Biphenotypic Sinonasal Sarcoma: Understanding Your Pathology Report

Section Editor: Jason Wasserman MD PhD FRCPC
October 26, 2026

Biphenotypic sinonasal sarcoma (BSNS) is a rare, slow-growing cancer that starts inside the nose. It is a type of sarcoma, meaning it develops from the body’s connective tissues rather than the lining of the nose. The tumor usually grows in the upper nasal cavity or the ethmoid sinuses, the small air spaces between the eyes.

Biphenotypic means the tumor cells show features of two different cell types at once. Under the microscope and with special tests, the cells look partly like nerve-supporting cells and partly like muscle cells. Biphenotypic sinonasal sarcoma is found mostly in adults, usually around age 50, and it affects women about twice as often as men.

This article explains how doctors diagnose biphenotypic sinonasal sarcoma and which tests confirm it. It also describes what the grade, margins, and stage in your pathology report mean for your care.

What causes biphenotypic sinonasal sarcoma?

Biphenotypic sinonasal sarcoma is caused by a change in a gene called PAX3 inside the tumor cells. In most tumors, a piece of PAX3 breaks off and joins part of another gene, creating an abnormal fusion gene. The fusion acts like a switch stuck in the “on” position, telling cells to keep growing.

This genetic change develops in the tumor cells during a person’s life. It is not inherited or passed on to children. No lifestyle or environmental cause of biphenotypic sinonasal sarcoma has been identified.

What are the symptoms of biphenotypic sinonasal sarcoma?

The symptoms of biphenotypic sinonasal sarcoma come from a growing mass that blocks the nose. Because the tumor grows slowly, symptoms can be mild for a long time. Common symptoms include:

A blocked or stuffy nose that makes breathing through the nose difficult.
Nosebleeds.
Pressure, pain, or congestion in the face or sinuses.

When the tumor grows into the space around the eye, it can cause bulging of the eye or double vision. These symptoms resemble those of more common conditions, such as nasal polyps and chronic sinus infections.

How is the diagnosis of biphenotypic sinonasal sarcoma made?

The diagnosis of biphenotypic sinonasal sarcoma is made after tissue from the tumor is examined under the microscope by a pathologist. An ear, nose, and throat surgeon usually takes a biopsy during nasal endoscopy, using a thin camera passed through the nostril. Sometimes the diagnosis is made only after the pathologist examines the entire tumor.

Under the microscope, biphenotypic sinonasal sarcoma is made of long, thin spindle cells arranged in sweeping bundles. The tumor cells look fairly uniform, and very few of them are dividing. The tumor often surrounds and traps the normal lining of the nose, called respiratory-type mucosa. It also tends to spread into the surrounding tissue in an infiltrative pattern.

Several other spindle cell tumors of the nose can look similar, so pathologists use additional tests to confirm the diagnosis. Molecular tests can find the PAX3 change in the tumor cells. A common method is fluorescence in situ hybridization (FISH), which uses glowing probes to show whether the PAX3 gene has broken apart. Next-generation sequencing (NGS) can also identify the exact partner gene.

In about 6 in 10 tumors, PAX3 is joined to a gene called MAML3. Less often, the partner is FOXO1 or NCOA1, and in some tumors the partner cannot be identified. A small number of tumors show no detectable change, and the diagnosis then rests on the microscopic appearance and the stains described below.

Once the diagnosis is confirmed, CT and MRI scans show how far the tumor extends into the sinuses, the eye socket, and the base of the skull. Your report may also include a panel of stains used to confirm the diagnosis, which is described in the next section.

