Fielding, Adele K.

We previously showed that both reactive oxygen species-inducing chemotherapy and some genetic subtypes of B precursor acute lymphoblastic leukaemia (ALL) can induce bone marrow (BM) mesenchymal stromal cells (MSC) to become cancer associated fibroblasts (CAFs). Exposure of MSC to ALL-cell conditioned media (CM) is sufficient to generate CAFs - direct cell-cell contact is not required (Burt, Dey et al, 2024). We showed that CAFs can lead to chemoresistance via transfer of mitochondria to ALL cells through tunnelling nanotubes (Burt, Dey et al 2019). We noted that CAFs in the ALL BM had features of senescence, prompting the current study in which we aimed to investigate the link between senescence and CAFs in ALL. We used 3 genetic subtypes of ALL; BCR::ABL1 (SD1 cells, representing “adult” ALL) , ETV6::RUNX1 (REH cells, representing “childhood” ALL) and KMT2A::AFF1 (SEM cells, known from our previous work NOT to induce CAFs). We exposed HS27a stromal cells to the ALL CM at a number of timepoints over a period of three weeks and characterised senescence using qPCR, cytochemical B-galactosidase assays, flow cytometry and immunofluorescence (IF). Cytokine arrays were performed to quantify the senescence associated secretory phenotype (SASP) components and assess the complexity of SASP components in all three ALL subtypes. A more prolonged exposure (> 10 days) to CM was required for senescence to develop in contrast to CAF formation which occurs early (2-3 days) in HS27a MSC cells. Senescence marker expression peaked at around day 11 to day 14 of CM exposure before subsiding to lower levels around day 21. On day 14, 70% of HS27a cells treated with SD1 CM were positive for beta galactosidase compared to below 25% positive for REH and SEM cells. Cell cycle arrest was demonstrated by P16 and Ki67 IF. 95% of SD1 CM treated HS27a cells were positive for P16 compared to less than 10% in RPMI control. Likewise, only 29% of HS27a exposed to SD1 CM were Ki67 positive compared to 66% in the RPMI control. Expression levels of other senescence-associated markers such as SERPINE1, SERPINB2, SOD2, NFKB1 were quantified by qPCR and were all significantly (p<0.001) upregulated in SD1 CM treated HS27a (2 to 40 fold) compared to SEM CM (-2 to 5 fold) and REH CM (-0.5 to 1.0) treated HS27a. SASP associated cytokines IL6 (1000-5000pg/ml), IL8 (2500-5000pg/ml), CXCL10 (500-1500pg/ml), CCL5 (1500-2250pg/ml), IL10 (25-50pg/ml), were significantly (p<0.0001) upregulated in the SD1 CM treated HS27a compared to controls and other ALL cell line exposed HS27a. Finally, HMGB2 and LMNB1 genes, loss of which is associated with senescence were significantly (p<0.001) downregulated in the SD1 CM (-2.5 to 0.5 fold) treated HS27a compared to controls. In view of the prominence of senescence in SD1-exposed HS27a cells, we tested the effects of two different senolytic drugs venetoclax (BCL2i) and navitoclax (BCL2i/BCLXLi) in vitro. Briefly, HS27a cells were exposed to SD1 CM for 11 days, and after washing, increasing concentrations of the drugs were added for up to 72 hrs followed by washing, fixing and DAPI-staining and counting. HS27a exposed to SD1 CM was highly sensitive to low dose treatment of navitoclax (0.5uM) with 80% cell death 48 hrs post treatment. HS27a cells exposed to SD1 CM were less sensitive to venetoclax with only 50% cell death observed at higher doses (5uM) even after 72 hrs post treatment. Further senolytic drug screening experiments are ongoing. Our data suggest that BCR::ABL1 but not ETV6::RUNX1 or KMT2A::AFF1 ALL cells, can induce paracrine senescence in HS27a MSC cells. We suggest that paracrine senescence in the stromal microenvironment may be a component of treatment response in B-ALL. ^^ and ** contributed equally

