Diagnosis of an Extensive Primary Gingival Melanoma by Immuno-histochemical Marker Analysis with Human Melanoma Black 45 (HMB45) and Soluble Calcium Binding Proteins (S100): A Rare Case Report with Literature Review

Background: Primary gingival melanoma is an uncommon oral malignancy that can mimic other pigmented lesions and present a diagnostic challenge. This report describes the clinical and histopathological features of an extensive maxillary gingival lesion and the contribution of HMB45 and S100 immunohistochemical assessment. Case Presentation: A 56-year-old man reported swelling of the right maxillary gingiva for eight months, with progression during the preceding months. Examination revealed a diffuse, tender gingival enlargement extending buccally and palatal from teeth 11 to 16. The lesion measured approximately 6 × 1.5 cm, with black pigmentation in its anterior third. Grade III tooth mobility, generalised periodontal bone loss and right submandibular lymphadenopathy were also recorded. Following extraction of the mobile teeth, the lesion was surgically excised. Histopathological examination demonstrated atypical melanocytes involving the basal epithelial layer and invading the underlying connective tissue, with scattered melanin pigment. Immunohistochemical examination using HMB45 and S100 contributed to the diagnosis of malignant gingival melanoma. The patient was referred for oncological management. Early postoperative healing was uneventful, and no local recurrence was identified at the three-month follow-up. Subsequently, the patient received two rounds of chemotherapy without a satisfactory response and ultimately died. Conclusion: This case illustrates the importance of recognizing persistent pigmented gingival enlargement, obtaining histopathological confirmation and interpreting immunohistochemical findings within the clinical context.