Immunohistochemistry

Immunohistochemistry is used in almost every case of biphenotypic sinonasal sarcoma, because it shows the two cell types that give the tumor its name. Immunohistochemistry uses antibodies to show which proteins are present in tumor cells. The results also help separate this tumor from other spindle cell tumors of the nose. Results that may appear in your report include:

S100. Positive, at least in some tumor cells, in nearly all cases. S100 is a protein found in nerve-supporting cells, so a positive result indicates a neural component of the tumor.
Smooth muscle actin (SMA). Positive in the tumor cells in nearly all cases. SMA is a muscle protein; a positive result indicates the muscle side of the tumor.
Desmin, myogenin, and MyoD1. These muscle proteins are positive in some tumors and negative in others. A positive result does not change the diagnosis.
SOX10. Negative in the tumor cells, even though they share some features with nerve-supporting cells. SOX10 is usually positive in nerve sheath tumors, so a negative result helps rule them out.
Cytokeratins. Negative in the tumor cells. A positive result would raise the possibility of a different tumor, such as synovial sarcoma.
Beta-catenin. Often positive in the nucleus of the tumor cells. This result supports the diagnosis but is also seen in some other nasal tumors.

Laboratories use different panels, and not every report will include every stain.

Histologic grade

Biphenotypic sinonasal sarcoma is a low-grade sarcoma by definition. The World Health Organization (WHO) classification of head and neck tumors groups it with the connective tissue tumors of the nose and sinuses. The current version is the 5th edition, published in 2022.

Grade describes how abnormal the tumor cells look and how quickly they are likely to grow. In biphenotypic sinonasal sarcoma, the cells look only mildly abnormal, very few are dividing, and areas of dead tumor are usually absent. Because every tumor of this type is low grade, pathologists do not assign it a separate numbered grade.

Many other soft tissue sarcomas are graded using a scoring system called FNCLCC, but pathologists do not use it for biphenotypic sinonasal sarcoma. Your report may describe the tumor as low grade, or it may not mention grade at all. Both are expected for this diagnosis.

Tumor size

The size of a biphenotypic sinonasal sarcoma is measured in centimeters (cm) and recorded in your pathology report. Many of these tumors measure about 4 cm across when found. Size helps your care team understand how much of the nose and sinuses the tumor involves and plan surgery.

Endoscopic surgery often removes tumors in the nose in several pieces. In that case, the pathologist may not be able to measure the entire tumor. The pathologist may then use the size from your CT or MRI scan instead.

Tumor extension

Biphenotypic sinonasal sarcoma starts in the nasal cavity or sinuses but can grow into nearby structures as it enlarges. This spread beyond the original site is called tumor extension. In about 1 in 4 people, the tumor has grown into the eye socket (orbit) by the time it is diagnosed.

The tumor can also grow through the thin bone at the base of the skull, toward the brain. The pathologist examines the tissue for tumor in bone and other structures, and the surgeon and the scans add information about areas the pathologist cannot see. Extension into these structures is one of the most important findings for planning surgery and radiation.

Lymphovascular invasion

Lymphovascular invasion means tumor cells are seen inside a blood vessel or lymphatic channel. In most cancers, this finding raises concern that tumor cells could travel to other parts of the body. Lymphovascular invasion is not a typical feature of biphenotypic sinonasal sarcoma, and many reports do not mention it. If your report does, it will state whether it identified lymphovascular invasion.

Surgical margins

A margin is the edge of tissue the surgeon cuts to remove the tumor. For biphenotypic sinonasal sarcoma, margins are reported as follows:

Negative margin. No tumor cells are seen at the cut edge. Your report may also give the distance from the tumor to the closest margin, because a wider rim of normal tissue lowers the risk of the tumor growing back.
Positive margin. Tumor cells are seen at the cut edge. This means some tumor may remain, and your care team may consider further surgery or radiation therapy.

Because this tumor spreads into the surrounding tissue, achieving clear margins in the nose can be difficult. When the tumor is removed in several pieces, the pathologist may be unable to assess the margins at all. In that case, the surgeon’s findings and follow-up scans help show whether any tumor remains.

Lymph nodes

Lymph nodes are small immune organs that filter fluid from the tissues. No reports describe spread of biphenotypic sinonasal sarcoma to lymph nodes. For this reason, lymph nodes in the neck are not usually removed during surgery for this tumor.

If lymph nodes are removed for another reason, your report will say how many were examined and whether any contained tumor cells.

Biomarker and molecular testing

For most people with biphenotypic sinonasal sarcoma, there are currently no established biomarker tests that guide the choice of a specific targeted drug. Molecular testing on this tumor, usually FISH or NGS to detect the PAX3 change, is used to confirm the diagnosis. As described above under “How is the diagnosis made?” it does not, by itself, guide treatment.

