SMARCB1-deficient sinonasal carcinoma

by Jason Wasserman MD PhD FRCPC
May 1, 2023

What is SMARCB1-deficient sinonasal carcinoma?

SMARCB1-deficient sinonasal carcinoma is a rare type of cancer that starts in the nasal cavity or one of the paranasal sinuses. It is an aggressive tumour that quickly grows into surrounding organs and tissues in the head. Other names for this type of cancer include INI1-deficient sinonasal carcinoma and SWI/SNF-deficient sinonasal carcinoma.

Nasal cavity and paranasal sinuses

What does SMARCB1-deficient mean?

SMARCB1-deficient means that tumour cells are not producing a protein called SMARCB1 (also known as INI1) which is normally produced by cells throughout the body. The loss of the SMARCB1 protein results from a mutation in the SMARCB1 gene.

Where does SMARCB1-deficient sinonasal carcinoma start?

SMARCB1-deficient sinonasal carcinoma can start anywhere along the sinonasal tract which includes the nasal cavity, maxillary sinus, ethmoid sinus, and sphenoid sinus.

What causes SMARCB1-deficient sinonasal carcinoma?

SMARCB1-deficient sinonasal carcinoma results from a mutation in the SMARCB1 gene, leading to the loss of normal SMARCB1 protein production. What causes this mutation to occur is still unknown.

What are the symptoms of SMARCB1-deficient sinonasal carcinoma?

The symptoms of SMARCB1-deficient sinonasal carcinoma depend on the location and size of the tumour. Most patients will experience non-specific symptoms such as nasal obstruction, facial pain (especially over the sinuses), headaches, and recurrent nose bleeds.

Is SMARCB1-deficient sinonasal carcinoma an aggressive type of cancer?

Yes. SMARCB1-deficient sinonasal carcinoma is an aggressive type of cancer that commonly grows into tissues surrounding the sinonasal tract including the orbits, base of skull, and brain. It is also common for tumour cells to spread to lymph nodes in the neck.

How is the diagnosis of SMARCB1-deficient sinonasal carcinoma made?

The diagnosis can only be made after a sample of the tumour is examined under the microscope by a pathologist. Additional tests such as immunohistochemistry (IHC), next-generation sequencing (NGS), or fluorescence in situ hybridization (FISH) may also be performed to confirm the diagnosis.

What does SMARCB1-deficient sinonasal carcinoma look like under the microscope?

When examined under the microscope, the tumour is made up of large atypical (abnormal) looking cells. The cells may be described as basaloid which means they have a large nucleus and appear more blue than other cells. The chromatin (genetic material) inside the nucleus may be described as vesicular which means it is grouped into multiple small round groups. Larger groups of chromatin called nucleoli may also be seen. Mitotic figures (tumour cells dividing to create new cells) are found throughout the tumour. A type of cell death called necrosis is also commonly seen throughout the tumour.

SMARCB1 deficient sinonasal carcinoma
SMARCB1 deficient sinonasal carcinoma. This picture shows a tumour made up of abnormal epithelial cells arranged in sheets.

When immunohistochemistry is performed, the tumour cells in SMARCB1-deficient sinonasal carcinoma are typically strongly positive for pan-cytokeratin and variably positive (some of the cells are positive) for cytokeratin 5, p40, p63, chromogranin, and synaptophysin. By immunohistochemistry, the tumour cells should show complete loss of SMARCB1 (INI1) protein.

SMARCB1 deficient sinonasal carcinoma INI
SMARCB1 deficient sinonasal carcinoma. This picture shows a loss of INI1 protein in the tumour cells. Normal INI1 expression can be seen in the blood vessels.
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