Abstract Genomic classification has improved risk assignment of pediatric, but not adult B-lineage acute lymphoblastic leukemia (B-ALL). The international UKALLXII/ECOG-ACRIN E2993 (#NCT00002514) trial accrued 1229 adolescent/adult patients with BCR-ABL1− B-ALL (aged 14 to 65 years). Although 93% of patients achieved remission, 41% relapsed at a median of 13 months (range, 28 days to 12 years). Five-year overall survival (OS) was 42% (95% confidence interval, 39, 44). Transcriptome sequencing, gene expression profiling, cytogenetics, and fusion polymerase chain reaction enabled genomic subtyping of 282 patient samples, of which 264 were eligible for trial, accounting for 64.5% of E2993 patients. Among patients with outcome data, 29.5% with favorable outcomes (5-year OS 65% to 80%) were deemed standard risk (DUX4-rearranged [9.2%], ETV6-RUNX1/-like [2.3%], TCF3-PBX1 [6.9%], PAX5 P80R [4.1%], high-hyperdiploid [6.9%]); 50.2% had high-risk genotypes with 5-year OS of 0% to 27% (Ph-like [21.2%], KMT2A-AFF1 [12%], low-hypodiploid/near-haploid [14.3%], BCL2/MYC-rearranged [2.8%]); 20.3% had intermediate-risk genotypes with 5-year OS of 33% to 45% (PAX5alt [12.4%], ZNF384/-like [5.1%], MEF2D-rearranged [2.8%]). IKZF1 alterations occurred in 86% of Ph-like, and TP53 mutations in patients who were low-hypodiploid (54%) and BCL2/MYC-rearranged (33%) but were not independently associated with outcome. Of patients considered high risk based on presenting age and white blood cell count, 40% harbored subtype-defining genetic alterations associated with standard- or intermediate-risk outcomes. We identified distinct immunophenotypic features for DUX4-rearranged, PAX5 P80R, ZNF384-R/-like, and Ph-like genotypes. These data in a large adult B-ALL cohort treated with a non–risk-adapted approach on a single trial show the prognostic importance of genomic analyses, which may translate into future therapeutic benefits.

Abstract Background: Pre-treatment cytogenetics is a known predictor of outcome in haematological malignancies. However, its value in adult ALL is generally limited to the presence of the Philadelphia (Ph) translocation; mostly due to the low incidence of other recurrent chromosomal abnormalities. Methods: Since 1993, cytogenetic data from patients enrolled on a joint MRC/ECOG trial have been collated and reviewed centrally in the UK and US. Karyotype data from patients registered before the Imatinib amendment were pooled using standard cytogenetic definitions and classification criteria. Results: A successful cytogenetic result was achieved in 938/1235 (76%) cases; while 297 (24%) failed with <20 normal metaphases analyzed. Patients were classified into the following mutually exclusive groups: t(9;22)(q34;q11) n=193(21%); t(4;11)(q21;q23) n=50(5%); other MLL translocations n=11(1%), t(8;14)(q24;q32) and variants n=14(1%); t(1;19)(q23;p13) n=23(2%); T cell receptor translocations n=35(4%); low hypodiploidy (30–39 chromosomes) /near triploidy n=23(2%); high hyperdiploidy n=83(9%); tetraploidy n=12(1%); complex karyotype (>=5 aberrations) n=48(5%); other abnormal n=255(27%); normal n=191(20%). MRC and ECOG patients showed similar cytogenetic distributions, except for t(9;22), which was significantly more prevalent in the ECOG cohort (27% v 18%, p<0.001). However, the incidence of t(9;22) increased with age and ECOG patients were significantly older. Overall, the 5 year event free survival (EFS) was 32% (95% CI 30%–35%) with a median follow-up time of 5.1 years and did not differ between the two cohorts. The EFS of t(9;22) patients [15% (11%–21%)] was significantly inferior compared with all other cases [36% (32%–39%)] (p<0.001) and was independent of age and white cell count (WCC). Univariate logrank analyses identified t(4;11) and high hyperdiploidy as indicators of poor and good prognosis, respectively, compared with other Ph negative cases, but neither was independent of age and WCC. Three subgroups were shown to have a significantly worse EFS compared to other Ph negative cases by logrank analyses after adjusting for age and WCC: t(8;14) 14% (2%–37%) v 36% (32%–40%) (p=0.01); low hypodiploidy 22% (8%–40%) v 36% (32%–40%) (p=0.02); complex karyotype 21% (10%–33%) v 32% (29%–35%) (p=0.005). Neither of the latter two subgroups were associated with other poor risk features such as age, WCC or failure to achieve a remission within 4 weeks. Conclusions: This is the largest cytogenetic dataset of adult ALL reported to date and demonstrates the importance of combining cohorts to increase the number of cases available for analysis. The observation that low hypodiploidy and, for the first time, karyotype complexity confer a poor risk, demonstrates that cytogenetic subgroups other than the Ph translocation can and should be used to risk stratify adults with ALL to alternative treatments.

