Epithelioid Sarcoma: Understanding Your Pathology Report

by Jason Wasserman MD PhD FRCPC and Bibianna Purgina MD FRCPC
April 12, 2026

Epithelioid sarcoma is a rare and aggressive type of sarcoma — a cancer that arises from soft tissue. It is called epithelioid because its tumor cells are round and pink-staining, resembling the epithelial cells that normally line the surfaces of organs, even though the tumor does not actually arise from those cells. Epithelioid sarcoma most commonly develops in the hand, wrist, or forearm of young adults, though it can arise elsewhere in the body. It is one of the soft tissue sarcomas most likely to spread to regional lymph nodes, which makes its recognition and thorough staging particularly important. Two subtypes are recognized — the classic (distal) type and the proximal (large cell) type — and these differ in location, microscopic appearance, and behavior.

This article will help you understand the findings in your pathology report — what each term means and why it matters for your care.

What causes epithelioid sarcoma?

Epithelioid sarcoma is caused by inactivation of the SMARCB1 (also known as INI1) gene. SMARCB1 is a tumor suppressor gene — a gene whose normal job is to slow down or stop cell growth. It is part of a large protein complex called SWI/SNF that helps regulate how genes are switched on and off inside cells. When both copies of SMARCB1 are inactivated, this regulatory control is lost, and cells begin to grow uncontrolled. The inactivation of SMARCB1 is not typically inherited — it occurs spontaneously in the tumor cells rather than being passed down through families. No clear environmental or lifestyle risk factors have been identified for epithelioid sarcoma.

What are the symptoms?

The symptoms of epithelioid sarcoma depend on the tumor’s subtype and location. Classic (distal) epithelioid sarcoma most often presents as a slow-growing, painless firm lump in the hand, wrist, finger, or forearm. Because it is slow-growing and often superficial, it can initially be mistaken for a benign cyst, wart, or area of scarring, which sometimes leads to a delay in diagnosis. Over time, the overlying skin may break down, forming an open sore called an ulcer. Proximal (large cell) epithelioid sarcoma tends to arise deeper in the body — in the pelvis, perineum, groin, or axilla — and typically presents as a larger mass. Tumors in these deep locations may not cause any symptoms until they are quite large or until metastasis to nearby lymph nodes is already present.

How is the diagnosis made?

The diagnosis of epithelioid sarcoma is made by examining a tissue sample under the microscope. The sample is obtained through a biopsy — typically a core needle biopsy for deep tumors or an incisional biopsy for superficial lesions. The tissue is sent to a pathologist, who examines it carefully under the microscope.

Epithelioid sarcoma has two subtypes with distinct microscopic appearances. The classic (distal) subtype is made up of round (epithelioid) and elongated (spindle) tumor cells arranged in rounded clusters called nodules. The center of each nodule often shows necrosis — a zone of dead cells — which gives the nodule a target-like appearance under the microscope. This pattern can closely resemble a type of chronic inflammation called a necrotizing granuloma, which is one reason the diagnosis can be missed on initial biopsy. The tumor cells have abundant pink (eosinophilic) cytoplasm, which contributes to their epithelial-like appearance. The proximal (large cell) subtype also comprises epithelioid and spindle cells, but the cells are larger and more overtly malignant-looking, arranged in broad sheets rather than in nodules. Necrosis is common. This subtype more closely resembles other high-grade sarcomas and is less likely to be confused with a granuloma.

Because epithelioid sarcoma can closely mimic carcinoma (cancer arising from true epithelial cells) and other tumors, pathologists use immunohistochemistry (IHC) — a test that detects specific proteins in the tumor cells using chemical stains — to confirm the diagnosis. The tumor cells in epithelioid sarcoma are positive for cytokeratins (proteins normally found in epithelial cells) and for CD34 (a protein normally found on blood vessel and stem cells). This combination of cytokeratin positivity with CD34 positivity is unusual and characteristic. Most importantly, the tumor cells show complete loss of SMARCB1 (INI1) protein staining on IHC — meaning the tumor cells produce no SMARCB1 protein at all, whereas normal surrounding cells stain positively. This loss of SMARCB1 expression confirms the diagnosis and directly reflects the underlying inactivation of the gene that drives tumor growth. Once the diagnosis is confirmed, imaging — typically an MRI of the primary site and a CT of the chest — is performed to assess the full extent of the disease and identify any spread to lymph nodes or distant organs.

