Clinicopathologic Observations on Primary Malignant Melanoma of the Digestive Tract

Objective We aimed to investigate the clinical features, histopathological characteristics, immunohistochemical profile, diagnostic and differential diagnostic approaches, and treatment strategies for primary malignant melanoma of the digestive tract. Methods A retrospective analysis was conducted on 21 patients diagnosed with primary malignant melanoma of the digestive tract between January 2011 and July 2024. The clinical, morphological, and immunohistochemical features of these tumors were systematically evaluated. Results The study cohort included 21 patients (age range: 42-90 years; mean age: 64.8 years) diagnosed with primary malignant melanoma of the digestive tract. All patients underwent surgical treatment, with the majority of tumors located in the anorectal region (15/21), followed by the small intestine (4/21) and esophagus (2/21). Histopathological examination revealed nodular proliferation patterns under low magnification. The tumors were predominantly composed of sheets of epithelioid or spindle-shaped cells that exhibited marked pleomorphism. Melanin pigmentation was identified in 11 tumors. High-power microscopic evaluation demonstrated significant cellular polymorphism, with round, vesicular nuclei containing prominent eosinophilic nucleoli. Frequent mitotic figures were observed throughout the specimens. Notably, two tumors exhibited signet-ring cell-like morphology, characterized by cytoplasmic clearing and peripheral nuclear displacement. Analysis of tumor invasion depth revealed that seven tumors infiltrated the submucosa, six tumors infiltrated the muscularis propria, and eight tumors infiltrated the entire wall. Lymph node metastasis was detected in five patients. Conclusion Primary malignant melanoma of the digestive tract represents a rare malignancy requiring high clinical suspicion. Endoscopic identification of pigmented lesions should prompt consideration of this diagnosis. Definitive diagnosis requires histopathological confirmation through H&E staining supplemented by immunohistochemical markers (eg, S-100, HMB45, melan-A), combined with imaging tests to exclude metastatic lesions from cutaneous or ocular primary sites.