Primary cutaneous blastic marginal zone lymphoma: A comprehensive clinical, light microscopic, phenotypic and cytogenetic appraisal

Background: Primary cutaneous marginal zone lymphoma (PCMZL) is a form of indolent lymphoproliferative disease where the disease is largely a cutaneous confined process. It is typically a neoplasm composed of post germinal small B-cells and light chain restricted plasma cells in a background of reactive T-cell hyperplasia and benign germinal centers. Rarely a significant degree of large cell infiltration occurs warranting the categorization as blastic marginal zone lymphoma.Materials and methods: We reviewed our data base over a time period of 2016 to 2022 for cases diagnosed as blastic MZL. Twelve cases were identified. The clinical records and pathological data were reviewed. Results: Nine of the cases represented de novo forms of blastic MZL while in three cases there was a prior history of MZL. Multifocal cutaneous disease was not uncommon and one quarter of the cases had evidence of extracutaneous dissemination. All patients except three achieved remission with varied therapeutic interventions depending on the extent of the disease ranging from conservative re-excision to chemotherapy. No patient died from lymphoma. Light microscopically, there was evidence of a background of conventional MZL in the majority of cases. The large cell component was typically characterized by multiple micronodular aggregates throughout the dermis although in three cases there was a striking diffuse large cell component as the dominant infiltrate. Phenotypically, a third of the cases showed either CD5 or CD23 positivity amidst neoplastic B cells. Significant staining for BCL-2 was noted in the majority of cases tested while extensive MUM-1 positivity was observed in half of the cases tested. Kappa or lambda light chain restriction was seen in most. The Ki67 proliferation index exceeded 30 % in all cases. There was C-MYC positivity in two cases. While most cases did not detect cytogenetic abnormalities, one case had multiple cytogenetic hits that are associated with diffuse large B cell lymphoma. Next generation sequencing showed a Ten-eleven translocation 2 mutation in the earlier biopsy prior to transformation and in the later biopsy after transformation along with an additional B2M mutation in the transformed biopsy. Both types of mutations are very uncommon but held to contribute to tumor progression in the setting of diffuse large B cell lymphoma.Conclusion: Blastic MZL is associated with a more aggressive clinical course. Even when there is disseminated disease patients while not always cured did not have a fatal course in this series. The light microscopic findings are reproducible. The background of MZL, identification of larger cells in significant numbers without a follicle center phenotype, at times expressing CD5 or CD23 with variable positivity for MUM1, BCL-2 and C-MYC and a high proliferation index define the pathology in most. Certain cytogenetic abnormalities and genetic mutations implicated in large cell transformation into a diffuse large B cell lymphoma are seen in blastic MZL with earlier biopsies prior to transformation potentially harboring at risk genetic mutations.