ALBERT

Description: Background: T-cell prolymphocytic leukemia (T-PLL) is a rare, mature T-cell neoplasm with poor prognosis. Only few T-PLL cases have been analyzed with regard to cytogenetic and molecular genetic aberrations so far. Therefore, we performed a comprehensive characterization of patients with T-PLL, including the identification of potential correlations between the respective markers and their impact on prognosis. Methods: The cohort comprised 47 T-PLL cases (32 male, 15 female). Median age was 69.8 years (range: 32.7-86.6 years). Diagnosis of T-PLL was assigned by immunophenotyping and cytomorphology. All 47 patients were further investigated using (i) chromosome banding analysis (CBA), (ii) interphase FISH to determine the copy number state for TP53 and ATM and chromosomal rearrangements of TCRA/D and TCL1 and (iii) array CGH. Next-generation amplicon deep-sequencing was performed to analyze mutations in ATM,BCOR, TP53 (n=47, respectively); JAK1 (n=44) and JAK3 (n=45) were analyzed by Sanger sequencing. Clinical follow-up data was available for 43 patients. Results: In all 47 cases, chromosomal abnormalities and/or molecular mutations were detected. Combining CBA and FISH data, an inv(14)(q11q32)/t(14;14)(q11;q32) was observed in 37/47 (78.7%) cases, a t(X;14)(q27;q11) in 3 cases (6.4%) and an i(8)(q10) in 17/47 (36.2%) cases. ATM deletions were detected in 27/47 (57.5%), TP53 deletions in 11/47 (23.4%) patients. Array CGH analyses revealed additional gains and losses of specific chromosomal regions, mainly affecting 7q (deletions in region 7q34-7q36; n=16), 12p (deletions in 12p12-12p13; n=11) and 22q (deletions in 22q11-q12 with a concomitant gain of 22q12-q13; n=8). Regarding molecular analyses, the most frequently mutated gene was ATM (34/47; 72.3%). Mutations in TP53 were found in 7/47 (14.9%) and in BCOR in 4/47 (8.5%) patients. Mutations of JAK1 were found in 3/44 (6.8%), and of JAK3 in 8/45 (17.8%) cases. ATM and TP53 frequently carried a mutation of one allele and a deletion of the other: 23/34 (67.6%) cases with ATM mutation also showed an ATM deletion and in 5/7 (71.4%) cases with TP53 mutation also a TP53 deletion was detected. Regarding chromosomal aberrations, all cases with i(8)(q10) harbored a TCRA/D rearrangement and an ATM mutation, whereas TP53 mutations were not present in any case with i(8)(q10). ATM mutations were found to be correlated to TCRA/D rearrangements (33/40 TCRA/D+ cases, 82.5%; 1/7 TCRA/D- cases, 14.3%; p60 years (n=34), JAK1 mutations (0/12 vs. 3/32) and mutations/deletions in the TP53 gene were detected exclusively in patients 〉60 years (TP53mut: 0/13 vs. 7/34; TP53del: 0/13 vs. 11/34). JAK3 mutations were also found predominantly in older patients (1/12; 8.3% vs. 7/33; 21.2%). Median overall survival (OS) was 27.4 months. No influence on OS was found for mutations and/or deletions of ATM, TP53, BCOR orJAK1 or aberrations of chromosomes 8 or 14. The age of patients was found to impact OS (median OS, ≤60 years: 29.0 months vs. 〉60 years: 15.9 months), although this was not significant (p=0.077). However, OS was found to be significantly shorter in patients with JAK3 mutation compared to patients without JAK3 mutation (median OS, 5.1 months vs. 29.1 months; p=0.009). Conclusions: Genetic abnormalities were revealed in all 47 cases with T-PLL. Two distinct genetic subgroups of T-PLL were identified: A large subset, comprising 81% of patients, showed abnormalities involving the TCRA/D locus activating the proto-oncogenes TCL1 (14q32) or MTCP1 (Xq28). This subgroup had higher frequencies of i(8)(q10) and of ATM mutations, while the second group was characterized by a higher frequency of TP53 mutations (figure). Further, JAK3 mutations were identified as an important prognostic marker, showing a significant negative impact on OS. Figure 1: Genetic abnormalities in T-PLL Figure 1:. Genetic abnormalities in T-PLL mut=mutation, del=deletion, TCRA/D=rearrangements involving TCRA/D, TCL1=rearrangements involving TCL1, MTCP1= rearrangements involving MTCP1 Disclosures Stengel: MLL Munich Leukemia Laboratory: Employment. Kern:MLL Munich Leukemia Laboratory: Employment, Equity Ownership. Zenger:MLL Munich Leukemia Laboratory: Employment. Perglerová:MLL2 s.r.o.: Employment. Schnittger:MLL Munich Leukemia Laboratory: Employment, Equity Ownership. Haferlach:MLL Munich Leukemia Laboratory: Employment, Equity Ownership. Haferlach:MLL Munich Leukemia Laboratory: Employment, Equity Ownership.

