by Jason Wasserman MD PhD FRCPC
September 8, 2022
Non-intestinal-type sinonasal adenocarcinoma (SNAC) is a rare type of head and neck cancer. The tumour starts from the tissue that lines the inside of the nasal cavity or the paranasal sinuses such as the ethmoid or maxillary sinus. Pathologists divide non-intestinal-type SNAC into two grades, low and high, with high-grade tumours being associated with more aggressive behaviour and worse overall outcome.
At present, doctors do not know what causes non-intestinal-type SNAC. Rare tumours have been associated with human papillomavirus (HPV) but this virus is not believed to cause most non-intestinal-type SNACs.
The diagnosis of non-intestinal-type SNAC is usually made after a small sample of tissue is removed in a procedure called a biopsy. The diagnosis can also be made after the entire tumour is removed in a procedure called a resection. The tissue is then sent to a pathologist who examines it under a microscope.
Pathologists divide non-intestinal-type SNAC into two grades, high and low, based on the way the tumour cells look when examined under the microscope. The grade is important because low grade tumours may grow into surrounding tissues but are more likely to be cured by surgery alone. In contrast, high grade tumours grow more quickly and are more likely to spread to other parts of the body such as lymph nodes in the neck.
Low grade tumours are made up of medium-sized cells that contain a specialized type of protein called mucin. The tumour cells often connect together to form round structures called glands or long finger-like projections called papillae. The glands may be arranged in a back-to-back manner that pathologists describe as cribriform. Dividing cells called mitotic figures and a type of cell death called necrosis are rarely seen in low grade non-intestinal-type SNAC.
High grade tumours are often made up of larger more abnormal-looking cells that contain less mucin than low-grade tumours. Pathologists use the word atypical to describe abnormal-looking cells. The tumour cells are often connected together into large groups that pathologists describe as a solid pattern of growth. Unlike low-grade tumours, dividing tumour cells called mitotic figures and a type of cell death called necrosis are commonly seen.
Your pathologists may perform a test called immunohistochemistry to confirm the diagnosis. When performed, the tumour cells in non-intestinal-type SNAC are usually positive for specialized proteins called cytokeratins including CK7. Very rarely the tumour cells may be positive for proteins normally seen in the gastrointestinal tract such as CK20. High-grade non-intestinal-type SNACs may produce proteins made by neuroendocrine cells such as chromogranin and synaptophysin.
Low grade non-intestinal-type SNACs very rarely metastasize (spread) to lymph nodes or other parts of the body and are cured by surgery alone. High grade non-intestinal-type SNACs are more likely to metastasize to other parts of the body, however, the overall risk is still low.
Perineural invasion means that tumour cells were seen attached to a nerve. Nerves are found all over the body and they are responsible for sending information (such as temperature, pressure, and pain) between your body and your brain. Perineural invasion is important because tumour cells that have become attached to a nerve can spread into surrounding tissues by growing along the nerve. This increases the risk that the tumour will regrow after treatment.
Lymphovascular invasion means that tumour cells were seen inside of a blood vessel or lymphatic vessel. Blood vessels are long thin tubes that carry blood around the body. Lymphatic vessels are similar to small blood vessels except that they carry a fluid called lymph instead of blood. Lymphovascular invasion is important because these cells are able to metastasize (spread) to other parts of the body such as lymph nodes or the lungs.
A margin is any tissue that was cut by the surgeon in order to remove the tumour from your body. Whenever possible, surgeons will try to cut tissue outside of the tumour to reduce the risk that any cancer cells will be left behind after the tumour is removed.
The types of margins described in your report will depend on the parts of the sinonasal tract involved and the type of surgery performed. Margins are usually only described in your report after the entire tumour has been removed.
A negative margin means that no tumour cells were seen at any of the cut edges of tissue. A margin is called positive when there are tumour cells at the very edge of the cut tissue. A positive margin is associated with a higher risk that the tumour will recur in the same site after treatment.
Because non-intestinal-type SNAC is often removed in multiple pieces, your pathologist may not be able to reliably assess the margins of the tumour. For that reason, most pathology reports for non-intestinal-type SNAC do not have information about margins.
Lymph nodes are small immune organs located throughout the body. Tumour cells can travel from the tumour to a lymph node through lymphatic channels located in and around the tumour (see Lymphovascular invasion above). The movement of tumour cells from the tumour to a lymph node is called metastasis.
Your pathologist will carefully examine each lymph node for tumour cells. Lymph nodes that contain tumour cells are often called positive while those that do not contain any tumour cells are called negative. Most reports include the total number of lymph nodes examined and the number, if any, that contain tumour cells.
The pathologic stage for non-intestinal-type SNAC is based on the TNM staging system, an internationally recognized system originally created by the American Joint Committee on Cancer. This system uses information about the primary tumour (pT), lymph nodes (pN), and distant metastatic disease (pM) to determine the complete pathologic stage (pTNM). Your pathologist will examine the tissue submitted and give each part a number. In general, a higher number means more advanced disease and a worse prognosis.
These tumours are given a tumour stage between 1 and 4. The tumour stage is based on how far the tumour has spread outside of the nasal cavity or ethmoid sinus.
These tumours are given a tumour stage between 1 and 4. The tumour stage is based on how far the tumour has spread outside of the maxillary sinus.
These tumours are given a nodal stage between 0 and 3 based on the following three features:
The nodal stage will be higher if any of the tumour deposits are larger than 3 cm, more than one lymph node contains cancer cells, cancer cells are found in lymph nodes on both sides of the neck, and if any of the lymph nodes show extranodal extension.
If no cancer cells are found in any of the lymph nodes examined, the nodal stage is N0. If no lymph nodes are submitted for pathological examination, the nodal cannot be determined and the stage is listed as NX.
Non-intestinal-type SNAC is given a metastatic stage (pM) of 0 or 1 based on the presence of cancer cells at a distant site in the body (for example the lungs). The metastatic stage can only be determined if tissue from a distant site is submitted for pathological examination. Because this tissue is rarely present, the metastasis stage cannot be determined and is listed as MX.