Research into the PAX3 fusion in this tumor is ongoing. When the tumor returns or cannot be removed, broader molecular profiling may be performed to look for changes that could make a person eligible for a clinical trial. Your care team can discuss whether this testing is appropriate for you. More information about these tests is available in our Biomarkers and Genetic Testing section.

Pathologic stage (pTNM)

No staging system is designed for biphenotypic sinonasal sarcoma. Most cancers are staged using the TNM system in the AJCC Cancer Staging Manual, 8th edition, which the pathologist reports as a pTNM stage. Neither of the two College of American Pathologists (CAP) protocols that might seem relevant applies to this tumor.

CAP nasal cavity and paranasal sinuses protocol. This protocol (version 4.3.0.0, 2026) covers carcinomas of the nose and sinuses. It specifically excludes sarcomas.
CAP soft tissue protocol. This protocol, version 4.2.0.0 from 2024, covers most sarcomas. It does not list biphenotypic sinonasal sarcoma among the tumors it covers.

Most reports for biphenotypic sinonasal sarcoma therefore do not include a pTNM stage. If your report does include one, the pathologist has used one of these protocols, and the stage reflects the tumor’s size and the structures it has grown into. Your care team relies instead on the tumor extension, the margins, and your scans to plan treatment.

What is the prognosis for biphenotypic sinonasal sarcoma?

The prognosis for biphenotypic sinonasal sarcoma is generally good. Most people are alive and well years after treatment, and deaths caused by the tumor are rare. When they do occur, they usually result from growth into the base of the skull or brain.

The main concern is that the tumor can grow back in the same place, which is called local recurrence. About 1 in 4 to 1 in 2 people have a local recurrence, depending on the group studied. Recurrence can happen many years after treatment, sometimes more than 9 years later, and some people have more than one recurrence.

Spread to other parts of the body (metastasis) is extremely rare. A single case of spread to the lung has been reported. Doctors do not yet know which features on the pathology report best predict whether the tumor will return.

What happens after the diagnosis of biphenotypic sinonasal sarcoma?

Once biphenotypic sinonasal sarcoma has been confirmed, the next steps depend on the findings in your report. The most important factors are tumor extension, margins, and whether the entire tumor was removed. Your care team often includes an ear, nose, and throat surgeon working with a skull base surgeon or neurosurgeon. A radiation oncologist and a medical oncologist with experience in sarcoma are also often involved. Treatment and follow-up options include:

Surgery. Surgery is the main treatment for biphenotypic sinonasal sarcoma, and it is usually performed through the nostrils with an endoscope. A combined approach through the skull may be considered when the tumor has grown into the base of the skull.
Radiation therapy. Radiation may be considered after surgery when the margins are positive or when some tumor could not be removed. Its benefit for this tumor has not yet been clearly established.
Chemotherapy. Chemotherapy is rarely used because this low-grade tumor seldom spreads beyond the nose and sinuses.
Follow-up. Regular examinations with a nasal endoscope and MRI scans look for recurrence. Because recurrence can occur many years later, follow-up usually continues for a long time.

Because biphenotypic sinonasal sarcoma is rare, your care team may also discuss whether a clinical trial or review at a specialized sarcoma center is right for you.

Questions to ask your doctor

Was a PAX3 change found in my tumor, and which test was used?
Does my report include a stage, and if so, which system was used?
Which stains were performed, and did they support the diagnosis?
How large was the tumor, and was the size measured on the specimen or on a scan?
Has the tumor grown into the eye socket, the base of the skull, or the dura?
Were the margins negative or positive, and how close was the tumor to the nearest margin?
Was the tumor removed in pieces, and could the margins be assessed?
Does my report describe the tumor as low grade?
Do I need radiation therapy after surgery?
How often will I need nasal endoscopy and MRI scans, and for how many years?
What symptoms could mean the tumor has come back?
Should my case be reviewed at a sarcoma center, and is there a clinical trial I could join?