SMARCB1-Deficient Sinonasal Carcinoma: Understanding Your Pathology Report

by Jason Wasserman MD PhD FRCPC
July 10, 2026

SMARCB1-deficient sinonasal carcinoma is a rare, fast-growing cancer that starts in the nasal cavity or one of the paranasal sinuses, an area of the body called the sinonasal tract. The paranasal sinuses are air-filled spaces in the bones around the nose. The name indicates that the tumor cells have lost a protein called SMARCB1 (also known as INI1), and this loss defines the tumor. You may also see this cancer called INI1-deficient sinonasal carcinoma or SWI/SNF-deficient sinonasal carcinoma, which are other names for the same tumor. It is a high-grade cancer that tends to grow quickly into nearby structures. 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 SMARCB1-deficient sinonasal carcinoma?

SMARCB1-deficient sinonasal carcinoma is caused by a change (mutation) in the SMARCB1 gene. Normally, the SMARCB1 gene tells cells how to make the SMARCB1 protein, which helps control cell growth and division. When the gene is altered, the cell stops making a working protein, and the loss of this protein allows the cell to grow out of control. In this tumor, the change in the SMARCB1 gene is usually acquired during a person’s lifetime rather than inherited, and its cause is not yet known.

What are the symptoms?

The symptoms of SMARCB1-deficient sinonasal carcinoma depend on the size and location of the tumor, and they often develop quickly because the tumor tends to grow rapidly. Common symptoms include a blocked or stuffy nose, facial pain or pressure (especially over the sinuses), headaches, and frequent nosebleeds. Because the tumor can grow toward the eye socket or the base of the skull, some people also notice swelling around the eye or changes in vision. These symptoms overlap with common, noncancerous conditions, but their rapid onset often prompts imaging and a biopsy.

How is the diagnosis made?

The diagnosis of SMARCB1-deficient sinonasal carcinoma is made after a tissue sample is examined under the microscope by a pathologist. The sample is usually obtained through a biopsy, in which a small piece of the tumor is removed, typically via an endoscope through the nose. Under the microscope, the tumor consists of large, atypical (abnormal-looking) cells arranged in sheets. The cells are often described as basaloid, meaning they have a large nucleus and appear more blue than normal cells. The chromatin (genetic material inside the nucleus) may be grouped into small round clusters, and larger structures called nucleoli may be seen. Large numbers of mitotic figures (cells caught in the act of dividing) and areas of necrosis (cell death) are commonly seen.

Because this tumor can look like several other sinonasal cancers, additional tests are used to confirm the diagnosis. Immunohistochemistry, a test that uses specially labeled antibodies to detect proteins in the tumor cells, is central to the diagnosis. The tumor cells are usually strongly positive for a group of proteins called cytokeratins, confirming that the tumor is a carcinoma, and they may be variably positive for cytokeratin 5 (CK5), p40, p63, chromogranin, and synaptophysin. The defining feature is that the tumor cells show complete loss of the SMARCB1 (INI1) protein, while nearby normal cells, such as those in blood vessels, retain the protein. This loss is what confirms the diagnosis. In some cases, next-generation sequencing (NGS) or fluorescence in situ hybridization (FISH) is used to confirm the SMARCB1 gene change. Once the diagnosis is confirmed, imaging studies such as CT and MRI are used to determine the size of the tumor and the extent of its spread.

Histologic grade

SMARCB1-deficient sinonasal carcinoma is not assigned a histologic grade in the usual way, because grading is based on how closely the tumor cells resemble normal cells, and the cells of this tumor look very abnormal by definition. For this reason, it is considered a high-grade cancer. Your pathology report will not include a grade number, and this is expected. Being high grade means the tumor tends to grow quickly and is more likely to spread, which is why treatment usually begins soon after the diagnosis is made.

Perineural invasion

In SMARCB1-deficient sinonasal carcinoma, the pathologist looks for perineural invasion, which means cancer cells were seen attached to or growing along the outside of a nerve. Nerves run throughout the head and neck, carrying signals such as temperature, pressure, and pain between the body and the brain. Perineural invasion matters because cancer cells can use nerves as a pathway to travel into surrounding tissues, which raises the risk of the tumor returning after treatment. If perineural invasion is present, it will be described in your pathology report.

