Keratinizing Squamous Cell Carcinoma of the Nasal Cavity and Sinuses: Understanding Your Pathology Report

by Jason Wasserman MD PhD FRCPC
July 7, 2026

Keratinizing squamous cell carcinoma (KSCC) is a type of cancer that begins in squamous cells, the flat cells lining the inner surfaces of the nasal cavity and paranasal sinuses. The nasal cavity is the hollow space inside the nose that warms, moistens, and filters the air we breathe. The paranasal sinuses, which include the maxillary, frontal, sphenoid, and ethmoid sinuses, are air-filled spaces within the bones around the nose that help lighten the skull and produce mucus to keep the nasal passages moist.

Keratinizing squamous cell carcinoma is the most common type of nasal cavity and sinus cancer and is seen more often in men. In this type of cancer, the tumor cells produce keratin, a tough protein normally found in skin and hair. This feature distinguishes it from a related tumor called nonkeratinizing squamous cell carcinoma. 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 keratinizing squamous cell carcinoma?

Keratinizing squamous cell carcinoma of the nasal cavity and sinuses develops from a combination of environmental, lifestyle, and biological factors.

Occupational exposures — Long-term exposure to certain workplace substances, including nickel, chromium, arsenic, formaldehyde, welding fumes, leather dust, glues, and compounds used in textiles, is linked to this cancer. These exposures explain in part why the cancer is more common in men, and they account for roughly 30% of cases.
Cigarette smoking — Smoking is a well-documented cause, and tobacco use meaningfully increases the risk.
Chronic inflammation — Persistent inflammation in the nasal cavity or sinuses, such as that caused by long-standing sinus infections, may make this cancer more likely to develop.

What are the symptoms?

The symptoms of keratinizing squamous cell carcinoma of the nasal cavity and sinuses depend on the size and location of the tumor. Common symptoms include nasal congestion or a blocked nose, persistent nosebleeds, facial pain or pressure, swelling or a lump in the nasal area, and difficulty breathing through the nose. Some people notice a change in their sense of smell or taste. In advanced cases, unexplained weight loss may occur. Because many of these symptoms overlap with far more common and less serious conditions such as sinus infections, the diagnosis often requires additional testing before it is made.

How is the diagnosis made?

The diagnosis of keratinizing squamous cell carcinoma of the nasal cavity and sinuses 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 tissue is removed from inside the nose or sinus using an endoscope (a thin scope passed through the nostril). If the tumor is later removed in full, the pathologist also examines the larger specimen.

Under the microscope, keratinizing squamous cell carcinoma consists of abnormal epithelial cells that show squamous differentiation, meaning they resemble the flat squamous cells found in normal tissue but with abnormal features. The tumor cells have a glassy, pink cytoplasm (the part of the cell surrounding the nucleus) and are joined by thin connections called intercellular bridges. They frequently produce keratin, which can collect into small round structures called keratin pearls. The presence of keratin is what defines this tumor as the keratinizing type. Several rare variants exist, including papillary, verrucous, spindle cell, acantholytic, adenosquamous, and carcinoma cuniculatum types, each of which is seen in only a small number of cases.

Unlike squamous cell carcinoma of the oropharynx, where testing for human papillomavirus (HPV) using the p16 stain is routine, HPV testing is not a standard part of the workup for keratinizing squamous cell carcinoma of the nasal cavity and sinuses, because this tumor is usually not caused by HPV. Once the diagnosis is confirmed, imaging studies such as CT and MRI are used to assess the size of the tumor and whether it has spread to nearby structures.

Histologic grade

The grade of keratinizing squamous cell carcinoma describes how closely the tumor cells resemble normal squamous cells. Pathologists assign the grade by examining three features under the microscope: how closely the tumor cells resemble normal squamous cells (differentiation), how much the cells vary in size and shape (pleomorphism), and how many cells are actively dividing (mitotic activity). The grade helps predict how the tumor is likely to behave and, together with the tumor’s size and stage, guides treatment planning.

Well differentiated — The tumor cells closely resemble normal squamous cells and produce abundant keratin. This grade is uncommon.
Moderately differentiated — The cells are less like normal squamous cells and produce moderate amounts of keratin. Most keratinizing squamous cell carcinomas fall into this category.
Poorly differentiated — The cells look very abnormal and produce little keratin. These tumors tend to grow and spread more readily than well-differentiated tumors.

Perineural invasion

In keratinizing squamous cell carcinoma of the nasal cavity and sinuses, 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 is important because cancer cells can use nerves as a pathway to invade nearby tissues, which increases 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 keratinizing squamous cell carcinoma were seen 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 tumors in the nasal cavity and sinuses are sometimes removed in more than one piece, the pathologist may not be able to assess every margin in every case.