Histologic grade

Pathologists do not assign an FNCLCC grade to epithelioid sarcoma. All epithelioid sarcomas — both subtypes — are understood to be high-grade cancers by definition. The FNCLCC grading system is not applied because it does not add meaningful information: the tumor behaves aggressively regardless of the microscopic scoring. Your pathology report will therefore not include a numeric grade, and this is expected and appropriate for this diagnosis. The proximal (large cell) subtype is generally considered to behave more aggressively than the classic (distal) subtype.

Tumor size

The tumor is measured in three dimensions, but only the largest single measurement is typically recorded in your pathology report as the tumor size. Tumor size is one of the factors used to determine the pathologic tumor stage (pT). Tumors 5 cm or smaller are generally associated with a better prognosis than larger tumors. The final tumor size is measured from the surgically removed specimen rather than from a biopsy, which captures only part of the tumor. Classic (distal) epithelioid sarcoma tends to be discovered at a smaller size than the proximal type because of its superficial, visible location.

Tumor extension

Epithelioid sarcoma typically starts in the dermis (the deep layer of the skin) or the soft tissue just beneath the skin, but it can grow into adjacent structures as it enlarges. This spread beyond the original site is called tumor extension. The pathologist carefully examines all tissue submitted with the resection specimen to determine whether tumor cells have grown into surrounding tendons, tendon sheaths, fascia, nerves, blood vessels, or bone. Classic epithelioid sarcoma has a well-recognized tendency to spread along fascial planes and tendon sheaths, sometimes extending well beyond the visible tumor — a key reason it recurs locally even after surgery that appears complete. Extension into surrounding structures increases the pathologic tumor stage (pT) and directly affects surgical planning.

Treatment effect

Some patients with epithelioid sarcoma receive chemotherapy and/or radiation therapy before surgery. This is called neoadjuvant therapy, and its purpose is to shrink the tumor before removal. After surgery, the pathologist examines the removed tissue and estimates the proportion of the tumor that is non-viable (dead) versus viable (still alive). A tumor that is 90% or more non-viable indicates an excellent response to pre-operative therapy and is associated with a better outcome. When a significant proportion of viable tumor remains, additional treatment after surgery may be considered. Your report will describe the estimated percentage of viable and non-viable tumor.

Lymphovascular invasion

Lymphovascular invasion (LVI) means that tumor cells were found inside the thin-walled channels of blood vessels or lymphatic vessels within or near the tumor. Blood vessels carry blood throughout the body; lymphatic vessels carry a fluid called lymph and connect to lymph nodes. When tumor cells enter these channels, they can travel to lymph nodes or distant organs. The presence of LVI is reported as present or absent in your pathology report and is an adverse finding that increases the risk of spread.

Perineural invasion

Perineural invasion means that tumor cells were found attached to or growing along a nerve. Nerves are present throughout the body and carry signals such as pain, pressure, and temperature between the body and the brain. When cancer cells grow along a nerve, they can spread into tissues beyond what is visible at surgery, increasing the risk of local recurrence. Epithelioid sarcoma’s tendency to spread along fascial and tendon structures means perineural invasion — when present — is particularly relevant to surgical planning. Perineural invasion is reported as present or absent.

Surgical margins

In pathology, a margin is the edge of tissue removed during surgery. Margin status indicates whether the entire tumor was removed or whether cancer cells remain at the cut edge of the tissue. Achieving clear (negative) surgical margins is one of the most important goals of epithelioid sarcoma surgery and is the strongest predictor of local control.