Description: Background: According to the revised WHO classification of 2016, AML with mutated RUNX1 constitutes a new provisional entity. We previously reported that the subgroup of RUNX1-mutated AML with RUNX1 wild-type (WT) loss is associated with a distinct pattern of cytogenetic and molecular genetic abnormalities and with an adverse prognosis. However, the impact of multiple RUNX1 mutations is unclear yet. Aims: Evaluation of associated genetic alterations and prognosis in AML with 〉1 RUNX1 mutation as compared to those with (1) RUNX1 WT loss and (2) one RUNX1 mutation. Patient cohorts and methods: The total cohort comprised 467 AML cases with RUNX1 mutations (mut) (296 male, 171 female). Median age was 72 years (range: 18-91 years). All patients were investigated using chromosome banding analysis (CBA) and amplicon sequencing of RUNX1. The cohort was split into the subgroups with RUNX1 WT loss (UPD or RUNX1 deletion detected by genomic arrays) (n=50), cases with 〉1 RUNX1mut (n = 94) and cases with 1 RUNX1mut and conservation of the RUNX1 WT allele (n = 323). Of these, 50, 55 and 58 cases, respectively, were selected for further mutation analyses of ASXL1, BCOR, CBL, CEBPA, DNMT3A, ETV6, EZH2, FLT3-ITD, FLT3-TKD, GATA2, IDH1, IDH2, KIT, KRAS, MLL-PTD, NPM, NRAS, SETBP1, SF3B1, SRSF2, TET2, TP53, U2AF1 and WT1. Variants of unknown significance were excluded from statistical analysis. Results: In the total cohort of 467 cases, CBA revealed a normal karyotype (NK) in 53% of patients, 18% harbored trisomies, 3% showed a complex karyotype (〉3 abnormalities), 26% other aberrations. The proportion of cases with trisomies was largest in cases with RUNX1 WT loss (26%), followed by 〉1 RUNX1mut (19%) and 1 RUNX1mut (16%). In more detail, in the total cohort, 56% of cases with trisomies harbored +8, in 30% +13 was found. A similar pattern was observed for 1 RUNX1mut, whereas in cases with WT loss +13 was the most abundant trisomy (+8: 66% in 1 RUNX1mut vs. 31% in WT loss, p=0.022; +13: 15% vs. 62%, p1 RUNX1mut showed an intermediate distribution (+8: 44%, +13: 50%). Missense mutations were the most abundant mutation type (53%) inWT loss cases, followed by frameshift mutations (28%). By contrast, in cases with 1 RUNX1mut, frameshift mutations were found more frequent (45%, p=0.016), whereas missense mutations were detected at a frequency of 31% (p=0.006). In cases with 〉1 RUNX1mut, both were observed at similar frequencies (missense: 36%, frameshift: 38%). Mutation analyses of 163 selected cases revealed SRSF2 (39%), ASXL1 (36%), DNMT3A (19%), BCOR (18%), IDH2 (17%), SF3B1 (17%) and TET2 (17%) mutations as most frequently mutated genes in the total cohort. Cases with RUNX1 WT loss showed a higher frequency of ASXL1mut compared to the other cases (50% vs. 29%, p=0.013), while U2AF1mut were absent from this group (0% vs. 15%, p=0.019). Differences between cases with and without RUNX1 WT loss were also detected for DNMT3A, TET2, SF3B1 (more abundant in WT loss) and IDH2, WT1 (less abundant in WT loss), although these were not statistically significant. For many genes, the group of cases with 〉1 RUNX1mut showed an intermediate abundance pattern, or mutation frequencies similar to cases with 1 RUNX1mut were observed. Mutations in spliceosome genes (SF3B1, SRSF2, U2AF1, ZRSR2) were very abundant in all subgroups but less frequent (although not statistically significant) in cases with 1 RUNX1mut. Median overall survival (OS) in the total cohort was 14 months. WT loss (OS: 5 months) and 〉1 RUNX1mut (14 months) showed an adverse impact on prognosis compared to 1 RUNX1mut (22 months; p=0.002 and p=0.048, respectively). Mutations in ASXL1 and KRAS showed a negative impact on OS in the total cohort (10 vs. 18 months, p=0.028; 1 vs. 15 months, p1 RUNX1mut show a pattern intermediate between the former two subgroups. 4) Loss of RUNX1 WT and 〉 1 RUNX1mut showed an adverse impact on OS. Thus, not only the presence and number of RUNX1mut but also the conservation of an intact RUNX1 allele is biologically and clinically relevant. Disclosures Stengel: MLL Munich Leukemia Laboratory: Employment. Kern:MLL Munich Leukemia Laboratory: Employment, Equity Ownership. Meggendorfer:MLL Munich Leukemia Laboratory: Employment. Perglerová:MLL2 s.r.o.: Employment. Haferlach:MLL Munich Leukemia Laboratory: Employment, Equity Ownership. Haferlach:MLL Munich Leukemia Laboratory: Employment, Equity Ownership.

