Primary oral malignant melanoma of the tongue

A 30-year-old man presented with a two-month history of tongue discolouration. Past medical history was negative for skin disorders. Physical examination of the oral cavity revealed general poor dentition with suspicious tar staining of teeth from cigarette smoking/tobacco use. Further examination showed numerous, flat to slightly raised, ill-defined, non-tender and purple lesions involving the dorsum of the tongue with scattered islands of leucoplakia (Figure 1A). Patient had no other lesions within the oral cavity. Biopsy of the lesions showed malignant melanoma. Full oncological work-up showed no evidence of regional or distant metastasis. Patient was managed with subtotal glossectomy, bilateral supraomohyoid neck dissections and reconstruction with a revascularised radial forearm free flap. Histopathological examination showed sheets of epithelioid and spindle-shaped malignant melanocytes (Figure 1B). Immunohistochemical examination showed positive reactivity to S-100 and HMB-45 proteins. The bilateral supraomohyoid neck dissections were negative for malignancy. The final histopathological diagnosis was compatible with primary oral malignant melanoma (OMM) of the tongue. Post-operatively, no adjuvant therapy was administered, and the patient had an uneventful recovery course. No recurrence was detected at 12-month follow-up.

Figure 1A: Primary oral malignant melanoma (OMM) of the tongue.

Gross picture of the tongue showing multiple, flat to slightly elevated, non-tender, ill-defined and whitish-purple lesions with scattered islands of leucoplakia.

Figure 1B: Primary oral malignant melanoma (OMM) of the tongue.

Histopathological examination of the subtotal glossectomy showing sheets of epithelioid and spindle-shaped malignant melanocytes (H&E stain, magnification power: 40x).

Primary OMM of the tongue is rare, and can originate from pre-existing melanocytic (pigmented) lesions, or develop de novo from a malignant transformation and an uncontrolled proliferation of neural crest-derived melanocytes that are normally situated in the basal layer of oral mucosa.1 Australia and New Zealand harbour the highest incidence rates of cutaneous malignant melanoma worldwide.2 However, to the best of knowledge, from New Zealand, no single case of primary non-cutaneous (mucosal) OMM has been reported in the PubMed literature.

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