Squamous Cell Carcinoma of the Oral Cavity: Understanding Your Pathology Report

by Jason Wasserman MD PhD FRCPC
April 9, 2026

Squamous cell carcinoma is the most common type of cancer in the oral cavity. It starts from squamous cells — the thin, flat cells that form the inner lining of the mouth. The oral cavity includes the lips, the front two-thirds of the tongue, the inner cheeks (buccal mucosa), the floor of the mouth, the gums, the retromolar trigone (the area behind the last molar), and the hard palate. Cancers that arise in any of these areas are collectively referred to as oral cavity 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 are the symptoms?

Early squamous cell carcinoma of the oral cavity may not cause any noticeable symptoms. As the tumor grows, people often notice changes in the mouth that do not heal within two to three weeks. Common symptoms include:

• A sore or ulcer in the mouth that does not heal
• Red, white, or mixed red-white patches (erythroplakia, leukoplakia, or speckled leukoplakia)
• Pain, bleeding, or tenderness in the affected area
• Loose teeth or poorly fitting dentures
• Difficulty chewing, swallowing, or speaking
• Reduced movement of the tongue or jaw
• A lump or swelling in the neck, which may indicate cancer has spread to a lymph node

Any persistent sore, patch, or lump in the mouth should be evaluated by a healthcare professional.

What causes squamous cell carcinoma?

Squamous cell carcinoma of the oral cavity develops when the squamous cells lining the mouth undergo genetic changes that allow them to grow uncontrollably. These changes often result from long-term exposure to substances or conditions that damage the cells.

The main risk factors are tobacco use of any kind, heavy alcohol consumption, betel nut or areca nut chewing, and poor oral hygiene. Chronic irritation from dental appliances or sharp teeth, previous head and neck radiation, and a history of oral precancerous conditions — such as oral epithelial dysplasia, leukoplakia, or erythroplakia — also increase the risk. Some people are at higher risk because of inherited or acquired immune problems, such as Fanconi anemia or immunosuppression after organ transplantation.

Most squamous cell carcinomas of the oral cavity are not caused by human papillomavirus (HPV), unlike cancers of the oropharynx (the area that includes the tonsils and base of the tongue). Because of this, HPV and p16 testing are not routinely performed for oral cavity cancers.

How is the diagnosis made?

The diagnosis is made after a tissue sample is examined under the microscope by a pathologist. The sample is obtained during a biopsy — typically a small incisional biopsy taken from the edge of the abnormal area in the mouth. Under the microscope, the pathologist confirms squamous cell carcinoma when abnormal squamous cells are seen breaking through the epithelium (the surface lining of the mouth) and invading the tissue beneath. The biopsy confirms the diagnosis and provides initial information about grade, but features such as exact depth of invasion, margin status, pattern of invasion, and bone or muscle involvement can only be fully assessed after the entire tumor is surgically removed.

Once cancer is confirmed, imaging studies — usually a contrast-enhanced CT or MRI of the oral cavity and neck — are used to determine the tumor’s extent, whether bone is involved, and whether cancer has spread to nearby lymph nodes. PET-CT may be added for more advanced disease to detect spread elsewhere in the body.

Histologic grade

Histologic grade describes how different the cancer cells look compared to normal squamous cells and how much keratin (a protective protein that squamous cells normally produce) is present in the tumor.

• Well differentiated — The cells closely resemble normal squamous cells and usually form abundant keratin. These tumors tend to grow and spread more slowly.
• Moderately differentiated — The cells show greater variation in size and shape and form less keratin. They are more likely to invade nearby tissue than well-differentiated tumors.
• Poorly differentiated — The cells look very different from normal squamous cells, form little or no keratin, and tend to grow and spread more aggressively.

Histologic grade helps predict how the cancer may behave and contributes to treatment planning, though it is interpreted alongside other features such as depth of invasion and lymph node status.

Depth of invasion

Depth of invasion refers to how far the tumor has grown beneath the normal surface of the mouth, measured in millimeters from the basement membrane (the delicate barrier separating the surface epithelium from the underlying stroma) down to the deepest point of tumor growth.

Depth of invasion is one of the most important measurements in oral cavity squamous cell carcinoma. A greater depth of invasion means the tumor has penetrated further into the tissue, and deeper tumors are significantly more likely to spread to lymph nodes. Depth of invasion is a key determinant of the T category in pathologic staging:

• Depth of invasion of 5 mm or less contributes to a lower T category
• Depth of invasion greater than 5 mm but 10 mm or less raises the T category
• Depth of invasion greater than 10 mm raises the T category further, regardless of tumor surface size

Your pathology report will state the depth of invasion as a specific measurement in millimeters.

Pattern of invasion

Pattern of invasion describes the way cancer cells grow and spread at the leading edge — the advancing front — of the tumor. Pathologists assess this because it provides additional information about how aggressively the tumor behaves, beyond what depth of invasion and grade capture alone.