Description: Background: CLL is characterized by a distinct pattern of translocations, genomic gains and losses and molecular mutations. The most frequent abnormalities such as trisomy 12 and deletions of 6q, 11q, 13q and 17p have been intensively studied. However, data on less frequent recurrent abnormalities such as the partial gain of the short arm of chromosome 2 is lacking. Aims: a) Determine the frequency of 2p gain in CLL, b) Characterize the size and the commonly gained region, c) Analyze the spectrum of additional cytogenetic abnormalities and molecular mutations, and d) Evaluate the prognostic impact. Patients and Methods: Chromosome banding analysis (CBA) revealed a gain of 2p in 113 out of 5564 (2%) CLL cases. In 72 cases with sufficient material genomic array analysis (SurePrint G3 ISCA CGH+SNP Microarray, Agilent, Waldbronn, Germany) and determination of the mutation status of TP53, SF3B1 and IGHV were performed. Results:76% of patients with gain of 2p were male. The median WBC count was 33,700/µL (range: 5,900 - 228,000). Median age was 66 years (range: 29 - 87). The gain of 2p always encompassed the 2p telomere (2pter) while the centromeric border of the 2p gain varied between 2p21 and the centromere of chromosome 2 (2p10) (genomic positions 45,859,076 to 92,297,003). The gain of 2p was the sole chromosomal abnormality in only 8/72 cases (11%) and was accompanied by one, two or more than two additional aberrations in 10, 20, and 34 cases. In total 209 chromosome abnormalities were observed in addition to the 2p gain (median per patient: 2, range: 0-16). Of these only 21 were balanced while 188 were unbalanced abnormalities leading to gain or loss of chromosomal material. Gain of 2p was most frequently accompanied by deletions in 13q (total: 74%, homozygous: 11%), 11q (56%), 18p (18%), and 6q (13%) and gains of 8q (11%). 17p deletions were present in 6% of cases. In 49 cases (68%) the gain of 2p was present in the main clone while it was present in a subclone only in 23 cases (32%). The gain of 2p material was due to a duplication in the short arm of chromosome 2 in 10 cases, while a gain of an isochromosome 2p was present in 3 cases. In the remaining cases material of the short arm of chromosome 2p was attached to a variety of different partner chromosomes. The most frequent acceptor chromosome was chromosome 18 (n=13; 18%). In two cases (2%) 2 IGH rearrangements were observed of which one was mutated and the other unmutated. The IGHV status was unmutated (IGHV-U) in 66 (92%) and mutated in only 4 cases (6%). Three of these 4 cases with mutated IGHV showed only a low mutation rate (sequence homology to germline 97-97.9%). Stereotyped B-cell receptors were present in 14 cases (19%). SF3B1 mutations were observed in 21 cases (29%) with a median mutation load (ML) of 39% (range: 10-51%). TP53 mutations were detected in 8 (11%) cases (median ML: 60%, range: 13-100%). In 2 patients with a TP53 mutation a TP53 deletion was present and in 3 cases a copy neutral loss of heterozygosity (CN-LOH) of 17p was detected leading to TP53 wild-type loss in these 5 cases. TP53 mutations were less frequent in cases harboring the gain of 2p as the sole abnormality (3% vs 21%, p=0.02) The prognostic impact of 2p gain was evaluated in an unselected cohort of 1381 CLL cases with available follow up data (median follow up: 5.1 years) including 22 cases with 2p gain. The frequency of IGHV-Ustatus, SF3B1 mutations and 11q/ATM deletions was significantly higher in CLL with 2p gain compared to cases without (for all p

