Case Report: Clonal evolution of diffuse large B-cell lymphoma to plasmablastic lymphoma: diagnostic challenges in a case of gastric lesion with EBV-negative PBL.

[BACKGROUND] The clonal evolution from a diffuse large B-cell lymphoma (DLBCL) to a plasmablastic lymphoma (PBL) is uncommon, presenting remarkable clinical challenges. This phenomenon has critical diagnostic and therapeutic implications, particularly in cases of EBV-negative lesions that show immunophenotypic divergence.

[CASE SUMMARY] We herein report an unusual case of two different immunophenotypes, namely DLBCL in the porta hepatis and concomitant PBL in the stomach. Immunoglobulin gene rearrangement analysis confirmed that the two tumors had the same clonal origin. The patient presented with characteristic PBL features, including loss of CD20 expression, high MYC expression, co-expression of BCL2, and a distinctive clinical manifestation involving gastric mucosa. The patient demonstrated only a transient response to initial therapy with R-CHOP plus bortezomib, following which she had rapid disease progression, resulting in an overall survival of 10 months.

[CONCLUSION] For extranodal lymphomas, multisite sampling should be performed for a confirmed diagnosis to prevent misdiagnosis or oversight of concurrent lesions. This diagnostically challenging case highlights the importance of molecular testing for identifying and understanding the clonal evolution of lymphomas and suggests how immunophenotypic heterogeneity may lead to misdiagnosis. It also provides important insights into the biology of DLBCL-to-PBL evolution. These findings highlight the need for more precise molecular diagnostic tools and novel approaches to improve outcomes for patients with such highly aggressive lymphoma.