Large B-cell lymphoma with IRF4 gene rearrangements: Differences in clinicopathologic, immunophenotypic and cytogenetic features between pediatric and adult patients.

Large B-cell lymphoma (LBL) with interferon regulatory factor 4 (IRF4) rearrangement (LBL-IRF4), a provisional entity in the 2017 WHO classification, primarily arises in children and young adults and has a favorable prognosis. However, few studies have addressed the clinicopathologic and cytogenetic features of older adults with IRF4-rearranged B-cell lymphomas. From a database of all internal and external cases (08/01/2015 to 12/01/2020) on which interphase fluorescence in situ hybridization was performed at the Mayo Clinic, we identified 43 patients with B-cell lymphoma and IRF4 rearrangements. Consistent features included large cell morphology, expression of CD20, BCL6, and MUM1, and absence of MYC-R. All pediatric cases (n = 12) arose in Waldeyer's ring (WR), cervical lymph node (CLN), or bowel, and lacked BCL6-R and BCL2-R, and all but one showed classic morphology. Adults with WR, CLN, or bowel involvement (n = 22) were younger (median 32 years). Their lymphomas resembled pediatric cases morphologically and lacked BCL2-R, although 30% harbored BCL6-R (P = 0.043). Lymphomas that involved other anatomic sites (n = 9) arose in older adults (median 68 years; P = 0.002) and often showed atypical morphology (P < 0.001). All lacked BCL6-R and 2 of 4 harbored BCL2-R (P < 0.001). LBL-IRF4 - arising in WR, CLN, or bowel may represent a distinct clinicopathologic entity characterized by pediatric/younger adult age, classic morphology, and lack of BCL2-R. In contrast, B-cell lymphomas with IRF4-R that arise in other sites usually involve older adults, are often morphologically atypical and/or harbor BCL2-R, and may be more akin to diffuse LBL, not otherwise specified.

Typical, atypical and cryptic t(15;17)(q24;q21) (PML::RARA) observed in acute promyelocytic leukemia: A retrospective review of 831 patients with concurrent chromosome and PML::RARA dual-color dual-fusion FISH studies.

The diagnosis of acute promyelocytic leukemia (APL) relies on the identification of PML::RARA fusion. While the majority of APL cases harbor a typical t(15;17)(q24;q21), atypical genetic mechanisms leading to the oncogenic PML::RARA fusion have been reported yet their frequency and scope remain poorly characterized. We assessed the genetic findings of 831 cases with APL investigated with concurrent chromosome banding analysis and dual-color dual-fusion fluorescence in situ hybridization (D-FISH) analysis at our institution over an 18.5-year timeframe. Seven hundred twenty-three (87%) cases had a typical balanced t(15;17) with both testing modalities. Atypical karyotypic results including complex translocations, unbalanced rearrangements and insertional events occurred in 50 (6%) cases, while 6 (0.7%) cases were cryptic by conventional chromosome studies despite PML::RARA fusion by D-FISH evaluation. Atypical FISH patterns were observed in 48 (6%) cases despite apparently balanced t(15;17) on chromosome banding analysis. Two hundred fifty (30%) cases displayed additional chromosome abnormalities of which trisomy/tetrasomy 8 (37%), del(7q)/add(7q) (12%), and del(9q) (7%) were most frequent. Complex and very complex karyotypes were observed in 81 (10%) and 34 (4%) cases, respectively. In addition, 4 (0.5%) cases presented as an apparently doubled, near-tetraploid stemline clone. This report provides the largest appraisal of cytogenetic findings in APL with conventional chromosome and PML::RARA D-FISH analysis. By characterizing the frequency and breadth of typical and atypical results through the lens of these cytogenetic testing modalities, this study serves as a pragmatic source of information for those involved in the investigation of APL in both the clinical and research laboratory settings.

Detection of a Cryptic KMT2A/AFDN Gene Fusion [ins(6;11)(q27;q23q23)] in a Pediatric Patient with Newly Diagnosed Acute Myeloid Leukemia.

KMT2A gene rearrangements are a major oncogenic driver in multiple hematologic neoplasms. Apart from t(9;11)(p21;q23) (KMT2A/MLLT3) in acute myeloid leukemia (AML), KMT2A gene rearrangements are considered to convey high risk and poor overall survival. Herein, we report a case of a 7 year old boy with newly diagnosed AML and a cryptic KMT2A/AFDN gene fusion resulting from a 5'KMT2A insertional event. The results of conventional chromosome studies revealed trisomy 8 in all 20 metaphases, with normal-appearing chromosomes 6 and 11. A KMT2A break-apart FISH probe identified 2 intact copies of the KMT2A gene region and an extra 5'KMT2A signal in 85% of interphase nuclei. Subsequent FISH studies using a KMT2A/AFDN dual-color dual-fusion FISH probe revealed positive results for a single fusion in 82% of interphase nuclei, indicating a KMT2A/AFDN gene fusion. Subsequently, metaphase FISH confirmed the location of the KMT2A/AFDN fusion at 6q27. To our knowledge, this represents only the second time in the literature that a cryptic KMT2A/AFDN gene fusion resulting from a 5'KMT2A insertional event was reported.

Identification of a novel KMT2A/GIMAP8 gene fusion in a pediatric patient with acute undifferentiated leukemia.

Acute undifferentiated leukemia (AUL) is a very rare hematologic neoplasm that expresses no markers specific for either myeloid or lymphoid lineages. While commonly observed in several acute leukemias, KMT2A rearrangements in AUL have been rarely reported in the literature. We report the third case to our knowledge of AUL harboring a KMT2A rearrangement. Furthermore, the KMT2A/GIMAP8 gene fusion identified in this case represents a novel KMT2A rearrangement.

Detection of a Cryptic EP300/ZNF384 Gene Fusion by Chromosomal Microarray and Next-Generation Sequencing Studies in a Pediatric Patient with B-Lymphoblastic Leukemia.

Zinc-finger protein 384 (ZNF384) gene fusions with EP300 have recently been described as a recurrent fusion in B-cell acute lymphoblastic leukemia (B-ALL) with a good response to conventional chemotherapy, suggesting a favorable prognosis. Herein, we report on a female patient aged 12 years with uninformative conventional chromosome and B-ALL panel fluorescence in situ hybridization studies with chromosomal microarray showing multiple copy number gains, including relative gains in the ZNF384 (12p13.31) and EP300 (22q13.2) gene regions, suggesting a cryptic EP300/ZNF384 fusion. Ultimately, a next-generation sequencing assay, mate pair sequencing, was utilized to confirm EP300/ZNF384 fusion in this B-ALL clone, which may confer a favorable overall prognosis and potential targeted therapy.