The most important pattern-based assessment is the worst pattern of invasion (WPOI), which looks at the most aggressive area of the tumor’s advancing edge. The two key patterns are:

• Cohesive invasion (WPOI 1–4) — Cancer cells invade in compact groups or sheets that stay connected to each other. This is generally associated with a lower risk of regional spread.
• Non-cohesive invasion (WPOI-5) — Tumor cells invade as small clusters of five cells or fewer, or as individual cells, widely scattered through the surrounding tissue. WPOI-5 is associated with a significantly higher risk of lymph node spread, local recurrence, and worse overall outcomes. When WPOI-5 is present, it may influence recommendations for elective neck dissection or adjuvant treatment even in otherwise early-stage tumors.

Your report will describe the pattern of invasion as either cohesive or non-cohesive, and may specifically note whether WPOI-5 is present.

Perineural invasion

Perineural invasion means cancer cells are growing along or around a nerve. Nerves run throughout the oral tissues and carry signals for sensation and movement. When tumor cells travel along nerve pathways, there is a greater risk the cancer could return after treatment or spread to nearby areas. Perineural invasion is recognized under the microscope when tumor cells are seen surrounding or tracking within a nerve sheath. Your report will state whether perineural invasion is present or absent.

Lymphovascular invasion

Lymphovascular invasion means cancer cells have entered lymphatic channels or blood vessels near the tumor. When tumor cells are found inside these channels, there is a higher risk that cancer will spread to lymph nodes or distant organs. Your report will state whether lymphovascular invasion is present or absent.

Bone and muscle invasion

Because the oral cavity is closely surrounded by bone (the mandible and maxilla) and muscles used for chewing, swallowing, and speaking, your pathology report may describe whether the tumor has grown into these adjacent structures.

• Bone invasion — The tumor has grown into the cortical bone (outer shell) or cancellous bone (inner spongy layer) of the jaw. The extent and type of bone invasion — superficial erosion versus deep marrow involvement — affects staging and surgical planning. Bone invasion raises the tumor to at least pT4a.
• Muscle invasion — The tumor has grown into adjacent muscles, such as the extrinsic muscles of the tongue (which attach the tongue to the surrounding bones) or the muscles of the floor of the mouth. Involvement of the deep (extrinsic) muscles of the tongue also raises the tumor to at least pT4a.

When bone or muscle invasion is present, surgery typically requires removing the involved bone or muscle as part of a wider resection, and additional treatment with radiation or chemoradiation is commonly recommended.

Surgical margins

Margins are the edges of tissue removed during surgery. After the specimen is received, the pathologist inks the outer surfaces and examines multiple sections under the microscope to determine how close the tumor comes to each edge.

• Negative margin — No cancer cells at the edge. This suggests the tumor was likely removed completely.
• Close margin — Cancer cells are within a few millimeters of the edge but do not reach it. The significance depends on the specific margin site and the treating team’s clinical judgment.
• Positive margin — Cancer cells are present at the cut edge, suggesting some tumor may remain. Further surgery or radiation is usually recommended.

For oral cavity tumors, margins are described separately as mucosal (at the surface lining), deep soft tissue (at the deep aspect of the specimen), and, when bone is removed, bone margins. Each margin is assessed independently because they carry different clinical implications.

Lymph nodes

Lymph nodes are small immune organs located throughout the head and neck region, grouped into levels I through V on each side of the neck. Because squamous cell carcinoma of the oral cavity can spread to these lymph nodes, surgeons often remove them during an operation called a neck dissection. The extent of dissection depends on the location and stage of the tumor.

The pathologist examines each lymph node under the microscope. Your report includes the total number of lymph nodes examined, the number that contain cancer, the size of the largest tumor deposit, and whether extranodal extension is present — meaning cancer has broken through the outer capsule of the node into surrounding tissue. Extranodal extension is a high-risk feature that typically prompts a recommendation for adjuvant chemoradiation.

Lymph node involvement and extranodal extension are among the most important factors for staging and for determining whether additional treatment after surgery is needed.

PD-L1

PD-L1 is a protein that some cancer cells use to shield themselves from immune attack. Immunotherapy drugs called checkpoint inhibitors — particularly pembrolizumab (Keytruda) — work by blocking this mechanism, allowing the immune system to recognize and attack the cancer.

PD-L1 testing is typically performed when the cancer cannot be removed surgically, has come back after treatment, or has spread to other parts of the body. The result is reported as a Combined Positive Score (CPS), which measures the proportion of tumor cells and surrounding immune cells that express PD-L1, expressed as a number from 0 to 100. A CPS of 1 or higher indicates that immunotherapy may provide benefit. A higher CPS is generally associated with a greater likelihood of response. Your oncologist will use the CPS result together with other clinical factors to decide whether immunotherapy is appropriate for your treatment plan.

