LETTERS TO THE EDITOR GRAALL 2003 and 2005 trials showed that treatment Unique clinico-biological, genetic and prognostic intensification with allogeneic hematopoietic stem cell features of adult early T-cell precursor acute transplantation (HSCT) in ETP-ALL with early treatment lymphoblastic leukemia resistance could improve survival.12 Here we retrospectively analyzed the frequency, clini- Early T-cell precursor (ETP) acute lymphoblastic co-biological and prognostic features of adult ETP-ALL leukemia (ALL), was first identified within cases of child- vs. other T-ALL cases in a series of 185 adults with T-ALL hood T-ALL based on its unique immunophenotypic and treated within two consecutive minimal residual disease- genetic features of limited (early) T-cell differentiation oriented trials by the Programa Español de Tratamientos en associated with (some) myeloid and stem cell features.1 Hematología (PETHEMA): ALL-HR-2003 (NCT00853008) Thus ETP-ALL blasts express CD7, dim CD5 (<75% pos- and ALL-HR-11 (NCT01540812), the latter still ongo- itive cells), in the absence of CD1a and CD8, and positiv- ity for ≥1 myeloid/stem cell related markers (i.e., CD34, ing). All 185 patients were diagnosed with T-ALL using the CD13 or CD33).1,2 In turn, ETP-ALL frequently shows WHO criteria. The treatment protocol schedules have myeloid-associated gene alterations such as FLT3, been described previously elsewhere.13,14 The patients’ NRAS/KRAS, DNMT3A, IDH1 and IDH2 mutations,3,4 characteristics at diagnosis and at follow-up are summa- with lower frequencies of other T-ALL-associated muta- rized in Table 1. The immunological T-ALL subtype was tions (e.g., NOTCH1 and CDKN2A/B gene mutations).5,6 defined according to the European Group for the The World Health Organization (WHO) 2016 classifica- Immunological Characterization of Leukemias (EGIL) cri- tion of ALL included ETP-ALL for the first time, as a pro- teria after centralized review of immunophenotypic visional entity,7 but it failed to establish robust diagnostic reports. In turn, the criteria proposed by Zuurbier et al.2 criteria. Thus, after the first immunophenotypic charac- were used to define ETP-ALL. The combination of mark- terization of ETP-ALL by Coustan-Smith et al.1 the pro- ers used (<5% CD1a, CD8 and CD4; >25% CD34 and/or posed criteria did not allow identification of all ETP-ALL CD33/CD13), resembles that proposed by Coustan- cases as detected by gene expression profiling.2 In addi- Smith et al., while dim CD5 expression (<75% positive tion, the “partial CD5 expression” criterion had a nega- cells) was not considered. The inclusion of negativity for tive impact on the reproducibility of ETP-ALL diagnoses CD4 instead of dim CD5 expression as an immunophe- because of the lack of standardization of the method used notypic criterion, allows identification of most ETP-ALL for its assessment. Because of this, Zuubier et al. pro- cases identified by gene expression profiling (increased posed refined immunophenotypic criteria by excluding sensitivity of immunophenotyping to detect ETP-ALL CD5 expression while adding negativity for CD4.2 cases).2 Clinical data were obtained in accordance with From the clinical point of view early studies based on the principles of the Declaration of Helsinki and Spanish limited numbers of pediatric patients indicated that ETP- legislation, after written informed consent had been pro- ALL was associated with a very poor outcome.1,8,9 More vided by each patient. The study was approved by the recent data, based on larger series of children treated Institutional Review Board of the Hospital Germans Trias with more intensive therapy, showed no significant dif- i Pujol (Badalona, Spain). ferences in outcome for ETP-ALL vs. other T-ALL cases.10 Comparisons between ETP-ALL and other T-ALL cases In contrast, limited data have been reported for adult were performed with the χ2 test, Fisher exact test, and the ETP-ALL, with conflicting results.11,12 In one study, adult median test, as appropriate. Event-free survival and over- ETP-ALL was associated with a worse prognosis follow- all survival curves were plotted using the Kaplan-Meier ing different frontline chemotherapy schedules.11 The method and compared by the log-rank test. A secondary A B P=0.037 P=0.015 