Mucosal Melanoma of the Oral Cavity: Understanding Your Pathology Report

by Jason Wasserman MD PhD FRCPC
February 25, 2026

Mucosal melanoma of the oral cavity is a rare and aggressive cancer that arises from melanocytes, the cells that produce pigment (melanin).

Melanocytes are normally present in small numbers within the surface lining of the mouth, called the epithelium. When these cells grow uncontrollably and form a malignant tumor, the condition is called mucosal melanoma.

Unlike cutaneous melanoma, mucosal melanoma develops on internal surfaces and is not associated with sun exposure. In the oral cavity, it most commonly arises on the upper gums (maxillary gingiva) and the hard palate, although it can occur anywhere in the mouth.

How common is mucosal melanoma?

Mucosal melanoma of the head and neck is rare. It accounts for less than 1% of all melanomas and a very small percentage of oral cancers. It most often affects older adults and is uncommon in younger individuals.

What causes mucosal melanoma?

The exact cause is not fully understood. Unlike cutaneous melanoma, mucosal melanoma is not linked to ultraviolet light exposure.

Some tumors may arise in areas of long-standing mucosal pigmentation, called mucosal melanosis, but many develop without a known precursor. There is no proven link to tobacco, alcohol, or environmental carcinogens.

Mucosal melanoma differs biologically from cutaneous melanoma and has a distinct pattern of genetic changes.

What symptoms can occur?

Oral mucosal melanoma may be painless in early stages and is sometimes discovered during a routine dental examination.

It often appears as a dark brown, black, or irregularly pigmented patch, plaque, or nodule. Some tumors may lack visible pigment (amelanotic melanoma), making them appear pink or flesh-colored. Ulceration, bleeding, swelling, or loosening of teeth may occur. Enlarged lymph nodes may be present at diagnosis.

How is this diagnosis made?

The diagnostic process begins with a biopsy of a suspicious lesion. The tissue is examined under the microscope by a pathologist.

The diagnosis is confirmed when highly atypical malignant cells show evidence of melanocytic differentiation, meaning they produce melanin pigment or express melanocyte-related proteins.

Microscopic features

Under the microscope, mucosal melanoma is composed of markedly abnormal cells that may vary in shape and appearance. Tumor cells may be epithelioid (large and polygonal), spindle-shaped, round, plasmacytoid, or undifferentiated. Multiple cell types are often seen in the same tumor.

The tumor may grow in sheets, nests, or intersecting bundles. Invasive growth into the underlying connective tissue is common, and in advanced cases, invasion into bone may occur.

The surface epithelium may show abnormal melanocytes spreading upward (called pagetoid spread) or lining the basal layer in a linear pattern (called lentiginous growth).

Mitotic figures are often numerous and may appear abnormal. Necrosis, lymphovascular invasion, and perineural invasion are common.

Immunohistochemistry

Immunohistochemistry is a laboratory test that uses antibodies to detect specific proteins inside tumor cells. This test is especially important when the tumor lacks visible pigment or when the diagnosis is uncertain.

In mucosal melanoma, tumor cells typically express melanocytic markers such as:

• S100

• SOX10

• HMB45

• Melan-A (MART1)

• Tyrosinase

• MITF

No single marker is completely reliable, so pathologists use a panel of markers. Expression may be strong in epithelioid tumors and weaker or patchy in spindle cell tumors.

Immunohistochemistry helps distinguish mucosal melanoma from other cancers that can appear similar, including poorly differentiated squamous cell carcinoma, neuroendocrine carcinoma, lymphoma, and sarcoma.

Subtypes of mucosal melanoma

A subtype is a specific form of a cancer that shares the main features of the overall disease but has distinct microscopic characteristics. Identifying a subtype can provide additional information about tumor behavior and may influence treatment decisions.

Mucosal lentiginous melanoma

This subtype shows abnormal melanocytes spreading linearly along the basal layer of the epithelium. This growth pattern is common in oral mucosal melanoma.

Nodular melanoma

This subtype grows as a more compact, nodular mass and may show a minimal surface component (in situ). It is often deeply invasive at the time of diagnosis.

Desmoplastic mucosal melanoma

This rare subtype is composed mainly of spindle-shaped tumor cells embedded in dense fibrous tissue. It may lack visible pigment and can resemble other spindle cell tumors. Perineural invasion is frequently present. Diagnosis often requires extensive immunohistochemical testing.