Abstract The UKALLXII/ECOG2993 international study for adults with acute lymphoblastic leukeamia (ALL) included a separate, single-arm study (still open) to evaluate the role of etoposide/TBI conditioned allogeneic bone marrow transplantation (BMT) in patients with Philadelphia chromosome positive (Ph pos) disease. Patients received 2 phases of induction, intensification with high dose methotrexate and BMT using unrelated donor stem cells where a matched sibling was not available. 267 patients with Ph pos ALL were treated from 1993 onwards, in the pre-imatinib era. The study was amended in 2003 to add imatinib 600mg per day following induction and after BMT for 2 years or until relapse. A subsequent amendment at the end of 2005, added imatinib 600mg per day also to phase 2 of induction. 153 patients have now been treated on the imatinib-containing protocol − 89 received imatinib following induction and 64 started imatinib with phase 2 induction. Complete remission (CR) rate at the end of 2 phases of induction was 91% with imatinib started in induction, 81% with imatinib started in consolidation only & 83% in the pre imatinib era. 128 of the 153 patients treated with any imatinib were eligible for BMT. Of the 98 patients with over 6 months follow-up, 57 (58%) actually received BMT. This transplant rate does not differ from the 62% in the pre-imatinib era although the data pertain mostly to those whose imatinib started later during therapy. Overall survival of the imatinib-treated group as a whole is 23% at 3 years, which does not differ from the 26% pre-imatinib rate as shown in the figure. Hence, imatinib started post-induction does not appear to improve survival. Imatinib given with induction may improve the CR rate, but there is insufficient follow up to assess transplant or survival rates. Earlier imatinib may be optimal but overall, our study does not provide evidence yet that imatinib alters the outcome of this disease. Figure Figure Patient characteristics Pre-imatinib (N=267) Post-imatinib (N=153) Gender: Male 150 (56%) 96 (63%) WBC (x 10 ^9/l) (2 unknown): <30 141(53%) 86 (56%) ≥ 30 124 (47%) 67 (44%) Median (range) 26.8 (1.5–438) 21.0 (0.5–491) Age: median (range) 40 (15–60) 42 (16–64) CNS disease (82 unknown) 14 (8%) 4 (3%)

Key Points MRD response has value as a prognostic factor for blinatumomab treatment in R/R B-cell precursor ALL. MRD response was associated with better outcomes in terms of OS and RFS in blinatumomab-treated R/R ALL.

Abstract The International ALL trial, conducted jointly by the MRC in the UK and ECOG in the US (UKALL XII/E2993), recruited 1929 patients between 1993 and 2006. All patients aged 16 to 64 years with newly diagnosed ALL, received the identical two phases of induction therapy. Patients with an HLA-identical sibling were assigned to a sibling allogeneic transplant and those who were Ph-positive could also get an unrelated-donor transplant. Patients who did not have a donor were to be randomized between a single autologous transplant, after conditioning with etoposide/total body irradiation, versus consolidation/maintenance therapy for 2.5 years. Following randomization, but prior to receiving the assigned or randomized therapy, all patients received intensification with 3 cycles of high-dose methotrexate. After excluding patients assigned to an allogeneic transplant, 1028 patients were eligible for randomization but, as in other major transplant studies, only 457 were randomized. The rationale underlying the randomization was based on the fact that protracted consolidation/maintenance therapy in adults, extrapolated from the pediatric experience, had never been prospectively evaluated in the era of intensive chemotherapy. Given that the mortality from autotransplant is not higher than chemotherapy (Goldstone et al. Blood. 2008), it was postulated that if a single autologous transplant is at least as good as standard protracted chemotherapy that may make it the preferable option, except possibly in females in whom fertility may be an issue. The overall survival and the event-free survival were significantly superior among the chemotherapy patients (p = .05) as previously reported (Goldstone et al. Blood. 