Melanoma of unknown primary presenting as intestinal obstruction: a diagnostic challenge

BACKGROUND: Metastatic melanoma concerning the gastrointestinal (GI) tract is a well-documented yet often clinically silent phenomenon, with the most common site of involvement being the small intestine. Intussusception in adults is rare and usually secondary to an underlying tumor. Melanoma of unknown primary (MUP), a diagnosis made in the absence of identifiable cutaneous, mucosal, or ocular lesions, adds further diagnostic complexity. CASE PRESENTATION: We present the case of a 64-year-old female who was referred to the Emergency Department with subacute symptoms of intestinal obstruction. Imaging revealed ileal intussusception with a suspected tumoral cause. Surgical exploration confirmed an ulcerated intraluminal mass acting as the lead point. A segmental enterectomy with primary anastomosis was accomplished. Histopathological (HP) and immunohistochemical results confirmed the diagnosis of malignant melanoma, with positive staining for S100, Melan-A, preferentially expressed antigen in melanoma (PRAME), and cluster of differentiation 117 (CD117). No primary lesion was identified on full-body dermatological and mucosal examination. The patient had a favorable postoperative outcome and was discharged with a favorable clinical status. DISCUSSIONS: This particular case illustrates an uncommon initial manifestation of metastatic melanoma in the form of small bowel occlusion. MUP remains an infrequent disease with a paradoxically similar or even more favorable prognosis compared to melanomas with known primaries. Literature review supports surgical resection as the primary therapeutic strategy in isolated GI metastasis, particularly in symptomatic patients. Immunohistochemistry plays a critical role in establishing diagnosis, although it cannot reliably distinguish primary from metastatic lesions in the small bowel. CONCLUSIONS: Melanoma should be taken into consideration in the differential diagnosis of adult intussusception and small bowel tumors, even without a known primary lesion. This particular case highlights the importance of HP evaluation and multidisciplinary assessment in reaching an accurate diagnosis.