SWI/SNF Complex-Deficient Sinonasal Carcinoma: Understanding Your Pathology Report

Section Editor: Jason Wasserman MD PhD FRCPC
October 27, 2026

SWI/SNF complex-deficient sinonasal carcinoma is a rare, fast-growing type of cancer that starts in the nasal cavity or the sinuses. The tumor cells have lost one of the proteins that make up a group called the SWI/SNF complex. Pathologists confirm the diagnosis by showing that the tumor cells lack this protein.

Two types of SWI/SNF complex-deficient sinonasal carcinoma exist. The more common type has lost a protein called SMARCB1, also known as INI1. The less common type has lost a protein called SMARCA4, also known as BRG1. Both types were once diagnosed as other cancers, such as sinonasal undifferentiated carcinoma or neuroendocrine carcinoma, before testing for these proteins became routine.

This article explains what SWI/SNF complex-deficient sinonasal carcinoma is, how the two types differ, and what the findings in your pathology report mean for your care.

Who gets SWI/SNF complex-deficient sinonasal carcinoma?

SWI/SNF complex-deficient sinonasal carcinoma is most commonly found in adults. People with the SMARCB1-deficient type are typically diagnosed in their 50s. People with the SMARCA4-deficient type tend to be younger, typically in their early 40s. About 2 in 3 people with either type are men.

The tumor most often starts in the nasal cavity or the ethmoid sinuses, the small air spaces between the eyes. By the time it is found, it often involves several sinuses.

What causes SWI/SNF complex-deficient sinonasal carcinoma?

SWI/SNF complex-deficient sinonasal carcinoma is caused by a change in one of the genes that build the SWI/SNF complex. This complex is a group of proteins that controls which genes in a cell are switched on or off. It does this by loosening or tightening the way DNA is packed inside the cell.

SMARCB1 and SMARCA4 normally act as tumor suppressors, meaning they help stop cells from growing out of control. When a gene change removes one of these proteins, the cell loses that control and can grow into a tumor. These changes develop in tumor cells during a person’s life.

Unlike some other cancers of the nose, SWI/SNF complex-deficient sinonasal carcinoma has not been linked to infection with human papillomavirus or Epstein-Barr virus. No other clear risk factors have been identified.

What are the symptoms of SWI/SNF complex-deficient sinonasal carcinoma?

The symptoms of SWI/SNF complex-deficient sinonasal carcinoma are caused by a mass growing inside the nose and sinuses. Because the tumor grows quickly, symptoms can appear and worsen quickly. Common symptoms include:

A blocked or stuffy nose.
Nosebleeds.
Headache.
Bulging of the eye or changes in vision, when the tumor grows into the eye socket.

How is the diagnosis of SWI/SNF complex-deficient sinonasal carcinoma made?

The diagnosis of SWI/SNF complex-deficient sinonasal carcinoma 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.

Under the microscope, the tumor consists of sheets and nests of cancer cells that do not resemble normal nasal tissue. In the SMARCB1-deficient type, the cells are often small and dark, a pattern called basaloid. Some tumors instead have larger cells with a pink cytoplasm pushed to one side, described as rhabdoid or plasmacytoid. The SMARCA4-deficient type is usually made of large cells with areas of dead tumor, called necrosis.

Because these features overlap with other cancers of the nose, immunohistochemistry confirms the diagnosis. The key result is the loss of either SMARCB1 or SMARCA4 in tumor cells, as described in the next section.

Once the diagnosis is confirmed, CT and MRI scans of the head and neck show how far the tumor has spread. Chest scans or a PET scan may also be used to look for spread to other parts of the body.