2008). Because the literature contains reports suggesting a trend in favor of autologous transplantation in some patients with ALL (Dhédiu et al. Leukemia, 2006), an analysis was performed to see if any subgroup of patients could be identified in whom: 1. chemotherapy may not be superior to autologous transplant and 2. autologous transplant may be superior. The table lists a detailed analysis of overall survival looking at various age groups, B- versus T-lineage, the rapidity with which a complete remission was achieved –after phase I or only after phase II of induction. Detailed analysis was also performed by cytogenetics looking at those with standard risk versus those with high risk abnormalities [ t(9;22), t(4;11), t(8;14)] and low hypodiploidy/near triploidy or a complex karyotype (Moorman et al. Blood. 2007)]. In all groups, the chemotherapy group was at least as efficacious as the autograft group, and in some was even significantly superior to autologous transplantation. There is no evidence that other risk factors, such as relapse rate or treatment-related mortality, influenced these overall survival data. In addition, the tests for heterogeneity were not significant across any group. In conclusion, the overall survival was longer in patients randomized to chemotherapy, although the superiority was not statistically significant in most of the groups. There is no clinical indication for autologous transplantation at any age and particularly this should not be considered for patients over age 50, those with high-risk cytogenetics or T-lineage, and late remitters, for whom it might appear most attractive. Overall Survival (OS) at 5 years in 457 Randomized Patients Chemo Auto Subgroups n OS n OS P (log rank) Age (years) < 20 50 58% 43 46% > 0.1 20–29 61 52% 70 43% > 0.1 30–39 46 39% 46 32% > 0.1 40–49 38 31% 35 31% > 0.1 50 + 33 38% 35 31% > 0.1 B-lineage 169 46% 158 35% 0.03 T-lineage 45 54% 54 49% > 0.1 Time to CR phase I 193 48% 190 41% 0.1 phase II 26 36% 29 19% 0.08 Cytogenetics standard-risk 109 51% 122 44% > 0.1 high-risk 29 23% 27 7% 0.02

Abstract Background: Blinatumomab is an investigational bispecific T-cell engager (BiTE®) antibody construct designed to direct cytotoxic T cells to CD19-expressing B cells. In a study in minimal residual disease (MRD)-positive ALL, 80% of pts achieved MRD-negative status after receiving one treatment cycle of blinatumomab (Topp MS, et al. J Clin Oncol. 2011;29:2493-8). For pts with newly diagnosed ALL, persistence of MRD after first-line treatment predicts disease recurrence. However, only limited data are available about the relationship between MRD and outcome in adult pts with r/r ALL. Therefore, the aim of this secondary analysis was to evaluate MRD responses and their relationships to other efficacy indices in adult pts with r/r ALL receiving blinatumomab in this phase 2 study. Methods: Eligibility criteria included adult pts ≥18 years, with Philadelphia chromosome negative B-cell r/r ALL who were primary refractory or refractory to first salvage, had their first relapse within 12 months of first remission or allogeneic hematologic stem cell transplantation (HSCT), or received second or later salvage. Blinatumomab was dosed via continuous IV infusion at 28 μg/d (cycle 1 only: 9 μg/d on days 1-7, 28 μg/d on days 8-28) for up to five cycles (one cycle: 4 weeks on, 2 weeks off). The primary endpoint was complete remission (CR: ≤5% blasts with platelets >100,000/µL, absolute neutrophil count >1000/µL) or CR with partial hematologic recovery (CRh*: platelets >50,000/µL, absolute neutrophil count >500/µL) within the first two treatment cycles. MRD in bone marrow was assessed at a central laboratory using allele-specific real-time quantitative PCR. Two MRD-based exploratory endpoints were analyzed: MRD response (no PCR amplification at a minimum sensitivity of 10-4 or <10-4 leukemic cells by PCR) and complete MRD response (no PCR amplification at a minimum