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. Even when margins are negative, 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. Cancer cells from a keratinizing squamous cell carcinoma of the nasal cavity and sinuses can travel through lymphatic vessels to reach these nodes. When lymph nodes are removed during surgery, often in a procedure called a neck dissection, 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. 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. In cancers of the nasal cavity and sinuses, extranodal extension is used to determine the nodal stage and may influence decisions about additional treatment such as radiation therapy.

Biomarker and molecular testing

Biomarker testing is not a routine part of the workup for every keratinizing squamous cell carcinoma of the nasal cavity and sinuses, but one test becomes relevant when the cancer is advanced, has come back after treatment, or has spread to distant sites.

PD-L1

PD-L1 (programmed death-ligand 1) is a protein that some cancer cells express on their surface to evade immune recognition. Drugs called immune checkpoint inhibitors block this protein, allowing the immune system to recognize and attack the cancer. In squamous cell carcinomas of the head and neck, PD-L1 testing helps identify patients who may benefit from these drugs when the cancer is recurrent or metastatic.

PD-L1 is measured by immunohistochemistry, a test that uses a specially labeled antibody to detect the protein in tumor tissue. For head and neck cancers, the result is usually reported as a Combined Positive Score (CPS), which reflects PD-L1 staining on both the cancer cells and nearby immune cells. A higher score indicates a greater chance that immunotherapy will be effective. Your report will describe the score and whether it is above or below the threshold used for treatment decisions. A CPS of 1 or higher is generally used to identify patients who may be eligible for the immune checkpoint inhibitor pembrolizumab (Keytruda) in recurrent or metastatic disease. A result below the threshold does not rule out immunotherapy in every situation, but it makes eligibility less likely. Evidence on PD-L1 specifically in keratinizing squamous cell carcinoma of the nasal cavity and sinuses is still developing, and your medical oncology team will explain how the result applies to your situation. You can read more in the PD-L1 testing overview and in the full Biomarkers and Molecular Testing section.

Pathologic stage (pTNM)

The pathologic stage for keratinizing squamous cell carcinoma of the nasal cavity and sinuses 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 maxillary sinus versus those that start in the nasal cavity or ethmoid sinus.

Tumor stage (pT) — maxillary sinus

Tis — The cancer is “in situ,” confined to the surface layer and has not invaded deeper tissue.
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 (wing-shaped bones at the base of the skull).
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 socket that holds the eye), 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 (a bony shelf at the top of the nasal cavity), 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) — nasal cavity and ethmoid sinus

Tis — The cancer is “in situ,” confined to the surface layer.
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 maxillary sinus, the palate (the roof of the mouth), or the cribriform plate.
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, or nearby bones.
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, or deep areas of the skull.

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. For keratinizing squamous cell carcinoma of the nasal cavity and sinuses, the outlook depends mainly on where the tumor started and how far it had spread by the time it was found. The overall five-year survival rate is approximately 50%, and survival varies considerably by location.

Nasal cavity — Tumors that start here have the most favorable outlook, with roughly 74% of patients surviving five years after diagnosis.
Maxillary and ethmoid sinuses — Tumors in these locations have a five-year survival rate of about 35%.
Frontal and sphenoid sinuses — Tumors here have the least favorable outlook, with five-year survival below 30%, in part because they are often found at a more advanced stage.

Other findings on the pathology report also affect the outlook. A higher grade, a higher tumor stage, involvement of lymph nodes, extranodal extension, perineural invasion, lymphovascular invasion, and positive surgical margins are each associated with a higher risk of the cancer returning after treatment.

What happens after the diagnosis?

Treatment for keratinizing squamous cell carcinoma of the nasal cavity and sinuses 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. The approach is guided by the location, size, and stage of the tumor, along with the specific findings in the pathology report.

Surgery is the main treatment for tumors that can be removed. Depending on the extent of disease, surgery may be performed endoscopically through the nose or through a larger open approach involving the face and skull base. The goal is complete removal of the tumor with clear margins. When the report shows positive or close margins, perineural invasion, lymphovascular invasion, or cancer in the lymph nodes, radiation therapy after surgery may be considered, and these specific findings directly inform that decision. For advanced disease, chemotherapy may be added, and for recurrent or metastatic tumors, immunotherapy may be an option depending on the PD-L1 result. After treatment, regular follow-up with imaging and physical examination is used to watch for any sign of the cancer returning.

Questions to ask your doctor

Where exactly did my cancer start — the nasal cavity, maxillary sinus, or ethmoid sinus?
What is the grade of my tumor, and what does that mean for how it may behave?
What is my pathologic stage (pT and pN), and what does that mean for my treatment?
Were the surgical margins negative, and does the report suggest the tumor was completely removed?
Was perineural invasion present in my tumor?
Was lymphovascular invasion present in my tumor?
Were lymph nodes examined, and did any contain cancer cells? Was extranodal extension present?
Was PD-L1 testing performed, and if so, what was the result?
Will I need radiation therapy after surgery, and which findings in my report influenced that recommendation?
What signs of recurrence should I watch for, and how will I be monitored after treatment?
Are there any clinical trials available for my type of cancer?