Depth of invasion

Depth of invasion describes how far the tumor has grown into surrounding tissues. In many cancers, this measurement is a major factor in staging and prognosis.

Depth of invasion is assessed by examining the tumor under the microscope and determining how deeply it extends beneath the surface epithelium. It may also be evaluated using imaging studies.

However, in mucosal melanoma of the head and neck, depth of invasion is less useful for staging than in skin melanoma. Unlike skin melanoma, where thickness (Breslow depth) is critical, mucosal melanoma is staged differently. In current staging systems, most mucosal melanomas are considered advanced (T3 or T4) at diagnosis due to their aggressive behavior.

Although depth is documented, the overall stage is more strongly influenced by local extension and spread to lymph nodes or distant organs.

Lymph nodes and nodal stage

Lymph nodes are small immune organs that help filter harmful substances. Cancer cells can spread to lymph nodes through lymphatic vessels.

During surgery or staging evaluation, lymph nodes may be removed and examined under the microscope. Your pathology report will describe lymph nodes as:

• Positive, if cancer cells are found.

• Negative, if no cancer cells are found.

The number of positive lymph nodes is used to determine the nodal stage. Lymph node involvement is associated with a higher risk of distant spread and a poorer prognosis.

In some cases, enlarged lymph nodes are identified through imaging or biopsy at the time of diagnosis.

Perineural invasion

Perineural invasion (PNI) means cancer cells are seen growing along or around a nerve. Nerves carry signals between the brain and other parts of the body.

Perineural invasion is common in mucosal melanoma and is considered a high-risk feature because it indicates aggressive local spread.

Biomarkers

Biomarkers are proteins or genetic changes found in tumor cells that may help guide treatment decisions. In mucosal melanoma of the oral cavity, biomarker testing is most often performed in advanced or metastatic disease to identify potential targeted therapy or immunotherapy options.

KIT

KIT is a gene that produces a protein involved in regulating cell growth and survival. Mutations in the KIT gene are more common in mucosal melanoma than in melanoma of the skin. When KIT is altered, it can send continuous growth signals to tumor cells, allowing them to multiply uncontrollably. Identifying a KIT mutation is important because some patients may benefit from targeted therapies that block the abnormal KIT protein.

Testing for KIT mutations is performed using molecular genetic techniques on tumor tissue. Results are reported as either a detectable KIT mutation or no mutation identified. If a mutation is present, the specific type of mutation may be described in the report.

BRAF

BRAF is a gene that plays a role in controlling cell growth through the MAPK signaling pathway. BRAF mutations are common in melanoma of the skin but are less common in mucosal melanoma. When present, a BRAF mutation can cause uncontrolled tumor growth. Identifying this mutation is important because patients with certain BRAF mutations may benefit from targeted therapy that blocks the abnormal signaling pathway.

BRAF mutations are detected using molecular testing performed on tumor tissue. The report will indicate whether a BRAF mutation is present. If present, the specific mutation type may be listed.

PD-L1

PD-L1 is a protein that helps tumor cells evade immune detection. When PD-L1 binds its receptor on immune cells, it signals to reduce the immune response. Some mucosal melanomas express PD-L1, which may make them more responsive to immune checkpoint inhibitors, a type of immunotherapy that helps the immune system attack cancer cells.

PD-L1 is tested using immunohistochemistry on a tissue sample from the tumor. Results are typically reported as the percentage of tumor cells showing PD-L1 staining or using a scoring system, depending on institutional practice. Higher levels of expression may increase the likelihood of response to immunotherapy, although treatment decisions depend on multiple clinical factors.

Prognosis

Mucosal melanoma of the oral cavity is an aggressive cancer. The 5-year overall survival rate ranges from approximately 20% to 50%.

Prognosis depends on tumor size, local extension, lymph node involvement, and distant metastasis. Early detection and complete surgical removal offer the best chance for long-term survival.

Questions to ask your doctor

• Has the tumor spread to lymph nodes or distant organs?

• Was complete surgical removal possible?

• Were high-risk features such as perineural invasion present?

• Were biomarker tests performed?

• Are targeted therapy or immunotherapy options available?

• What stage is my cancer, and what does that mean for my treatment plan?