Colonic malignant melanoma, primary or metastatic? Case report

Area of Science:

• Gastroenterology
• Oncology
• Pathology

Background:

• Malignant melanomas in the gastrointestinal tract are rare, with ongoing debate about primary origins outside the esophagus and anorectum.
• Primary gastrointestinal melanoma is exceptionally uncommon, particularly in the cecum.

Observation:

• A 30-year-old male presented with abdominal pain and diarrhea due to a large cecal tumor.
• Histological examination revealed pleomorphic tumor cells positive for S-100 protein, HMB-45, Melan-A, and vimentin, despite lacking apparent pigment.

Findings:

• The cecal tumor, measuring 14x11x4.5 cm, was primarily submucosal.
• Immunohistochemical analysis supported melanoma, with no evidence of cutaneous or ocular primary melanoma, despite a history of nevus excision.
• Postoperative follow-up showed no recurrence or metastasis one year later, suggesting a primary cecal origin.

Implications:

• This case underscores the diagnostic difficulties in distinguishing primary gastrointestinal melanoma from metastatic disease.
• It emphasizes the importance of thorough investigation and immunohistochemistry in diagnosing rare GI tumors.
• The findings contribute to the literature on rare gastrointestinal malignancies and their origins.