sensitivity of 10-4) within the first two treatment cycles. Results: Of 189 treated pts (median [range] age = 39 [18–79] years), 81 (43%) pts had a CR (n = 63, 33%) or a CRh* (n = 18, 10%) during the first two treatment cycles. In the subgroup of pts with a CR/CRh* and evaluable MRD data (n = 73), 60 (82%) pts had an MRD response. Of those, 51 (70%) pts had a complete MRD response. The majority of those who achieved a CR/CRh* also achieved a complete MRD response regardless of the number of prior lines of salvage therapy (Table 1). Of all treated pts, 64 (34%) pts had prior HSCT. In pts who achieved CR/CRh*, the rate of MRD response was 81% in pts without and 85% in pts with prior HSCT. In pts who achieved CR/CRh*, the median (95% CI) duration of overall survival was 11.4 (8.5, not estimable) months for those with a MRD response and 6.7 (2.0, not estimable) months for those with no MRD response. The median (95% CI) duration of relapse-free survival was 6.9 (5.5, 10.1) months in patients with a MRD response and 2.3 (1.2, not estimable) months in patients with no MRD response. The HSCT realization rate did not differ significantly between pts with CR/CRh* and a MRD response and those with CR/CRh* and no MRD response (31% and 43%, respectively). Seventeen pts classified as nonresponders per protocol had ≤5% blasts and no evidence of disease, but recovery of peripheral counts did not meet criteria for CRh*. Ten of these 17 pts had evaluable MRD assessments; 50% (5/10) had MRD response and 20% (2/10) had complete MRD response. The clinical significance of this finding remains open. Grade ≥3 adverse events regardless of causality and occurring in >10% of all treated pts during treatment until 30 days after treatment were febrile neutropenia (25%), neutropenia (16%), and anemia (14%). Grade 3 cytokine release syndrome (CRS) was reported in three (1.6%) patients. Three (1.6%) patients had grade 4 neurologic events, all resolved. Twenty-one (11%) patients had grade 3 neurologic events, 17 were resolved, with 4 events unresolved at death or unknown. Conclusion: In this largest study to date of adult pts with r/r ALL with PCR-based central assessment of MRD, pts who achieved CR/CRh* during single-agent treatment with blinatumomab had high MRD response rates. The exploratory analyses suggested that within pts with a CR/CRh*, those who did not achieve MRD responses tended to have shorter durations of overall and relapse-free survival. These results are consistent with prior reports highlighting the importance of achieving an MRD response in first-line therapy. Disclosures Goekbuget: Amgen Inc.: Consultancy, Honoraria, Research Funding. Off Label Use: This presentation will discuss the off-label use of blinatumomab, as this agent is not approved for use by the FDA, EMA or any other regulatory authorities. Kantarjian:Amgen Inc.: Research Funding. Brüggemann:Amgen Inc.: Consultancy, Research Funding. Stein:Amgen Inc.: Membership on an entity's Board of Directors or advisory committees. Bargou:Amgen Inc.: Consultancy, Honoraria. Dombret:Amgen Inc.: Research Funding. Heffner:Amgen Inc.: Honoraria, Research Funding; Biotest: Research Funding; Dana Farber CI: Research Funding; Genentech: Research Funding; Gilead: Research Funding; Idera: Research Funding; Janssen: Research Funding; Pfizer: Research Funding; Pharmacyclics: Honoraria, Research Funding; Onyx: Research Funding; Spectrum: Research Funding; Talon Therapeutics: Research Funding. Rigal-Huguet:Amgen, Inc.: Consultancy; Ariad: Consultancy; BMS: Consultancy; Novartis: Consultancy; Pfizer: Consultancy. Litzow:Amgen Inc.: Honoraria, Research Funding. Zugmaier:Amgen Reseach (Munich) GmbH: Employment; Amgen Inc.: Equity Ownership. Jia:Amgen Inc.: Employment, Equity Ownership. Maniar:Amgen Inc.: Employment, Equity Ownership. Huber:Amgen Research (Munich) GmbH: Employment; Amgen Inc.: Equity Ownership. Nagorsen:Amgen Inc.: Employment, Equity Ownership, Related to blinatumomab Patents & Royalties. Topp:Amgen Inc.: Honoraria, Membership on an entity's Board of Directors or advisory committees.

