Mariani, Rachel

Large B-cell lymphoma with IRF4 rearrangement (LBCL-IRF4) predominantly affects children and young adults (CAYA) and presents as localized disease with excellent prognosis. Although most tumors harbor IRF4 rearrangements (IRF4-R), the existence of cryptic rearrangements has been suggested. Whether IRF4-R LBCL in adults represents the same biological entity remains unclear. To address this question, 35 CAYA patients diagnosed with LBCL-IRF4 and 7 adult (>40-year-old) LBCL with IRF4-R were investigated by an integrative molecular approach. Targeted sequencing structural variant analysis (SV-NGS) confirmed the IRF4-R in 84% of investigated cases. In CAYA, an enrichment (55% vs 29% in adults) of translocations involving IGH, with a breakpoint cluster 3' to IRF4 (EXOC2) was observed, including a cryptic insertion of IGHM-IGHJ5 into IRF4 locus. Novel translocations, IRF4::MIR142 in two CAYA (7%) and IRF4::BATF in one adult, were discovered. Whole-exome sequencing analysis identified unreported mutations in LBCL-IRF4 as YY1 and ZC3H12A (11% each). The high incidence of mutations affecting the B-cell receptor/NF-KB pathways in LBCL-IRF4 was confirmed in cases with diffuse component only. None of the CAYA tumors were classified by LymphGen tool. Adult IRF4-R LBCL showed higher levels of genetic complexity and a distinct mutational profile with mutations on KMT2D and DTX1 (43% each), and MYD88-L265P (29%), and were predicted as EZB or MCD (29% each). These differential genetic features were in line with different clinical presentations (extranodal involvement and advanced stage). In conclusion, IRF4-R architecture and mutational profile differ according to age, supporting that not all cases should be classified as LBCL-IRF4.

We report comprehensive characterization of an unusual collision tumor comprising extramedullary plasmacytomas and nasopharyngeal angiofibroma in a pediatric patient, which has yet to be reported. Histologically, the nasopharyngeal angiofibroma showed typical morphology with a diffuse, dense plasmacytic infiltrate in the stroma. The neoplastic plasma cells showed a spectrum of well-differentiated, plasmablastic, and anaplastic morphology, Epstein-Barr virus encoded RNA (EBER) positivity, and aberrant immunophenotype. Fluorescence in situ hybridization using a plasma cell myeloma targeted panel detected gains of 1q21.3 ( CKS1B, x3), 3q27 ( BCL6, x4), and 11q22.3 ( ATM, x3), but no rearrangement of ALK and MYC. A 50-gene next generation sequencing lymphoma panel failed to detect any pathogenic mutation. Plasmacytoma with EBER positivity and plasmablastic morphology must be distinguished from plasmablastic lymphoma due to different clinical management and prognosis. This case highlights the importance of a thorough pathological evaluation of a mass lesion with synchronous neoplastic processes.