Immunohistochemistry

Immunohistochemistry is the main test used to diagnose SWI/SNF complex-deficient sinonasal carcinoma. Immunohistochemistry uses antibodies to show which proteins are present in the tumor cells. The pathologist looks for a missing SWI/SNF protein and uses other stains to rule out similar cancers. Results that may appear in your report include:

SMARCB1 (INI1). Reported as lost, absent, or deficient in the SMARCB1-deficient type. In the SMARCA4-deficient type, SMARCB1 is retained, meaning the protein is still present.
SMARCA4 (BRG1). Reported as lost, absent, or deficient in the SMARCA4-deficient type. In the SMARCB1-deficient type, SMARCA4 is usually retained.
Cytokeratins. Positive in both types. Cytokeratins are proteins made by epithelial cells, and a positive result shows that the tumor is a carcinoma.
p40 and p63. Positive in more than half of SMARCB1-deficient tumors. These proteins are found in squamous and basal cells, and p63 is usually negative in the SMARCA4-deficient type.
Synaptophysin and chromogranin. These neuroendocrine markers are positive in some tumors, often only in a few cells. They are seen more often in the SMARCA4-deficient type and can make it look like a neuroendocrine carcinoma.
NUT. Negative. A positive result would point instead to NUT carcinoma, a different cancer that can look similar.

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

What are the different types of SWI/SNF complex-deficient sinonasal carcinoma?

The 5th edition of the World Health Organization (WHO) classification of head and neck tumors, published in 2022, divides SWI/SNF complex-deficient sinonasal carcinoma into two types. The type is named for the protein that is missing from the tumor cells:

SMARCB1-deficient sinonasal carcinoma. This is the more common type. The tumor cells have lost SMARCB1, and they often look basaloid or rhabdoid under the microscope. Our article on SMARCB1-deficient sinonasal carcinoma describes this type in more detail.
SMARCA4-deficient sinonasal carcinoma. This type is less common and tends to affect younger adults. The tumor cells have lost SMARCA4 and often show some neuroendocrine features. In the past, many of these tumors were diagnosed as neuroendocrine carcinoma or teratocarcinosarcoma.

Older reports, written before the 2022 WHO classification, may use names such as SMARCB1-deficient carcinoma, INI1-deficient carcinoma, or sinonasal undifferentiated carcinoma for these tumors.

Histologic grade

SWI/SNF complex-deficient sinonasal carcinoma is not given a histologic grade. Many carcinomas are graded as well, moderately, or poorly differentiated, depending on how much they resemble normal tissue. This tumor is defined by its missing protein rather than its appearance, and it behaves as a high-grade cancer.

The College of American Pathologists (CAP) protocol for the nasal cavity and sinuses notes that some newer tumor types, defined by specific genetic changes, do not need a grade. Your report may therefore say that grade is not applicable, or it may not mention grade at all.

Perineural invasion

Perineural invasion means cancer cells are seen along or inside a nerve. In SWI/SNF complex-deficient sinonasal carcinoma, nerves near the skull base can give the tumor a path to spread toward the brain. Your report will say whether perineural invasion was identified, not identified, or could not be determined.

Lymphovascular invasion

Lymphovascular invasion means cancer cells are seen inside a blood vessel or lymphatic channel. In SWI/SNF complex-deficient sinonasal carcinoma, this finding raises concern that tumor cells could travel to lymph nodes or other organs. Your report will say whether lymphovascular invasion was identified, not identified, or could not be determined.

Surgical margins

A margin is the edge of tissue the surgeon cuts to remove the tumor. Margins are described only when SWI/SNF complex-deficient sinonasal carcinoma has been removed by surgery, not on a biopsy. Your report will describe them as follows:

Negative margin. No cancer cells are seen at the cut edge. Your report will also give the distance in millimeters (mm) from the cancer to the closest margin.
Positive margin. Cancer cells are seen at the cut edge. This means some cancer may remain, and your care team may consider further surgery or radiation therapy.
Cannot be determined. The margins could not be assessed. This happens most often when the tumor is removed in several pieces during endoscopic surgery.