Description: Background: TP53 is altered in ~50% of human cancers. Alterations include mutations and deletions. Both frequently occur together, supporting the classical "two-hit" hypothesis for tumor-suppressor genes. Aim: Comparison of TP53 mutation/deletion patterns in different hematological malignancies, including AML, MDS, ALL, Burkitt lymphoma, CLL and T-PLL. We analyzed (i) the frequencies of TP53 mutations and deletions, (ii) the types of mutation, (iii) the mutation load, (iv) the correlations to cytogenetic aberrations, (v) the age dependency, and (vi) impact on survival. Patient cohort and methods: A total of 3383 cases (AML: n=858, MDS: n=943, ALL: n=358, Burkitt lymphoma: n=25, CLL: n=1148 and T-PLL: n=51) were analyzed for TP53 deletions by interphase FISH determining the copy number state and for TP53 mutations by next-generation amplicon deep sequencing. Karyotype data was available for all cases. Results: Overall, alterations in TP53 were detected in 361/3383 cases (11%; 186 cases with mutation only (mut only), 51 cases with deletion only (del only), 124 cases with mutation and deletion (mut+del)). Regarding the respective entities, the highest frequency of TP53 alterations was observed in patients with Burkitt lymphoma (total alteration frequency: 56%, mut+del: 12%, mut only: 44%, no case del only). Alterations in TP53 also occured with a high incidence in patients with T-PLL (total: 30%; mut+del: 10%; mut only: 4%; del only: 16%) followed by cases with ALL (total: 19%; mut+del: 6%; mut only: 8%; del only: 5%) and AML (total: 13%; mut+del: 5%; mut only: 7%; del only: 1%). By contrast, TP53 alterations occurred less frequently in patients with CLL (total: 8%; mut+del: 4%; mut only: 3%; del only: 1%) and MDS (total: 7%; mut+del: 1%; mut only: 5%; del only: 1%). Missense mutations were found to be the most abundant mutation type in all entities analyzed with a frequency ranging from 71% - 88%. In all entities mainly one mutation per case was detected; however, MDS cases were found to harbour a statistically increased proportion of cases with two mutations compared to the other entities (p = 0.003). High TP53 mutation loads were detected in T-PLL (median: 88%) and AML (47%), whereas the lower ones were found in ALL (28%), Burkitt lymphoma (39%), MDS (39%), and CLL (36%). A strong correlation of TP53 alterations with a complex karyotype was observed in AML (of patients with TP53 alteration: 5% with normal karyotype, 67% with complex karyotype, 28% with other aberrations), ALL (16% normal, 45% complex, 39% other), MDS (14% normal, 53% complex, 33% other), and T-PLL (20% normal, 47% complex, 33% other). By contrast, in CLL and Burkitt lymphoma, TP53 alterations were mainly correlated with other aberrations (CLL: 10% normal, 30% complex, 60% other; Burkitt: 29% normal, 0% complex, 71% other). TP53 mut and TP53 mut+del were significantly more frequent in patients ≥ 60 vs 〈 60 years in AML (9% vs. 2% for mut only, p 〈 0.001; 7% vs. 2% for mut+del, p = 0.001) and ALL (12% vs. 6% for mut only, p 〈 0.001; 13% vs. 3% for mut+del, p = 0.001). By contrast, no such differences were observed for patients with CLL, MDS, T-PLL and Burkitt lymphoma. Moreover, TP53 alterations (especially of TP53 mut+del) had a significant negative impact on OS in all entities except for T-PLL and Burkitt lymphoma, most probably due to their overall short OS or due the lower number of cases. Conclusion: The frequency of TP53 mutations and/or deletions as well as the mutation load clearly varied between different hematological malignancies with the highest incidence of TP53 mut in patients with Burkitt lymphoma (56%) and a rather low frequency in CLL (7%) and MDS (6%). TP53 del were frequent in patients with T-PLL (26%) and Burkitt lymphoma (12%) and are hardly found in MDS cases (2%). TP53 alterations are correlated to higher age in AML and ALL. Moreover, alterations in TP53 are correlated to a short