• Negative margin — No tumor cells are present at the cut edge. This suggests the tumor was completely removed. The distance from the nearest tumor cells to the margin may also be recorded, as a wider clear margin is associated with a lower risk of local recurrence.
• Close margin — Tumor cells are very close to the cut edge but do not reach it. This may increase the risk of local recurrence and may prompt further treatment such as re-excision or radiation therapy.
• Positive margin — Tumor cells are present at the cut edge, meaning some cancer may remain in the body. Additional surgery or radiation therapy is commonly recommended.

Epithelioid sarcoma has one of the highest local recurrence rates among soft tissue sarcomas, driven in part by its tendency to spread along fascial and tendon planes beyond the visible tumor edge. Achieving wide negative margins — which can be challenging in the hand and fingers — is a key determinant of local control.

Lymph nodes

Epithelioid sarcoma has a notably higher rate of lymph node spread than most other soft tissue sarcomas, particularly the classic (distal) subtype. Approximately 20–40% of patients will develop lymph node metastasis at some point during their disease course. For this reason, careful clinical and imaging assessment of regional lymph nodes is an important part of the workup. Sentinel lymph node biopsy — a procedure in which the first lymph node draining the tumor site is identified and examined — may be performed at specialized centers to detect microscopic spread not visible on imaging.

If any lymph nodes were removed and examined, the pathologist will report the number of nodes examined, the number containing tumor cells, the size of the largest tumor deposit, and whether extranodal extension is present. Extranodal extension means that tumor cells have broken through the outer capsule of the lymph node into the surrounding tissue, which is an adverse finding associated with a higher risk of further spread.

Biomarker and molecular testing

Molecular testing plays a critical role in both confirming the diagnosis of epithelioid sarcoma and guiding treatment decisions, particularly for patients with advanced or recurrent disease.

SMARCB1 (INI1) loss

Loss of SMARCB1 (INI1) protein expression is the defining molecular event in epithelioid sarcoma and is detected by immunohistochemistry as described above. Beyond its diagnostic role, SMARCB1 loss has direct therapeutic implications. The SWI/SNF protein complex — of which SMARCB1 is a component — normally counteracts a different regulatory complex called PRC2. When SMARCB1 is lost, PRC2 becomes overactive, driving uncontrolled tumor growth. Tazemetostat (Tazverik) is a drug that directly inhibits EZH2, the key enzyme within the PRC2 complex. By blocking EZH2, tazemetostat restores some of the regulatory balance that was lost when SMARCB1 was inactivated. Tazemetostat is approved by the FDA for the treatment of adults with locally advanced or metastatic epithelioid sarcoma who are not eligible for complete resection, making it the first targeted therapy approved specifically for this tumor. Response rates in the pivotal clinical trial were approximately 15%, with disease stabilization in a larger proportion of patients. Your oncologist will discuss whether tazemetostat is appropriate in your situation.

Next-generation sequencing (NGS)

In patients with advanced, recurrent, or metastatic epithelioid sarcoma, comprehensive molecular profiling using next-generation sequencing (NGS) may be performed to identify additional genetic changes that could make a patient eligible for a clinical trial or targeted therapy. Research into additional vulnerabilities in epithelioid sarcoma is ongoing, and enrollment in clinical trials is strongly encouraged for patients with advanced disease. Your oncologist will advise whether molecular profiling is appropriate in your situation.

For more information about biomarkers and molecular testing in cancer, visit the Biomarkers and Molecular Testing section of this website.

Pathologic stage (pTNM)

The pathologic stage for epithelioid sarcoma is based on the TNM staging system developed by the American Joint Committee on Cancer (AJCC), 8th edition. This system uses information about the primary tumor (T), lymph nodes (N), and distant metastatic disease (M) to describe the extent of cancer. The M stage — whether the cancer has spread to distant organs such as the lungs — is determined by imaging rather than by the pathology report. In general, a higher stage reflects more advanced disease and a less favorable prognosis. Because epithelioid sarcoma can arise in different body sites, the tumor (pT) staging criteria vary based on where the tumor started.