Lymph nodes

Lymph nodes are small immune organs that filter fluid from the tissues. In SWI/SNF complex-deficient sinonasal carcinoma, spread to lymph nodes in the neck is found in fewer than 1 in 10 people at diagnosis. Lymph nodes are removed in an operation called a neck dissection when scans show they may contain cancer.

When lymph nodes are examined, your report will say how many were removed and how many contain cancer cells. It will also give the size of the largest group of cancer cells in a lymph node. The report will also state whether extranodal extension is present, meaning cancer cells have broken through the lymph node’s outer capsule into surrounding tissue. Extranodal extension increases the nodal stage and is one of the findings your care team considers when planning treatment after surgery.

Biomarker and molecular testing

For SWI/SNF complex-deficient sinonasal carcinoma, no established biomarker tests currently guide the choice of a specific targeted drug. The loss of SMARCB1 or SMARCA4 is used for diagnosis, as described in the immunohistochemistry section above. Some laboratories also confirm the gene change using next-generation sequencing (NGS).

Researchers have studied drugs called EZH2 inhibitors in tumors that have lost SMARCB1. One of these, tazemetostat, received accelerated approval from the US Food and Drug Administration (FDA) for other cancers but never for sinonasal carcinoma. Its manufacturer withdrew it from all markets in March 2026 because of a safety concern. You may still see it mentioned in older articles about this tumor.

Research into other treatments that target SWI/SNF loss is ongoing. Your oncologist can tell you whether a clinical trial or broader molecular testing is appropriate in your situation. More information is available in our Biomarkers and Genetic Testing section.

Pathologic stage (pTNM)

The pathologic stage for SWI/SNF complex-deficient sinonasal carcinoma uses the TNM system in the AJCC Cancer Staging Manual, 8th edition. The pTNM stage combines the tumor stage (pT) and the nodal stage (pN). Imaging rather than the pathology report usually determines the metastasis stage (M).

Tumor stage (pT)

The tumor stage for SWI/SNF complex-deficient sinonasal carcinoma depends on where the tumor started. Because most of these tumors have grown into nearby structures by the time they are found, the majority are pT4.

Nasal cavity and ethmoid sinus:

pT1. The tumor is limited to one area of the nasal cavity or ethmoid sinus, with or without bone invasion.
pT2. The tumor involves two areas of the nasal cavity or ethmoid sinus, or extends into a neighboring area, with or without growth into bone.
pT3. The tumor has grown into the floor or inner wall of the eye socket, the maxillary sinus, or the roof of the mouth. It may instead involve the cribriform plate, the thin bone below the brain.
pT4a. The tumor has grown into the front of the eye socket, the skin of the nose or cheek, or slightly into the front of the skull. It may instead have reached the pterygoid plates or the sphenoid or frontal sinuses.
pT4b. The tumor has grown into the back of the eye socket, the dura covering the brain, the brain itself, or the middle of the skull base. It may instead involve certain cranial nerves, the nasopharynx, or the clivus.

Maxillary sinus:

pT1. The tumor is limited to the lining of the maxillary sinus, with no damage to the bone.
pT2. The tumor has damaged the sinus bone or grown into the roof of the mouth or the middle part of the nasal cavity.
pT3. The tumor has grown into the back wall of the sinus, the tissue under the skin, or the floor or inner wall of the eye socket. It may instead involve the pterygoid fossa or the ethmoid sinuses.
pT4a. The tumor has grown into the front of the eye socket, the skin of the cheek, or the pterygoid plates. It may instead involve the infratemporal fossa, the cribriform plate, or the sphenoid or frontal sinuses.
pT4b. The tumor has grown into the back of the eye socket, the dura, the brain, or the middle of the skull base. It may instead involve certain cranial nerves, the nasopharynx, or the clivus.

If the tumor stage cannot be assessed, for example because the tumor was removed in many small pieces, your report may say that the pT stage was not assigned.

