We analyzed the clinicopathological, cytogenetic, and molecular features of 18 primary cutaneous diffuse large B-cell lymphomas (PCDLBCLs) and 15 DLBCLs secondarily localized to the skin (SCDLBCLs), highlighting biological similarities and differences between the 2 groups. PCDLBCLs were subclassified after histopathological review as PCDLBCL-leg type (PCDLBCL-LT, 10 cases) and the PCDLBCL-not otherwise specified (PCDLBCL-NOS, 8 cases). Immunohistochemistry for Hans' algorithm markers, BCL2, and MYC was performed. The molecular study included the determination of the cell of origin (COO) by Lymph2Cx assay on NanoString platform, FISH analysis of IgH, BCL2, BCL6, and MYC genes, as well as the mutation analysis of MYD88 gene. In immunohistochemistry analysis, BCL2 and MYC hyperexpression was more frequent in LT than in NOS cases and, according to Hans' algorithm, PCDLBCL-LTs were mostly of the non-GC type (8/10), whereas in PCDLBCL-NOS, the GC type prevailed (6/8). The determination of COO using Lymph2Cx supported and further confirmed these results. In FISH analysis, all but one LT cases versus 5 of 8 PCDLBCL-NOS showed at least one gene rearrangement among IgH, BCL2, MYC, or BCL6. In addition, MYD88 mutations were more frequently present in LT than in NOS subtypes. Interestingly, MYD88-mutated patients were older, with a non-GC phenotype and had worse OS, compared to MYD88 WT cases. Overall, SCDLBCL did not show, at the genetic and expression level, different profiles than PCDLBCL, even if they bear a significantly worse prognosis. At survival analysis, the most important prognostic factors in patients with PCDLBCL were age and MYD88 mutation, whereas relapse and high Ki-67 expression were relevant in patients with SCDLBCL. Our study comprehensively analyzed the clinicopathological and molecular features of PCDLBCL-LT, PCDLBCL-NOS, and SCDLBCL, underlining the differences among them and the importance of properly identifying these entities at the time of diagnosis.
Keywords: Clinicopathological findings; Cytogenetic findings; Molecular findings; PCDLBCL; Primary cutaneous diffuse large B-cell lymphomas.
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