Tumor stage (pT)

Head and neck:

• pT1 — Tumor is 2 cm or smaller.
• pT2 — Tumor is more than 2 cm but 4 cm or smaller.
• pT3 — Tumor is more than 4 cm.
• pT4 — Tumor has grown into surrounding structures such as the bones of the face or skull, the eye, major blood vessels of the neck, or the brain.

Trunk and extremities (chest wall, back, abdomen, arms, and legs):

• pT1 — Tumor is 5 cm or smaller.
• pT2 — Tumor is more than 5 cm but 10 cm or smaller.
• pT3 — Tumor is more than 10 cm but 15 cm or smaller.
• pT4 — Tumor is more than 15 cm.

Thoracic visceral organs (organs inside the chest):

• pT1 — Tumor is confined to one organ.
• pT2 — Tumor has grown into the connective tissue immediately surrounding the organ where it started.
• pT3 — Tumor has grown into at least one adjacent organ.
• pT4 — Multiple separate tumors are present.

Retroperitoneum (the space at the back of the abdominal cavity):

• pT1 — Tumor is 5 cm or smaller.
• pT2 — Tumor is more than 5 cm but 10 cm or smaller.
• pT3 — Tumor is more than 10 cm but 15 cm or smaller.
• pT4 — Tumor is more than 15 cm.

Orbit (the bony socket surrounding the eye):

• pT1 — Tumor is 2 cm or smaller.
• pT2 — Tumor is more than 2 cm but has not grown into the bones surrounding the eye.
• pT3 — Tumor has grown into the bones surrounding the eye or other bones of the skull.
• pT4 — Tumor has grown into the eye itself or surrounding structures including the eyelids, sinuses, or brain.

• pT0 — No viable tumor found in the resection specimen. This may occur after a complete response to neoadjuvant therapy.
• pTX — The tumor cannot be reliably assessed, for example because the specimen was received as multiple small fragments.

Nodal stage (pN)

• pN0 — No cancer found in any lymph nodes examined.
• pN1 — Cancer found in one or more regional lymph nodes.
• pNX — Lymph nodes were not assessed.

What is the prognosis?

Epithelioid sarcoma is an aggressive sarcoma with a significant risk of local recurrence, lymph node spread, and distant metastasis. Prognosis varies substantially based on subtype, stage, location, and margin status.

Overall five-year survival rates across all stages and sites range from approximately 50–70%, but outcomes differ meaningfully between subtypes and stages:

• Classic (distal) subtype — Generally has a more favorable prognosis than the proximal type. When completely resected with negative margins at an early stage, five-year survival rates approach 70–80%. However, local recurrence is common even after apparently complete surgery, and the disease can follow a prolonged course with multiple recurrences over many years before eventual distant spread.
• Proximal (large cell) subtype — Behaves more aggressively. It tends to present at a larger size and more advanced stage, and distant metastasis is more frequent. Five-year survival rates for the proximal type are generally lower, in the range of 30–50%, though this varies substantially by stage.
• Metastatic disease — Patients with distant metastases at presentation have significantly worse outcomes. The lungs and lymph nodes are the most common metastatic sites. Median survival with metastatic epithelioid sarcoma is typically less than 24 months with current standard treatments, though targeted therapy with tazemetostat and clinical trial access are changing this landscape.

The following features are associated with a worse outcome:

• Proximal (large cell) subtype — Associated with more aggressive behavior and higher risk of distant spread than the classic type.
• Positive surgical margins — The most important predictor of local recurrence. Achieving wide clear margins is the primary surgical goal.
• Lymph node metastasis — Nodal spread significantly worsens prognosis and is more common in epithelioid sarcoma than in most other soft tissue sarcomas.
• Deep tumor location — Tumors arising in deep soft tissue rather than superficially beneath the skin tend to be larger at diagnosis and harder to resect completely.
• Large tumor size — Tumors greater than 5 cm are associated with higher rates of recurrence and distant spread.
• Vascular or perineural invasion — Adverse prognostic findings that increase the risk of systemic spread or local recurrence along tissue planes.

