Which histologic findings are characteristic of oral malignant melanoma?

Updated: Jan 31, 2020
  • Author: Elizabeth Ann Bilodeau, DMD, MD, MSEd; Chief Editor: Jeff Burgess, DDS, MSD  more...
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Answer

Although any of the features of cutaneous malignancy can be found, most oral melanomas have characteristics of the acral lentiginous (mucosal lentiginous) and, occasionally, superficial spreading types.

The presence of pigmentation brings the possible diagnosis of melanoma to the fore, but iron stains and melanin bleaching may be necessary to characterize the pigmentation. An absence of pigmentation requires greater emphasis on recognition of cytomorphologic and architectural characteristics of melanoma, as well as recognition of lymphocytes in the inflammatory reaction in an amelanotic melanoma.

Oral melanoma composed predominately of spindle ce Oral melanoma composed predominately of spindle cells. Melanin is not seen within the field; additional immunohistochemical stains are required to confirm a diagnosis (hematoxylin and eosin, original magnification 20x).

The malignant cells often nest or cluster in groups in an organoid fashion; however, single cells predominate at the junction in portions of the epithelium (see the images below). There is little evidence of maturation or dispersion at the base of the tumor.

Histologic image of a polypoid mass. Rounded colle Histologic image of a polypoid mass. Rounded collections or nests of melanocytes fill the connective tissue and have tropism for the surface epithelium (hematoxylin and eosin, original magnification, ×2). This mass was excised from the lingual surface of the posterior mandible of an elderly man. The diagnosis is oral melanoma.
Tumor cells show affinity for the surface epitheli Tumor cells show affinity for the surface epithelium (merging of tumor and epithelium). In this image, cellular pleomorphism and smudged nuclei with pseudoinclusions are noted (hematoxylin and eosin, original magnification, ×10). The diagnosis is oral melanoma.

The melanoma cells have large nuclei, often with prominent eosinophilic nucleoli, and show nuclear pseudoinclusions due to nuclear membrane irregularity (see the following image). The abundant cytoplasm may be uniformly eosinophilic or optically clear. Fine and coarse intracytoplasmic pigment may be evident. Occasionally, the cells become spindled (sarcomatoid) or neurotize in areas. In the oral mucosa, the prognosis is dismal for patients with any architectural type (spindled, pleomorphic, plasmacytoid, undifferentiated) of cell. Metastatic spread to the cervical and supraclavicular lymph nodes is a common finding.

This image shows rounded nest of various sized mel This image shows rounded nest of various sized melanocytes with nuclear pseudoinclusions (hematoxylin and eosin, original magnification, ×40). The diagnosis is oral melanoma.

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