OS and to a complex karyotype, with the exception of Burkitt lymphoma and CLL, were they were found to be associated to other cytogenetic aberrations. Thus, TP53 mutations and deletions need further investigation in the future, especially regarding their clinical impact in different hematologic entities. Disclosures Stengel: MLL Munich Leukemia Laboratory: Employment. Kern:MLL Munich Leukemia Laboratory: Employment, Equity Ownership. Haferlach:MLL Munich Leukemia Laboratory: Employment, Equity Ownership. Schnittger:MLL Munich Leukemia Laboratory: Employment, Equity Ownership. Zenger:MLL Munich Leukemia Laboratory: Employment. Haferlach:MLL Munich Leukemia Laboratory: Employment, Equity Ownership.

Description: Background: Persistent polyclonal B-cell lymphocytosis (PPBL) is a rare disorder, occurs almost exclusively in smoking women and is characterized by a chronic polyclonal lymphocytosis with circulating binucleated lymphocytes, clonal cytogenetic abnormalities involving chromosome 3, and chromosomal instability. Outcome of PPBL patients is mostly benign, but subsequent malignancies (non-Hodgkin´s lymphomas and solid tumors) were described. Potential molecular factors leading to their development are yet unclear. Aims: Detailed molecular genetic characterization of PPBL by whole genome sequencing (WGS) and RNA sequencing (RNAseq) in comparison to the well-characterized lymphoid malignancy CLL. Patient cohorts and methods: The total cohort comprised 27 PPBL (3 male, 24 female) and 250 CLL cases (163 male, 87 female). WGS was performed for all patients: 150bp paired-end reads where generated on Illumina HiseqX and NovaSeq 6000 machines (Illumina, San Diego, CA). A mixture genomic DNA from multiple anonymous donors was used as normal controls. To remove potential germline variants, each variant was queried against the gnomAD database, variants with global population frequencies 〉1% where excluded. Final analysis was performed only on protein-altering and splice-site variants. For further analysis, a virtual panel of 355 lymphoid genes was selected. All reported p-values are two-sided and were considered significant at p 5 CPM) in at least 66% of the samples. Genes with FDR (false discovery rate) 〈 0.05 and an absolute logFC 〉 1.5 were considered differentially expressed (DE). Results: Median age was 46 years for PPBL patients (range: 23-67 years) and 67 years for CLL patients (range: 39-94 years). Mean number of mutations per patient was 18 for PPBL and 20 for CLL. For both entities, the majority of mutations were missense mutations (88% in PPBL vs. 81% in CLL), followed by splice-site mutations (7% vs. 10%), other mutation types were only rarely detected. In PPBL, 42 genes were found to be mutated at a frequency of 〉15%, including ATM (22%), CREBBP (19%), NCOR2 (19%), AHNAK2 (15%), JAK3 (15%), NOTCH2 (15%) and TRAF1 (15%), all of which have been associated with a variety of cancers. Moreover, ATM, NOTCH2 and TRAF1 mutations were described before to be associated with lymphomas. In PPBL patients, mutations in TRAF1 and ATM as well as mutations in TRAF1 and NOTCH2 were found to be mutually exclusive. For CLL patients, 29 genes showed a mutation frequency of 〉15%, comprising ATM (26%), KMT2D (23%), NOTCH1 (23%), LRP1B (19%), TP53 (16%) and CREBBP (15%). Comparison of the mutation frequencies between the two entities revealed several genes with significant differences: whereas mutations in CKAP5 (11% vs. 2%, p=0.022), DNMT3A (11% vs. 3%, p=0.033), MAP2 (19% vs. 4%, p=0.009), ROBO1 (15% vs. 4%, p=0.046) and TRAF1 (15% vs. 2%, p=0.006) were found to be more frequent in PPBL cases compared to CLL cases, KMT2D (4% vs. 23%, p=0.014), TDRD6 (0% vs. 14%, p=0.032) and TP53 (4% vs. 16%, p=0.048) mutations were more abundantly detected in CLL patients. Moreover, NOTCH1 was mutated more frequently in CLL cases (7% vs. 23%, p=0.082), whereas mutated NOTCH2 (known to be frequently mutated in splenic marginal zone lymphoma), was more abundant in PPBL patients (15% vs. 6%, p=0.116), although both correlations were not statistically significant. Gene expression analyses by RNAseq revealed 337 genes to be differentially expressed between the entities. 