ABSTRACT: We report the case of a 74-year-old man with metastatic melanoma of the small bowel. Melanoma metastasizing to the small bowel is a rare but well described presentation of the disease, detected clinically in only 2% to 5% of these patients. Its presentation is similar to other gastrointestinal tract tumors, with symptoms of abdominal pain or anemia prevailing. Recent studies have implicated the chemokine receptor CCR9 and its ligand CCL25 as signals that allow malignant melanoma cells to preferentially metastasize to the small bowel. Common imaging modalities used to detect these small bowel lesions include contrast-enhanced computed tomography (CT) scans and upper gastrointestinal series with small bowel follow-through. Given the low sensitivity of these modalities, newer helical CT scanners, 18F-2-fluoro-2-deoxy-D-glucose–positron emission tomography (FDG PET)/CT, and capsule endoscopy are now being recommended to replace the older imaging techniques. Current treatment modalities include surgical resection, which has been shown to increase overall survival, and adjuvant immunotherapy, whose efficacy is currently being questioned. A review of the current literature describing this rare occurrence is included to compare with our patient's presentation, diagnosis, and management.
Melanoma frequently metastasizes to the small bowel. In this installment of Clinical Quandaries, we describe the case of 74-year-old man who presented with this rare but well described manifestation of malignant melanoma.
Case Report
Capsule Endoscopy
A 74-year-old man with a 3-year history of malignant melanoma presented with an episode of lower gastrointestinal (GI) bleeding. He developed progressively worsening anemia and required frequent transfusions (totaling 2 units of packed red blood cells). During an extensive GI workup, he was noted on capsule endoscopy to have one ulcerated and bleeding lesion in the ileum that was not accessible to endoscopic biopsy (Figure 1). 18F-2-fluoro-2-deoxy-D-glucose–positron emission tomography (FDG-PET) imaging revealed increased uptake around the left fourth rib as well as a focus of activity in both the right and left lower quadrant of the bowel (Figure 2).
In addition to anemia, the patient described symptoms of anorexia, a 30 lb weight loss over the past 6 months, and weekly episodes of melena. His past medical history includes surgical resection of two separate cutaneous lesions on his back followed by 6 months of interferon-alpha therapy which was stopped due to poor patient tolerance. In the past year, he was noted to have bilateral axillary lymphadenopathy on exam. This was thought to represent metastatic disease, for which he underwent bilateral axillary lymph node dissections. Only one lymph node in each axilla was found to be positive for malignancy, and the patient received no further treatment at that time.
FDG-PET
After consultation and review of the current PET imaging, the patient underwent surgical resection of the area of increased uptake in the small bowel with its attached mesentery and lymph nodes. Two abnormal lesions were found in the ileum. The smaller lesion was proximal and appeared to be an intussusception, and the other more distal lesion was a 3- to 4-cm intraluminal mass, nearly circumferential in nature (Figure 3). The distal lesion was approximately 60 cm from the cecum, and the proximal lesion, about 90 cm. No other intra-abdominal metastases were found.
Pathologic review of the resected lesions included immunohistochemical staining with a melanoma cocktail (Figure 4). The distal lesion was diagnosed as a metastatic melanoma with both proximal and distal margins free of tumor involvement (although the serosal margin was less than 1 mm from the tumor) and four out of four lymph nodes showing no evidence of malignancy. Postoperatively, the patient is doing well without major complications and is being evaluated for further adjuvant therapy.
Discussion
Gross Resection
the small bowel. A large review of autopsies in 1964 at Memorial Sloan-Kettering Cancer Center found that the small bowel was the most common site of metastasis, found in 58% of malignant melanoma patients.[1] Another study, in 1999, also demonstrated that a large proportion of patients (50%) had metastasis to the small bowel.[2] These findings have been confirmed in other autopsy studes.[3] Though it is prevalent, small bowel metastasis has been detected clinically in only 2% to 5% of patients with malignant melanoma.[4] The average time of detection of metastasis after diagnosis of the primary tumor, for all GI tract metastasis, was 43.8 ± 11.3 months.[5] A study by Bender et al in 2001 showed similar results, with the average time from diagnosis to detection at 3.2 years.[6] The most typical symptoms at presentation were anemia or abdominal pains, but can include fatigue, constipation, tenesmus, small bowel obstruction, perforation, intussusception, and hematemesis.[3]
In addition, cases of primary melanoma of the small bowel have been reported. These are not only rare, but often are difficult to distinguish from a primary lesion.[3,7] Suggested clinical criteria for differentiation of primary from metastatic small bowel involvement include lack of concurrent or previous removal of a melanotic lesion, no other organ involvement, in situ change in adjacent GI epithelium, and disease-free survival of 12 months after initial diagnosis.[8] Histologic criteria for primary melanoma of the small bowel include observation of one or more of the following: varying proportions of spindle cells, junctional proliferation within the mucosa, large eosinophilic nuclei, and excess cytoplasm.[7,9] Ultimately, the prognosis for these patients is poor, with a median survival of only 4 to 6 months.[3]