Lymphovascular invasion

Lymphovascular invasion means that cancer cells from the SMARCB1-deficient sinonasal carcinoma were observed within a blood or lymphatic vessel. Blood vessels carry blood throughout the body, and lymphatic vessels carry a fluid called lymph. Both types of vessels connect to other parts of the body, so cancer cells that enter them can travel to distant sites such as lymph nodes or the lungs. If lymphovascular invasion is present, it will be included in your pathology report.

Surgical margins

A surgical margin is the edge of the tissue that the surgeon cuts through when removing the tumor. Margins are assessed after a procedure that removes the entire tumor, such as an excision or resection, and are usually not evaluated after a biopsy, which removes only part of the tumor. Because SMARCB1-deficient sinonasal carcinoma often grows into nearby structures and may be removed in more than one piece, the pathologist may not always be able to fully assess the margins.

Negative margin — No cancer cells are present at the cut edge of the tissue. This suggests the tumor was completely removed.
Close margin — Cancer cells are near the cut edge but do not reach it. The distance from the nearest cancer cells to the edge may be measured and reported, because a very close margin can be relevant to decisions about additional treatment.
Positive margin — Cancer cells are present at the cut edge. This means some tumor may remain in the body, and the treatment team will use this finding when considering whether additional surgery or radiation therapy is appropriate.

Lymph nodes

Lymph nodes are small immune organs found throughout the head and neck. SMARCB1-deficient sinonasal carcinoma can spread through lymphatic vessels to reach these nodes, and lymph node involvement is relatively common with this tumor. For this reason, lymph nodes in the neck are sometimes removed at the same time as the main tumor, in a procedure called a neck dissection. When lymph nodes are removed, they are examined under the microscope and the results are described in your pathology report.

Your report will include the total number of lymph nodes examined, the number that contain cancer cells, and the size of the largest deposit of cancer cells (often called a “focus” or “deposit”). A node that contains cancer cells is described as “positive,” and a node with no cancer cells is described as “negative.” The pathologist also checks for extranodal extension, which means cancer cells have broken through the outer capsule of a lymph node and spread into the surrounding tissue. Lymph node findings are used to determine the pathologic nodal stage (pN) and, along with the finding of cancer cells spreading to other parts of the body (metastasis), may influence decisions about additional treatment such as chemotherapy, radiation therapy, or immunotherapy.

Pathologic stage (pTNM)

The pathologic stage for SMARCB1-deficient sinonasal carcinoma is based on the TNM staging system, as defined in the American Joint Committee on Cancer (AJCC) Cancer Staging Manual, 8th edition. This system describes the tumor using three categories: the primary tumor (pT), the regional lymph nodes (pN), and distant spread (pM). In general, a higher stage reflects more advanced disease. The metastatic stage (pM) is determined by imaging and clinical evaluation, not by the pathologist examining the surgical specimen. Because the tumor stage depends on where the cancer began, the criteria differ for tumors that start in the nasal cavity or ethmoid sinus versus those that start in the maxillary sinus.

Tumor stage (pT) — nasal cavity and ethmoid sinus

pT1 — The tumor is limited to one area (subsite) of the nasal cavity or ethmoid sinus, with or without involvement of the surrounding bone.
pT2 — The tumor involves two subsites within the nasal cavity or ethmoid sinus, or extends into an adjacent area within this region, with or without involvement of the surrounding bone.
pT3 — The tumor has invaded the floor or inner wall of the orbit (the socket that holds the eye), the maxillary sinus, the palate (the roof of the mouth), or the cribriform plate (a bony shelf at the top of the nasal cavity).
pT4a — The tumor has grown into the front part of the eye socket, the skin of the nose or cheek, a limited area at the base of the skull, the pterygoid plates (wing-shaped bones at the base of the skull), or the sphenoid or frontal sinuses.
pT4b — The tumor has grown into the deepest part of the eye socket, the coverings of the brain, the brain itself, the middle cranial fossa, specific cranial nerves, the upper throat behind the nose (nasopharynx), or a bony area at the base of the skull (clivus).

