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Introduction: Malignant peritoneal mesothelioma (MPM) is a rare cancer that is associated with asbestos exposure. The diagnosis can be difficult given the nonspecific nature of presenting symptoms and the presence of concomitant confounding findings. Case Presentation: We report a 71-year-old male who presented with right lower quadrant pain and new-onset ascites. CT imaging of the abdomen/pelvis demonstrated omental stranding concerning for a possible omental infarction. Subsequent imaging showed persistent omental edema but no identifiable soft tissue mass. A biopsy of the omentum showed atypical mesothelial proliferation, but pathology was unable to determine if proliferation was a neoplastic versus reactive process. Surgical oncology performed a diagnostic laparoscopy that showed peritoneal studding of the omentum. Subsequent immunohistochemical staining of the omentum demonstrated preservation of BAP1 expression and loss of MTAP expression, consistent with peritoneal mesothelioma. Conclusion: MPM is a rare and aggressive cancer with an overall poor prognosis. The diagnosis of MPM can be difficult based on the nonspecific clinical presentation, insufficient imaging and laboratory testing, and the presence of concomitant confounding findings, such as with this patient and his admitting diagnosis of omental infarction. This case demonstrates the importance of developing a broad differential while maintaining an awareness of heuristics that can influence clinical decision-making.
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Background: Rosai Dorfman disease is a rare non-Langerhans cell histiocytosis that affects lymph nodes, soft tissues, and other organs. The etiology of Rosai Dorfman disease is poorly understood, though it may involve an immunologic processes or infection. Treatment varies according to the disease presentation. Case Presentation: A male aged 56 years was evaluated for a cutaneous mass on his right medial thigh. Initially, the patient received surgical debulking with subsequent observation and no systemic therapy. However, the mass recurred, prompting another surgical removal 9 years after the initial surgery. A mass biopsy showed infiltration of plasma cells, lymphocytes, histiocytes, and occasional neutrophils with noted reactivity of S-100 protein and CD163, but not CD1a. No systemic therapy was initiated, and the patient agreed to a period of watchful waiting. Conclusions: Rosai Dorfman disease of soft tissue occurs in older adults and is often associated with soft tissue abnormalities, and more rarely, in lipomas. Multidisciplinary management of the disease and research for mutations and microenvironment of RDD is needed to better understand its clinicopathological nature and improve novel therapies.