What happens after the diagnosis?

After the diagnosis is confirmed, care is best managed by a multidisciplinary team including a surgical oncologist, a medical oncologist with expertise in sarcoma, and a radiation oncologist. Referral to a specialized sarcoma center is strongly recommended, particularly for proximal-type tumors, large or deeply located tumors, and any patient being considered for targeted therapy or clinical trial enrollment.

Surgery is the primary treatment for localized epithelioid sarcoma. The goal is complete removal with wide negative margins. For tumors of the hand and fingers, achieving wide margins can be technically demanding, and amputation may occasionally be required to achieve the necessary clearance, though limb-sparing surgery is strongly preferred and is usually achievable. The tendency of epithelioid sarcoma to spread along tendon sheaths and fascial planes means the surgical resection must account for this pattern — often requiring removal of more tissue than the visible tumor boundaries suggest.

Regional lymph node assessment is an important component of management that distinguishes epithelioid sarcoma from most other sarcomas. Because nodal spread is relatively common, sentinel lymph node biopsy or formal lymph node dissection may be recommended, particularly for high-risk tumors. Your surgical team will discuss whether nodal staging is appropriate in your case.

Radiation therapy is commonly used after surgery — particularly when margins are close or positive, when the tumor is large, or when complete resection is not achievable. Preoperative radiation may be used in selected cases to facilitate a more complete resection.

Chemotherapy is used for locally advanced, unresectable, or metastatic epithelioid sarcoma. Standard sarcoma chemotherapy regimens — most commonly doxorubicin with or without ifosfamide — are used in this setting, though response rates are modest. Gemcitabine-based regimens are an option in later lines.

Targeted therapy with tazemetostat is available for adults with locally advanced or metastatic epithelioid sarcoma who are not eligible for complete surgical resection. Because essentially all epithelioid sarcomas have lost SMARCB1 expression, all patients with advanced disease are potentially eligible. Tazemetostat is taken orally. Your oncologist will discuss whether this is appropriate in your situation based on your stage and treatment history.

Clinical trial enrollment is strongly encouraged for patients with recurrent, metastatic, or high-risk epithelioid sarcoma. Research into immunotherapy combinations, additional EZH2 pathway inhibitors, and other strategies is active. Your oncologist at a sarcoma center can advise on currently available trials.

Surveillance after treatment includes regular physical examinations, MRI of the primary site, and chest CT to monitor for local recurrence and lung metastases. Given the elevated risk of lymph node spread, regional nodal surveillance is also warranted. Because local recurrence can occur many years after initial treatment, follow-up continues for at least 10 years. The frequency and duration of surveillance will be tailored by your treatment team.

Questions to ask your doctor

• Which subtype of epithelioid sarcoma do I have — classic (distal) or proximal (large cell) — and how does that affect my treatment and prognosis?
• Was the SMARCB1 (INI1) protein loss confirmed by immunohistochemistry?
• Were the surgical margins clear, and how close was the tumor to the edge of the removed tissue?
• Was there any spread along tendon sheaths or fascial planes beyond the main tumor, and does this affect the surgical plan?
• Was lymphovascular or perineural invasion identified in my tumor?
• Should my lymph nodes be assessed, and would a sentinel lymph node biopsy or lymph node dissection be recommended?
• What is the pathologic stage of my tumor?
• Will I need radiation therapy, chemotherapy, or targeted therapy based on these results?
• Am I eligible for treatment with tazemetostat (Tazverik)?
• Are there clinical trials I should consider?
• What imaging will be used to monitor for local recurrence and distant spread, and how often will I be followed?
• Should I be seen at a sarcoma specialty center, and would a second pathology opinion be beneficial?