Tumor stage (pT) — maxillary sinus

pT1 — The tumor is limited to the lining (mucosa) of the maxillary sinus and has not damaged the surrounding bone.
pT2 — The tumor has eroded or destroyed bone, possibly including the hard palate or the middle nasal passage, but has not reached the back wall of the maxillary sinus or the pterygoid plates.
pT3 — The tumor has invaded the back wall of the maxillary sinus, the tissue beneath the skin, the floor or inner wall of the orbit, the pterygoid fossa (a depression at the side of the skull), or the ethmoid sinuses.
pT4a — The tumor has grown into the front part of the eye socket, the skin of the cheek, the pterygoid plates, the infratemporal fossa (a space at the side of the skull), the cribriform plate, or the sphenoid or frontal sinuses.
pT4b — The tumor has grown into the deepest part of the eye socket, the coverings of the brain, the brain itself, the middle cranial fossa, specific cranial nerves, the nasopharynx, or the clivus.

Nodal stage (pN)

pNX — The lymph nodes could not be assessed.
pN0 — No cancer cells were found in any of the lymph nodes examined.
pN1 — Cancer cells were found in a single lymph node on the same side of the neck as the tumor. The node is 3 cm or smaller and shows no extranodal extension.
pN2a — Cancer cells were found in a single lymph node on the same side of the neck that is either 3 cm or smaller with extranodal extension, or larger than 3 cm but no larger than 6 cm without extranodal extension.
pN2b — Cancer cells were found in more than one lymph node on the same side of the neck. None is larger than 6 cm, and none shows extranodal extension.
pN2c — Cancer cells were found in lymph nodes on both sides of the neck, or on the opposite side from the tumor. None is larger than 6 cm, and none shows extranodal extension.
pN3a — A lymph node containing cancer cells is larger than 6 cm and shows no extranodal extension.
pN3b — A lymph node with extranodal extension is present, or multiple involved nodes show extranodal extension.

What is the prognosis?

Prognosis refers to the likely long-term outcome after a diagnosis. SMARCB1-deficient sinonasal carcinoma is a high-grade cancer that tends to grow quickly and is often found after it has spread into nearby structures or to the lymph nodes, so the outlook has generally been guarded. Because the tumor is rare and was only recognized as a distinct type of cancer in recent years, precise survival figures are still limited, and reported outcomes vary. What is clear is that the stage of the tumor and its response to treatment are the most important factors.

Stage — Tumors that have grown into the orbit, skull base, or brain, or that have spread to lymph nodes or distant sites, carry a higher risk.
Margin status — When surgery is performed, positive or close margins are associated with a higher risk of the tumor returning in the same area.
Perineural and lymphovascular invasion — Either finding is associated with a higher chance that the tumor will spread or return.

What happens after the diagnosis?

Treatment for SMARCB1-deficient sinonasal carcinoma is planned by a multidisciplinary team that may include ear, nose, and throat (ENT) surgeons, neurosurgeons for tumors near the skull base, radiation oncologists, and medical oncologists. Because this tumor grows quickly and is often advanced at diagnosis, treatment usually combines more than one approach.

Many patients receive chemotherapy first, before other treatment, and how the tumor responds helps guide the next steps. Surgery to remove the tumor, when possible, is often followed by radiation therapy, and chemotherapy and radiation may be combined. When surgery is performed, the pathology findings, including margin status, perineural invasion, and lymph node involvement, directly inform whether additional treatment is added. Because this cancer belongs to a family of tumors driven by loss of the SMARCB1 protein, clinical trials of newer targeted drugs, including a class of medicines called EZH2 inhibitors, are being studied, and your oncology team can discuss whether a trial is appropriate for you. After treatment, close follow-up with imaging and physical examination is important, because this tumor can return.

Questions to ask your doctor

Where exactly did my cancer start — the nasal cavity, ethmoid sinus, or maxillary sinus?
How was the diagnosis confirmed, and did my tumor show loss of the SMARCB1 (INI1) protein?
What is my pathologic stage (pT and pN), and what does that mean for my treatment?
Were lymph nodes examined, and did any contain cancer cells? Was extranodal extension present?
Was perineural or lymphovascular invasion present in my tumor?
Will my treatment begin with chemotherapy, and how will my response guide the next steps?
If surgery is done, what will the margin results mean for whether I need more treatment?
Are there clinical trials, including trials of targeted drugs, that I may be eligible for?
What signs of recurrence should I watch for, and how will I be monitored after treatment?
Which specialists will be involved in my care?