Microscopic diffuse large B-cell lymphoma (DLBCL) occurring in pseudocysts: do these tumors belong to the category of DLBCL associated with chronic inflammation?

We report 2 cases of localized, microscopic diffuse large B-cell lymphoma (DLBCL) that were detected incidentally within pseudocysts. In case 1, the neoplasm was identified within a 26-cm, 860-g adrenal gland pseudocyst. In case 2, the neoplasm was detected within a 9-cm, 90-g paratesticular pseudocyst. In both cases, the neoplastic cells were large, had a nongerminal center B-cell immunophenotype, and were positive for Epstein-Barr virus (EBV)-encoded RNA detected by in situ hybridization. The most appropriate classification of these tumors using current World Health Organization classification is uncertain. The best fit seems to be DLBCL associated with chronic inflammation (DLBCL-CI), defined as DLBCL arising in the context of long-standing chronic inflammation and associated with EBV infection, with the prototype for this category being pyothorax-associated lymphoma. This term has been used by others in the literature for tumors similar to the cases reported here. However, in the 2 cases we report chronic inflammation was not a prominent feature, and the inflammatory cells that were present showed little relationship to the lymphoma cells. The findings in these cases have led us to question the role of chronic inflammation in pathogenesis. Perhaps the closed space of the pseudocyst, by preventing a cytolytic response to EBV-infected cells, results in local immunodeficiency that may be most important for pathogenesis. We also have concerns about using the term DLBCL-CI for these tumors. Perhaps the cases we report and the few other similar cases reported previously deserve their own category in a future version of the World Health Organization classification.