Oral lichenoid lesion（OLL）is defined as a clinical and histopathological entity resembling oral lichen planus（OLP）, yet its conceptual boundaries remain ambiguous, leading to diagnostic and classificatory confusion. This paper demonstrates the history of OLL, its current global recognition, and its recognition in Japan from both clinical and pathological perspectives, acknowledging this ambiguity. Additionally, the paper reviews OLP-mimicking lesions, including mucous membrane pemphigoid, systemic/discoid lupus erythematosus, and chronic ulcerative stomatitis, discussing their diagnostic challenges and overlaps or relations with OLL.

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A spindle cell lipoma（SCL）is a rare benign lipomatous tumor that has been defined by Enzinger as a new lipomatous entity. The patient was a 70-year-old woman who complained of swelling of the left tongue. The mass was surgically removed with the patient under general anesthesia, and the histopathologyical diagnosis was spindle cell lipoma. There was no sign of recurrence 12months after operation. We reviewed reports documenting 14 cases of oral SCL in Japan. The age of onset was 42-78 years old. There were 8 males and 6 females.

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Erythema multiforme is an inflammatory disorder affecting the skin and mucous membranes, often triggered by infections and medications. We report the case of an 18-year-old female with a history of reactivation herpes simplex virus infections. She presented with lesions on the skin, ocular mucosa, and labial and oral mucosa. Systemic corticosteroid therapy led to marked clinical improvement. Based on histopathological findings and the clinical course, the patient was diagnosed with erythema multiforme major associated with herpes simplex reactivation. Early differentiation and interdisciplinary collaboration were critical for prompt therapeutic intervention.

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Malignant pleural mesothelioma is an aggressive tumor arising from pleural mesothelial cells, and oral metastasis is extremely rare. An 83-year-old man presented with a right mandibular gingival tumor, diagnosed as metastasis of epithelioid malignant pleural mesothelioma. Combined nivolumab and ipilimumab therapy resulted in near-complete disappearance of the oral lesion within one month and marked response of the primary tumor. No recurrence has been observed during 18 months of follow-up. To our knowledge, no previous report has described such a favorable response in the case of oral metastasis of malignant pleural mesothelioma in Japan.

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