Abstract Abstract 493 The International MRC UKALL XII/ECOG E2993 trial for adults with newly diagnosed acute lymphoblastic leukemia (ALL) recruited 1,914 patients to the main part of the trial from 1995 up to its closure in 2006, of whom 100 were over the age of 55 years (median 57, range 55–65). Beginning in 2003 (MRC) or 2004 (ECOG), patients with Philadelphia chromosome positive (Ph+ve) disease were entered into an Imatinib sub-study. We report here baseline characteristics, treatment course and outcomes, and discuss implications for future management strategies. Direct comparison of the 100 patients over 55 yrs with 1,814 under 55 yrs showed that the groups are comparable for gender, immunophenotype and white cell count but there is an indication that more elderly patients had Ph+ve disease (28% aged ≥55 vs 17% aged <55 of those entered before the start of the Imatinib trial; p=0.02). All patients in this trial received a 2 stage induction regimen, consisting of Daunorubicin, Vincristine, Asparaginase and Steroid followed by Cyclophosphamide, Cytarabine, 6-Mercaptopurine and Methotrexate. CNS prophylaxis with IT Methotrexate and Cytarabine was given during both phases. There was a randomisation to autograft or chemotherapy, but only a small number of patients in this age group were randomised (13 autograft and 13 consolidation chemotherapy). Outcomes Complete remission (CR) rate, event-free survival (EFS) and overall survival (OS) were all worse in the over 55 age group, and even after achieving CR, the 5-year OS rate was reduced. There were more infections in phase I induction (67% vs 45%, p<0.0001) and more deaths during induction chemotherapy (18% vs 4% p<0.0001). Excluding those who died in induction, 47% had drug dose reductions in phase I or phase II vs 27% <55 yrs (P=0.0006). Of these, Asparaginase was the most common in those aged ≥55 years, usually due to hepatotoxicity. Age p-value <55 vs ≥55 <55 ≥55 Number 1814 100 CR No v Yes p<0.0001 No 131 (7%) 27 (27%) No (died in induction) 70 (4%) 18 (18%) No (but survived induction) 61 (3%) 9 (9%) Yes 1641 (90%) 70 (70%) Unknown 42 (2%) 3 (3%) Deaths 1112/1814 (61%) 78/100 (78%) Relapses 750/1683 (45%) 36/73 (49%) Overall survival at 5 years (95% CI) 41% (38–43%) 21% (12–29%) p<0.0001 Event free survival at 5 years (95% CI) 37% (34–39%) 19% (10–27%) p<0.0001 Relapse free survival at 5 years (95% CI) 50% (48–53%) 38% (25–52%) p=0.08 Overall survival at 5 years (95% CI) in those who achieved CR 44% (41–46%) 30% (18–41%) p=0.03 In those patients aged ≥55 years, baseline factors causing a significantly worse 5-yr EFS were Ph-positivity (0% vs 23%, p=0.005), unfavourable vs standard cytogenetic risk (7% vs 26%, p=0.02) and a presenting WCC >50 × 109/l (0% vs 25% for WCC between 10 and 49.9 × 109/l and 23% for WCC <10 × 109/l, p=0.003). Infection during induction chemotherapy predicted for worse EFS; this was especially significant in those who had infection in both phases of induction (6% vs 38%, p=0.007). In those patients who received chemotherapy and were not transplanted, the differences in outcome were smaller: 5-yr OS 25% in ≥55 years vs 38% in <55 years (p=0.06), 5-yr EFS 22% vs 32% (p>0.1). Conclusion Older adults fared significantly worse than younger adults both in terms of achieving an initial CR and long-term survival. This difference cannot be explained solely by a difference in disease characteristics, and the marked increase in infection and deaths during induction reflect the inability of many older patients to tolerate the intensive level of treatment. This is also supported by the large numbers of drug omissions or dose reductions seen. Our data show that this inability to tolerate induction chemotherapy is a major contributor to the poor outcomes seen in this age group. The less marked differences between age groups when transplant patients are excluded, indicates the significant mortality associated with these procedures in older patients. Alternative approaches to consider in this group include less intensive induction with a steroid and vinca alkaloid combination, in conjunction with targeted therapies (eg Rituximab in B-lineage CD20+ disease, Imatinib Mesylate in Ph+ disease). Even amongst those patients who do achieve CR however, the long-term outcome is worse. Reduced intensity allografts may play a role in carefully selected patients in this age group, and the emerging use of MRD monitoring may also assist in selecting patients for more or less intensive approaches. Disclosures: McMillan: EUSA: Honoraria. Goldstone: Roche: Honoraria, Speakers Bureau.

