A case of squamous cell carcinoma of the lower gingiva accompanied by oral melanosis

We report a rare case of squamous cell carcinoma of the lower gingiva with extensive melanosis. The patient was a 74-year-old woman who presented with a black lesion on the oral mucosa of the lower lip. A mildly protruding lesion was recognized on the left side of the lower lip, left buccal mucosa, and floor of the mouth. The lesion measured about 4.0 × 0.8cm. There was no associated ulcer or induration: A leukoplakia-like white lesion was found on the lower gingiva around the anterior teeth. The white lesion measured about 2.0 × 0.5cm. Although melanin pigmentation increased after the first visit, there was scant evidence of malignant melanoma. A definite clinical diagnosis therefore could not be made. The lesions were excised totally by surgery. Histopathological examination showed continuous changes from the black lesion to well differentiated squamous cell carcinoma with severe epithelial dysplasia. This is a rare case of hyperkeratosis that resembled pseudohorn cyst. The prognosis of this patient remains good 10 months after operation, without recurrence or metastasis.