207 genes were upregulated in PPBL, including PTPRK, CXCR1, BCL11B, CEPBA, CCR4 and MYC, whereas 130 genes were found to be upregulated in CLL cases, comprising ID3, BCL2, FGF2 and FLT1. Conclusions: 1) WGS analysis identifies high frequencies of cancer/lymphoma-associated gene mutations in PPBL, including mutated ATM, NOTCH2 and TRAF1. 2) Five genes showed a higher mutation frequency compared to CLL including TRAF1,DNMT3A, CKAP5 and MAP2. 3) Lymphoma associated genes (BCL11B and MYC) were overexpressed in PPBL vs CLL. 4) Taken together our results question PPBL as a benign entity and identify molecular markers that might contribute to development of subsequent malignancies. Disclosures Stengel: MLL Munich Leukemia Laboratory: Employment. Höllein:MLL Munich Leukemia Laboratory: Employment. Kern:MLL Munich Leukemia Laboratory: Employment, Equity Ownership. Meggendorfer:MLL Munich Leukemia Laboratory: Employment. Haferlach:MLL Munich Leukemia Laboratory: Employment, Equity Ownership. Walter:MLL Munich Leukemia Laboratory: Employment. Hutter:MLL Munich Leukemia Laboratory: Employment. Haferlach:MLL Munich Leukemia Laboratory: Employment, Equity Ownership.

Description: The WHO recognizes tMN as a distinct disease entity. The majority of tMN arise after treatment of solid tumors with cytotoxic chemotherapy or radiation therapy. In many tMN patients, clonal hematopoiesis was demonstrated to be already present at diagnosis of the solid tumor and later gave rise to the tMN. Cases of tMN following successful treatment of AML are rare and poorly characterized. We therefore set out to study the genetic profile of these patients and evaluated if AML and subsequent tMN are two genetically distinct diseases or share a common ancestral clone. We selected cases of AML sent to our laboratory for diagnostic work-up from 2005 to 2018 who subsequently developed a tMN. To exclude events of AML relapse from the cohort, known AML driver mutations such as in NPM1 or AML defining rearrangements present at diagnosis (Dx) of AML had to be absent at Dx of tMN. Based on sample availability, whole exome sequencing (WES) was carried out for 25 pts at the time points of Dx of AML and Dx of tMN as well as on matched remission samples that were available for 19 pts. Enrichment based library preparation was performed using the xGen Exome Research Panel and sequenced (2x151bp) on a NovaSeq instrument. Data was processed with BaseSpace using the BWA Enrichment app with BWA for Alignment (against hg19) and GATK for variant calling with default parameters. Data was subsequently loaded into BaseSpace Variant Interpreter to filter and prioritize variants of interest. Only passed protein changing variants were considered with an ExAC population frequency of less than 1% for further analysis. The cohort included 13 females and 12 males, aged 28 to 77 years (median: 60 yrs). Median time to Dx of tMN following Dx of AML was 42 months (range: 8-96 months). Thirteen pts had developed tMDS and 12 pts tAML. While WES identified numerous recurrently mutated genes, we focused our further analyses on 28 genes associated with myeloid neoplasms and detected a total of 97 mutations (1-8 mutations per patient, median: 4). Following genes were mutated in 〉15% of pts: NPM1 (14/25 of pts), DNMT3A (9/25), TET2 (9/25), SRSF2 (7/25), CEBPA (6/25), RUNX1 (6/25), ASXL1, FLT3, IDH2 and TP53 (4/25 of pts, each). We did not identify a mutation pattern distinguishing between pts who developed a tAML or tMDS, however, pts with tAML had a significantly higher total number of mutations than those with tMDS (median of 5 vs 3 mutations, p= 0.022). When comparing matched initial AML and subsequent tMN samples for each patient, a total of 43 mutations were detected at Dx of AML