Abstract This study was coordinated by the ECOG-ACRIN Cancer Research Group (Robert L. Comis, MD and Mitchell D. Schnall, MD, PhD, Group Co-Chairs) and the Medical Research Counsel, United Kingdom, and supported in part by Public Health Service Grants CA180820, CA180794, CA180790, CA189859, CA180853, CA180791, and from the National Cancer Institute, National Institutes of Health and the Department of Health and Human Services. Its content is solely the responsibility of the authors and does not necessarily represent the official views of the National Cancer Institute. Background: Late relapse in acute leukemia is considered a relatively rare event. Patients with acute myeloid leukemia (AML) are often considered cured of the disease at 3 years, but information regarding adult acute lymphoblastic leukemia (ALL) patients is scarce. Data are presented from one of the largest prospective adult ALL studies, the MRC UKALLXII/ECOG E2993, to evaluate the rate and characteristics of late relapse in ALL. For this purpose, late relapse was defined, arbitrarily, as relapse 3 years post achievement of complete remission (CR) and very late relapse was defined as relapse > 5 years from CR. Methods: The UKALLXII/ECOG E2993 was an international ALL trial conducted jointly by the MRC in the United Kingdom and ECOG in the United States. All patients received identical induction therapy, followed by central nervous system prophylaxis. Patients with a sibling donor (or a matched unrelated donor in Philadelophia-chromosome-positive ALL) were assigned to receive an allogeneic hematopoietic stem cell transplant (HSCT); all others were randomized to undergo an autologous transplant or protracted standard consolidation/ maintenance therapy. The study accrued 2109 patients from 1993 to 2008. Following relapse, patients were followed for survival. For this report only patients registered before the tyrosine kinase inhibitors era are included in the analysis. Results: 1518 study patients were eligible for this analysis, 1208 (79.6%) Philadelphia-chromosome negative (Ph-neg) and 267 (17.5%) Philadelphia-chromosome positive (Ph-pos). 1381 (91%) of the patients achieved CR; 93% of the Ph-neg and 82% of the Ph-pos. 572 patients (37.7%) underwent allogeneic HSCT. The median duration of follow-up of patients who achieved CR was 10 years. Among the 1381 patients who achieved CR, 626 (45.3%) had a documented relapse; 566 (90.4%) relapsed within 3 years of CR and 60 (9.6%) relapsed beyond 3 years ('late relapse') (Figure 1). Among these 60 patients, 18(2.9%) relapsed after 5 years ('very late relapse'). Table. Patients n CR All relapses Relapses< 3 years Relapses≥ 3 years Relapses≥ 5 years All patients 1518 1381 (91%) 626 (45.3%) 566 (90.4%) 60 (9.6%) 18 (2.9%) Ph-neg 1208 (79.6%) 1123 (93%) 485 (40.1%) 429 (88.5%) 56 (11.5%) 17 (3.5%) Ph-pos 268 (17.5%) 219 (82%) 124 (56.6%) 122 (98.4%) 2 (1.6%) 1 (0.8%) Relapse beyond 3 years occurred in 4.3% of all who achieved CR, in 5% of Ph-neg and 0.01% of Ph-pos patients. Among the 60 late relapses, the median time to relapse was 46 months. 61.7% of the late-relapse patients were males, median age was 32 years, 88.3% were B-lineage ALL and the median white cell count at diagnosis was 6000/ul. 56.7% were in cytogenetic standard risk, 8.3% at high risk and the data of 35% are unknown. The median survival for the late relapse patients was longer than for those who relapsed within 3 years. The overall survival (OS) of the 56 Ph-neg patients who relapsed beyond 3 years is shown in Fig 2. Table.Relapse > 3 yearsRelapse > 3 yearsMedian survival from relapse (months)5.411.23-year OS from relapse6.5%29%5-year OS from relapse5.6%19% Conclusions: Late relapses in adults with Ph-neg ALL are not uncommon. About 10% of relapses occur beyond 3 years and 4.3% of all ALL patients who achieved a CR can expect to have a late relapse. These data are in contrast to AML where only 1% of patients relapse beyond 3 years (Watts JM et al, 2014). Most of the late relapse patients were at standard risk and appeared to have a relatively favorable outcome post relapse. Patients with ALL, particularly those who are Ph-neg, cannot be considered as cured at 3 years and need to be closely followed. Figure 1. Time to relapse of Ph-pos and Ph-neg ALL Figure 1. Time to relapse of Ph-pos and Ph-neg ALL Figure 2. Survival from relapse for Ph-neg patients who relapsed after 3 years from CR. Figure 2. Survival from relapse for Ph-neg patients who relapsed after 3 years from CR. Disclosures Rowe: Amgen: Consultancy; BioSight Ltd.: Consultancy, Membership on an entity's Board of Directors or advisory committees; BioLineRx Ltd.: Consultancy. Douer:Gilead: Consultancy.