Nodal stage (pN)

pN0. No cancer cells are found in the examined lymph nodes.
pN1. Cancer is found in one lymph node on the same side as the tumor. The node is 3 cm or smaller, with no extranodal extension.
pN2a. Cancer is found in one lymph node on the same side. Either it is 3 cm or smaller with extranodal extension, or it is larger than 3 cm but not larger than 6 cm without extranodal extension.
pN2b. Cancer is found in more than one lymph node on the same side, none larger than 6 cm and none with extranodal extension.
pN2c. Cancer is found in lymph nodes on the opposite side or on both sides, none larger than 6 cm and none with extranodal extension.
pN3a. Cancer is found in a lymph node larger than 6 cm, without extranodal extension.
pN3b. Cancer is found in a lymph node with extranodal extension, other than the single small node described under pN2a.
pNX. Lymph nodes were not examined.

Your care team combines the pT stage, the pN stage, and your scans to assign an overall stage group from stage I to stage IV. A tumor that is pT4a is at least stage IVA, and a tumor that is pT4b is stage IVB. Cancer that has spread to distant organs is stage IVC.

What is the prognosis for SWI/SNF complex-deficient sinonasal carcinoma?

SWI/SNF complex-deficient sinonasal carcinoma is a serious cancer, and the prognosis is guarded. Because it is rare, most of what we know comes from small patient groups. For the SMARCB1-deficient type, about 6 in 10 people are alive 2 years after diagnosis, and about half are alive at 3 years.

Less is known about the SMARCA4-deficient type. Some reports describe very short survival of only months, while larger combined analyses find outcomes similar to the SMARCB1-deficient type. About 1 in 3 people with either type develop metastasis (spread to distant organs) at some point. The lungs, bones, and brain are the most common sites.

The tumor stage in the pathology report is the finding most strongly linked to outcome. A pT4b tumor has grown into the brain, the dura, or the back of the eye socket. People with a pT4b tumor have a poorer outlook than people with smaller tumors. Your care team can explain what your report findings mean for your outlook.

What happens after the diagnosis of SWI/SNF complex-deficient sinonasal carcinoma?

Once SWI/SNF complex-deficient sinonasal carcinoma has been confirmed, the next steps depend on the type, the tumor stage, and how far the tumor has spread. Your care team usually includes a head and neck surgeon, often with a skull base surgeon or neurosurgeon. A radiation oncologist and a medical oncologist are also involved. Treatment usually combines more than one approach:

Surgery. When the tumor can be removed safely, surgery is often part of treatment. It may be performed through the nostrils with an endoscope, or through an open approach when the tumor involves the skull base.
Radiation therapy. Radiation therapy is part of treatment for most people, usually after surgery. The team considers findings such as positive margins, perineural invasion, or lymph node spread when planning it.
Chemotherapy. Chemotherapy is often given, sometimes before surgery or radiation to shrink the tumor. It may also be combined with radiation therapy.
Clinical trials. Because this cancer is rare and new treatments are being studied, your care team may discuss whether a clinical trial is right for you.

After treatment, regular examinations with a nasal endoscope and scans are used to look for any sign that the cancer has returned.

Questions to ask your doctor

Is my tumor the SMARCB1-deficient type or the SMARCA4-deficient type?
Which stains were used to confirm the diagnosis, and was any other cancer ruled out?
Was my tumor previously called a different name, such as sinonasal undifferentiated carcinoma?
Where did the tumor start, and which structures has it grown into?
What is the pT stage, and what is my overall stage group?
Was perineural invasion or lymphovascular invasion identified?
Were the margins negative or positive, and how close was the cancer to the nearest margin?
Were any lymph nodes examined, and did any contain cancer or show extranodal extension?
Do my scans show spread to other parts of my body?
Which combination of surgery, radiation therapy, and chemotherapy is being considered for me?
Is there a clinical trial I could join?
How often will I need endoscopy and scans after treatment?