Melanocytic tumor of uncertain malignant potential in the hypopharynx

Dear Editor,

While cutaneous melanomas arise from pre‐existing melanocytic nevi, there is no direct evidence demonstrating that oral melanocytic nevi serve as precursor lesions for oral malignant melanoma [1]. Throughout the past several decades, several reports highlighted difficulties in the differential diagnosis between a particular type of melanocytic lesion and true melanoma [2].

A 33‐year‐old man was found to have an increased number of small pigmented papules along with erythematous halo over the trunk, lower extremities, shoulder, upper extremities, and buttocks for the previous 2 years (Figure 1A). Selective skin‐lesion biopsies were performed, and the pathology reported melanocytic nevus with the spitzoid feature. Serum screen and urinalysis were normal. Fiberscope showed two blackish lesions over the left aryepiglottic fold and left pyriform sinus (Figure 1B, arrow). Biopsy was performed through direct laryngoscopy. Microscopic examination of the tissue sections revealed similar histological features of the two nevi, with both showing an atypical Spitz nevus composed of proliferating epithelioid melanocytes with mild atypia at the dermo‐epidermal junction and band‐like inflammation beneath the intradermal component of the nevus. Pagetoid extension of the neval cells within the epidermis was focally discovered. The proliferating epithelioid melanocytes demonstrated mild atypia, and no mitotic figures could be seen [Figures 1C, 1H, and 1E (100×), and Figures 1D, 1H, and 1E (200×)]. Immunohistochemical staining for HMB‐45 showed that the melanocytes were limited to the basal layer of the epidermis, with no pagetoid spread [Figure 1E (100×)]. Computed tomography and magnetic resonance imaging results were negative, and positron emission tomography scan did not report any focal area suggesting a malignant tumor. A diagnosis of melanocytic tumors of uncertain malignant potential was made. The patient received trans‐oral laser microsurgery, with complete excision of his hypopharyngeal tumor without further adjuvant therapy. Following regular follow‐up, the patient remained free of recurrence 6 months after the operation.

Figure 1.

A: small pigmented papules along with erythematous halo were presented over the trunk, lower extremities, shoulder, upper extremities, and buttocks. B: Two blackish lesions over the left aryepiglottic fold and left pyriform sinus were noted under fiberscope (arrow). C&D: The proliferating epithelioid melanocytes demonstrated mild atypia with no mitotic figure. E: The melanocytes were limited to the basal layer of the epidermis with no pagetoid spread under HMB‐45 staining.

The diagnosis and distinction of these lesions from cellular blue nevi and malignant melanomas were often reported as “lack of consensus” [3]. These lesions, including atypical Spitz tumors, atypical blue nevi, and deep penetrating nevi, are often referred to as “melanocytic tumors of uncertain malignant potential” (MELTUMP). To date, the terminology and histological features in this field remain unstandardized; however, most doctors would agree that these lesions should be categorized as low‐grade tumors with potential for lymph‐node metastasis and, rarely, distant metastasis.

Berk et al [4] reported a relatively high rate of MELTUMPs with regional nodal disease and emphasized the need for close follow‐up. It appears that lymph node involvement in MELTUMPs occurs frequently, but perhaps due to its low malignant potential, the incidence of subsequent deadly disease remains low [5]. The term MELTUMP is derived from the diagnostic difficulty in classifying these lesions as benign or malignant. These lesions in oral mucosa are exceedingly rare, but the diagnosis may be taken into consideration when encountering pigmented mucosal lesions.