Jejunal Metastasis from Malignant Pleural Mesothelioma during Long-Term Nivolumab Therapy: A Case Report and Literature Review

INTRODUCTION: Gastrointestinal metastasis from malignant pleural mesothelioma (MPM) is exceedingly rare and lacks a standardized diagnostic work-up. CASE PRESENTATION: An 87-year-old man with asbestos exposure and a 5-year history of left-sided MPM, radiographically stable on long-term nivolumab therapy, presented with melena and anemia. Contrast-enhanced CT revealed a circumferential jejunal lesion near the duodenojejunal flexure with enlarged mesenteric nodes. Double-balloon enteroscopy confirmed a 40-mm obstructive tumor, but biopsies were non-diagnostic. Partial jejunectomy with targeted mesenteric lymph-node dissection was performed. Histology with a mesothelioma-oriented immunohistochemical panel-negative for CEA and BerEP4 and positive for broad-spectrum cytokeratins-supported a diagnosis of metastatic MPM; nodal metastases were present. Given his age, no further systemic therapy was administered; the patient died 20 months postoperatively from progression of MPM. CONCLUSIONS: In MPM receiving immune-checkpoint inhibitor therapy, unexplained gastrointestinal bleeding should prompt comprehensive gastrointestinal evaluation, including small-bowel assessment. Surgery can secure symptom relief and a definitive diagnosis.