A Case of Amelanotic Malignant Melanoma of the Lingual Base That Was Diagnosed Based on a Biopsy of Late Metastasis to a Lumbar Vertebra after Being Misdiagnosed as HPV-Positive Oropharyngeal Anterior Wall Squamous Cell Carcinoma

Figure 5

The microscopic findings of the resected L4 bone marrow (A) and pharyngeal tumor (a) are shown. HE staining did not reveal melanotic granules in the malignant cells of either lesion. Proliferating atypical cuboidal cells with hyperchromatic nuclei and nucleoli were distributed in small nests or as single cells and had invaded the stroma. No apparent intercellular bridges or keratinization was observed. Immunohistochemically, the L4 bone marrow tumor cells were diffusely positive for p16 (B). They also produced positive results during HMB-45 (D) and melan-A (F) staining, but negative results during AE1/AE3 (c) and S-100 (e) staining. Similarly, the pharyngeal tumor cells were diffusely positive for p16 (b). They also produced partially positive results during HMB-45 (d), S-100 (e), and melan-A (f) staining and negative results during AE1/AE3 (c) staining.