Abstract Abstract 524 The International UKALLXII/E2993 trial enrolled 2091 pts with newly diagnosed adult ALL between 1993 and 2006. Patients received 2 months of combination induction chemotherapy followed by an intensification course of high dose methotrexate and L-asparaginase after which pts were randomized to autologous hematopoietic stem cell transplant (HSCT) or consolidation and maintenance chemotherapy. Patients <55 years of age with a matched sibling donor were assigned myeloablative allogeneic HSCT (Goldstone, et al, Blood 2008; 111:1827). Here we report a detailed analysis of 1,229 pts from this trial with B-ALL, excluding Philadelphia-chromosome-positive patients. The median age was 30 years (range 14–65) and 59% were male. The median WBC was 9.2×109/L (range 0.1–930) and 73% of pts had a WBC <30 × 109/L. CNS involvement was present in 4% of pts at diagnosis. Comprehensive centralized immunophenotyping was performed in 372 of the 409 (91%) ECOG pts enrolled and initial analysis demonstrated pro-B/pre-pre-B in 17%, early pre-B in 52%, pre-B in 14%, either early pre-B or pre-B in 6%, mature B in 2% and B-lineage, not otherwise specified, in 9%. Outcomes were similar between patients with immunophenotyping data and those without. The complete remission (CR) rate was 93% and there were 4% induction deaths. The overall survival (OS), event-free survival (EFS), relapse risk (RR) and non-relapse mortality (NRM) at 5 years for the overall group is shown in the table. There were no significant differences in CR rate, OS, EFS, RR or NRM for the immunophenotypic subgroups. There was better OS and EFS with less relapse and similar risk of NRM for pts randomized to chemotherapy as compared with autologous HSCT (Figure 1). In the matched sibling donor-no donor comparison, OS and EFS were improved, RR was less and NRM was higher in the donor group (Figure 2). Cytogenetic analysis confirmed that patients with t(4;11) (n=77, 8% total), t(8;14) (n=19, 2% total), a complex karyotype (≥5 abnormalities in the absence of an established chromosomal abnormality) (n=38, 5% total), or low hypoploidy/near triploidy (n=41, 5% total) had an inferior OS and patients with high hyperdiploidy had a superior OS when compared to other patients. In conclusion, this is the largest series of B-ALL in uniformly treated adults ever reported and confirms the superior outcome of patients randomized to chemotherapy as compared with autologous HSCT and shows that patients with a matched sibling donor have an improved survival over patients without a donor. No difference in CR rates or outcome was noted for patients with different immunophenotypic subtypes of B-ALL. Future improvements in outcome of pts with B-ALL will rely on the addition of new agents such as B cell monoclonal antibodies and improvements in allogeneic HCT.Table.Outcomes at 5 years of follow-upnCR rate (%)OSEFSRRNRMOverall12299342375021Pro-B/pre-pre-B639236345421Early pre-B/pre-B2689340345421Age ≤ 35 years746 (61%)9653454516Chi square p<0.0001<0.0001<0.0001<0.0001<0.0001Age >35 years483 (39%)8932265930Randomized to autologous HSCT15735316610Log rank p0.030.010.01NSRandomized to chemotherapy1694742558Matched sib donor34452483032Chi square p0.050.03<0.001<0.001No Donor47445415510Values are % except n and p values. CR=complete remission, OS=overall survival, EFS=event-free survival, RR=relapse risk, NRM=non-relapse mortality NS=not significant. The p values represent the difference between age groups for the first comparison, randomized to autologous HSCT versus chemotherapy for the second comparison and between matched sibling donor and no donor for the third comparison. Overall survival by randomized allocation at 10 years Overall survival by donor availability at 10 years Disclosures: No relevant conflicts of interest to declare.