Pathologic stage (pTNM)

The pathologic stage describes how far the cancer has spread based on examination of the surgical specimen, using the internationally recognized TNM staging system. The T category in oral cavity SCC incorporates both tumor size and depth of invasion — making depth of invasion particularly important for staging. The N category is based on lymph node involvement, including the number and size of deposits and whether extranodal extension is present. The M category (distant metastasis) is determined by imaging rather than pathology.

Tumor stage (pT)

• pT1 — Tumor 20 mm or smaller in greatest dimension AND depth of invasion (DOI) 5 mm or less.
• pT2 — Tumor 20 mm or smaller with DOI greater than 5 mm but not more than 10 mm; OR tumor larger than 20 mm but not more than 40 mm with DOI 10 mm or less.
• pT3 — Tumor larger than 40 mm; OR any tumor with DOI greater than 10 mm.
• pT4a — Tumor invades adjacent structures: through cortical bone of the mandible or maxilla, the maxillary sinus, or the skin of the face; OR tumor involves the deep (extrinsic) muscles of the tongue.
• pT4b — Tumor invades the masticator space, pterygoid plates, skull base, or encases the internal carotid artery. (Very advanced, usually not resectable.)

Nodal stage (pN)

• pN0 — No cancer in any lymph nodes examined.
• pN1 — Cancer in a single lymph node on the same side as the tumor, 30 mm or smaller, with no extranodal extension.
• pN2a — Cancer in a single lymph node on the same side as the tumor, larger than 30 mm but not more than 60 mm, with no extranodal extension.
• pN2b — Cancer in multiple lymph nodes on the same side, all 60 mm or smaller, with no extranodal extension.
• pN2c — Cancer in lymph nodes on both sides of the neck, all 60 mm or smaller, with no extranodal extension.
• pN3a — Cancer in a lymph node larger than 60 mm.
• pN3b — Cancer in any lymph node(s) with extranodal extension present.

What is the prognosis for squamous cell carcinoma of the oral cavity?

The prognosis for oral cavity squamous cell carcinoma depends on several factors, the most important of which are the pathologic stage, depth of invasion, margin status, lymph node involvement, and extranodal extension.

Tumors detected at an early stage — small, superficial, with no lymph node involvement — are often curable with surgery alone, and five-year survival rates for stage I and II oral cavity SCC are generally in the range of 70–90%. As the stage advances — particularly when lymph nodes are involved or extranodal extension is present — survival rates decrease substantially. Stage IV disease with distant metastasis carries a much more guarded prognosis.

Several specific pathologic features are associated with a higher risk of recurrence and worse outcomes:

• Positive or close margins — Significantly increase the risk of local recurrence and typically prompt adjuvant treatment.
• Perineural invasion — Associated with a higher rate of local recurrence and regional spread.
• Extranodal extension — One of the strongest adverse prognostic factors for survival in oral cavity SCC; typically triggers recommendation for concurrent chemoradiation.
• WPOI-5 (non-cohesive invasion) — Associated with significantly higher rates of lymph node metastasis and recurrence, even in early-stage tumors.
• Deep invasion — Depth of invasion greater than 10 mm is associated with substantially higher rates of nodal spread.

Avoiding tobacco and alcohol, maintaining oral hygiene, and attending all scheduled follow-up appointments help reduce the risk of recurrence and a new primary cancer. Recovery of speech, swallowing, and dental function are important long-term goals, and support from speech therapists, dietitians, and dental specialists is often part of the care plan.

What happens after the diagnosis?

After diagnosis, your healthcare team reviews your pathology report, imaging studies, and overall health to develop a personalized treatment plan. The team typically includes a head and neck surgeon, a radiation oncologist, a medical oncologist, and a pathologist.

For most patients, surgery is the primary treatment — removing the tumor with adequate margins and assessing or removing lymph nodes in the neck. If the tumor has high-risk features such as positive or close margins, perineural invasion, extranodal extension, bone or deep muscle invasion, or a high depth of invasion, adjuvant radiation or combined chemoradiation is usually recommended after surgery.

For advanced, recurrent, or metastatic cancer, systemic therapies — including chemotherapy, targeted therapy (cetuximab), or immunotherapy (pembrolizumab or nivolumab for PD-L1-positive tumors) — may be considered.

Questions to ask your doctor

• Where exactly in my mouth did the cancer start, and what is the tumor size?
• What is the depth of invasion, and how does it affect my stage and prognosis?
• Was a worst pattern of invasion (WPOI) reported, and was WPOI-5 present?
• Was perineural invasion or lymphovascular invasion found?
• Did the tumor invade bone or the deep muscles of the tongue or floor of the mouth?
• Were the surgical margins negative? Is additional surgery or radiation needed?
• How many lymph nodes were examined, and did any contain cancer?
• Was extranodal extension present, and does that change my treatment plan?
• What is my pathologic stage (pT and pN)?
• Was PD-L1 testing performed, and what was the CPS score?
• What treatment is recommended after surgery — radiation, chemoradiation, or systemic therapy?
• How will speech, swallowing, and dental health be supported during and after treatment?
• How often will I need follow-up visits and imaging?