's specific genetics opens new treatments.

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