Fibrin-Associated Diffuse Large B-Cell Lymphoma Occurring as a Pararenal Pseudocyst

Abstract

Abstract A 60-year-old male underwent nephrectomy for a tumor on the posterior aspect of the right kidney. Grossly, a completely encapsulated 8 × 8 × 6.8-cm nodule was found in the perinephric fat adjacent to the renal capsule and indenting the renal surface. The renal parenchyma was microscopically unremarkable. The capsule of the lesion was composed of dense fibrous tissue with chronic inflammation, remote hemorrhage, and prominent calcifications. The nodule/pseudocyst contained predominantly amorphous, eosinophilic material with cholesterol clefts and calcifications. Within the pseudocyst, clusters of large cells were identified. These cells showed abundant amphophilic cytoplasm and large pleomorphic nuclei with dispersed chromatin, prominent nucleoli, and occasional mitotic figures. Immunohistochemical (IHC) staining showed that these cells were positive for CD20, CD79a, IRF4, BCL2 (>90%), C-MYC (70-80%), and EBV-ISH; variably positive for CD30 and PAX5; and negative for CD3, CD10, CD68, CD138, ALK1, and BCL6. MYC FISH break-apart probe demonstrated no rearrangements or copy number changes. Based on the overall features, the diagnosis of fibrin-associated diffuse large B-cell lymphoma (FA-DLBCL) was rendered. This entity has been recently recognized under a larger category of diffuse large B-cell lymphoma associated with chronic inflammation (DLBCL-CI). Unlike DLBCL-CI, which is considered clinically aggressive, FA-DLBCL typically demonstrates a favorable outcome with surgical resection alone. FA-DLBCL is usually incidentally found at unusual sites (cardiac myxomas, prosthetic cardiac valves, thrombi, hematomas, and pseudocysts including intracranial, splenic, retroperitoneal, paratesticular, adrenal, and renal). To our knowledge, this is the first report of a FA-DLBCL arising in a pararenal location. In addition, our case demonstrates unusually high MYC IHC positivity. Although rare, this entity should be kept in mind, especially in an appropriate clinical setting, and should not be misclassified into a more aggressive category, such as “double expressor” DLBCL or DLBCL-CI.