only, while 25 mutations were exclusive to the tMN sample. Interestingly, 18/25 (72%) of pts harbored mutations present at both time points (Figure 1). Moreover, in 8/22 of pts with available material, mutations in DNMT3A (n=6), IDH1, SRSF2 and TET2 (n=1, each) persisted during remission. Of the 7 pts without shared mutations between time point of AML and tMN, 2 were initially positive for the PML-RARA rearrangement, and 1 patient showed a CBFB-MYH11 rearrangement at Dx of AML. Next, we compared gene mutation data with cytogenetic information available for 21/25 pts at both time points. Nine patients with a normal karyotype (NK) at Dx of AML developed chromosome aberrations at Dx of tMN. In this group, 8/9 pts harbored mutations in epigenetic modifiers (DNMT3A, TET2 and SRSF2) present both at AML and tMN. Similarly, 2/3 patients with NK AML and NK tMN shared mutations in IDH2, SRSF2 and ASXL1 at both time points. Eight pts showed either independent cytogenetic aberrations between AML and tMN or harbored chromosome aberrations at Dx of AML that were absent at Dx of tMN. Even in this group of cytogenetically independent clones, 3/8 pts harbored the same mutations at both time points. Our study provides novel insights into the pathogenesis of tMN. In the majority of analyzed cases, we detected mutations present in the AML and tMN clones of the same patient. Considering the absence of known AML driver gene mutations such as in NPM1 in the tMN sample, we speculate the presence of a common ancestral clone with mutations mostly affecting epigenetic modifiers which have previously been linked to clonal hematopoiesis. Unlike the full-blown leukemia, this clone is refractory to chemotherapy and later gives rise to the tMN. The absence of shared mutations between AML and tMN in patients with PML-RARA or CBFB-MYH11 rearrangement is in line with thought that these entities are true de novo AML that do not evolve from a clonal hematopoiesis. Disclosures Hartmann: MLL Munich Leukemia Laboratory: Employment. Nadarajah:MLL Munich Leukemia Laboratory: Employment. Meggendorfer:MLL Munich Leukemia Laboratory: Employment. Höllein:MLL Munich Leukemia Laboratory: Employment. Vetro:MLL Munich Leukemia Laboratory: Employment. Stengel:MLL Munich Leukemia Laboratory: Employment. Kern:MLL Munich Leukemia Laboratory: Employment, Equity Ownership. Haferlach:MLL Munich Leukemia Laboratory: Employment, Equity Ownership. Haferlach:MLL Munich Leukemia Laboratory: Employment, Equity Ownership.

Description: Key Points TP53 mutations are detected in 15.7% of patients with ALL and are correlated to a low hypodiploid karyotype and to MYC-translocations. Disruption of both TP53 alleles is associated with adverse prognosis in ALL.

Description: Background: The pathogenesis of secondary hematological neoplasms occurring after a primary hematological neoplasm and the relationship between both is still unclear. We set up this study in order to evaluate whether both diseases share genomic alterations. Patients and Methods: We selected 25 patients who were diagnosed with a first hematological neoplasm (FHN) (CLL: n=14, other mature B cell neoplasm: n=6, AML: n=4, CML: n=1) and in median 48 months later (range: 16-119) with a second hematological neoplasm (SHN) (t-MDS: n= 21; t-AML: n=1, CMML: n=1; t-MPN: n=1, t-MDS/MPN: n=1). In 9 cases bone marrow was available that had been drawn in complete cytomorphological remission (CR) between FHN and SHN. Whole genome sequencing was performed for all 59 samples: 150 bp paired-end sequences where generated on Illumina HiseqX and NovaSeq 6000 machines (Illumina, San Diego, CA, USA) (median coverage 106x). A mixture of genomic DNA from multiple anonymous donors was used as normal controls. The overlap of genomic alterations present at the different points in time was evaluated. For the assessment of mutations as germline the following parameters were considered: a) variant allele frequency (VAF) 0.4-0.6; b) gnomAD frequency