Figure 1. Impact of allogeneic hematopoietic stem cell transplantation on overall survival of patients with or without early T-cell precursor acute lymphoblastic leukemia. (A) Overall survival of adults with early T-cell precursor acute lymphoblastic leukemia (ETP-ALL) vs. other non-ETP T-ALL adult patients censored at transplantation; the survival probability, with 95% confidence interval (95% CI) at 4 years was 36% (95% CI: 13-59%) for the ETP-ALL group and 49% (95% CI: 39-59%) for the other non-ETP patients. (B) Overall survival of ETP and non-ETP T-ALL patients not censored at transplantation. The survival probability at 4 years was 33% (95% CI: 16-50%) for ETP-ALL patients vs. 51% (95% CI: 42-60%) for the non-ETP T-ALL group. haematologica 2020; 105:e294 LETTERS TO THE EDITOR Table 1. Clinico-biological and prognostic characteristics together with response to treatment of early T-cell precursor acute lymphoblastic leukemia vs. other types of T-cell acute lymphoblastic leukemia. Wholes series ETP-ALL Other non-ETP T-ALL P (n=185) (n=34) (n=133) Age (years)* 33.5 (12) 39 (12) 33 (12) 0.01 Female/male ratio 49/136 13/21 30/103 0.06 Lymph node enlargement 65/163 (40%) 23/29 (79%) 66/118 (56%) 0.02 Splenomegaly 61/178 (34%) 8/31 (26%) 49/130 (38%) 0.21 Hepatomegaly 40/175 (23%) 7/31 (23%) 30/127 (24%) 0.90 Mediastinal mass 86/182 (47%) 15 (44%) 65/131 (50%) 0.57 WBC count (x109/L)* 94.3 (121.0) 72.2 (155.1) 96.6 (111.7) 0.004 CNS involvement 18/178 (10%) 6/33 (18%) 12/130 (9%) 0.21 Complex karyotype** 9/141 (6%) 3/22 (14%) 6/104 (6%) 0.19 Del (6q) 10/140 (7%) 1/21 (5%) 9/104 (9%) 0.47 CDKN2A/B gene deletion 31/53 (58%) 1/11 (9%) 29/40 (73%) <0.001 TCRG gene deletion 24/31 (77%) 3/8 (37%) 19/20 (95%) 0.003 Slow response at day +14 82/172 (48%) 27/33 (82%) 46/123 (37%) <0.001 1 induction cycle to CR 153/167 (92%) 19/26 (73%) 118/125 (94%) 0.003 2 induction cycles to CR 14/167 (8%) 7/26 (27%) 7/125 (6%) CR 167/185 (90%) 26 (77%) 125/133 (94%) 0.005 MRD day +35 <0.1% 106/141 (75%) 7/20 (35%) 90/110 (82%) <0.001 MRD day +35 <0.01% 74/132 (44%) 3/20 (15%) 65/104 (63%) <0.001 Chemotherapy 86/121 (71%) 6/20 (30%) 72/91 (79%) <0.001 Allogeneic HSCT 35/121 (29%) 14/20 (70%) 19/91 (21%) Results expressed as number of cases (percentage) or *as a mean (standard deviation). **More than five cytogenetic abnormalities. Minimal residual disease values were considered only for those patients who reached complete remission. Statistically significant values are shown in bold. ETP: early T-cell precursor; ALL: acute lymphoblastic leukemia; WBC: white blood cell; CNS: central nervous system; CR: complete remission; MRD: minimal residual disease; HSCT: hematopoietic stem cell transplantation. analysis of overall survival was performed, with trans- genetic markers for the diagnosis of ETP-ALL. However, planted patients censored at the time of allogeneic HSCT. some discordance between immunophenotypic and Cumulative incidence of relapse and non-relapse-related genetic results was observed, which might be due to the mortality were analyzed as competing events with the limited sensitivity of current immunophenotypic criteria, Gray test. A Cox proportional hazard regression model highlighting the need for more precise and robust criteria was used to identify predictive factors for event-free and and standardized methods for the diagnosis of ETP-ALL. overall survival, whereas multivariate analysis for cumu- No significant differences in complete response, overall lative incidence of relapse was performed with the Fine survival, event-free survival and cumulative incidence of and Gray model. Statistical significance was set at P-val- relapse rates were observed between ETP-ALL patients ues <0.05. enrolled in the two treatment protocols (data not shown). Full immunophenotypic data according to the EGIL cri- This allowed a combined evaluation of the data from teria were available for 167/185 T-ALL patients; 34/167 both PETHEMA trials. ETP-ALL patients showed signifi- (20%) T-ALL cases met criteria for ETP-ALL as defined by cantly poorer response to induction therapy compared to both Zuurbier et al. and the WHO.7 This frequency is sim- other T-ALL patients (Table 1). Thus, ETP-ALL patients ilar to that observed in previously published cohorts of had poorer bone marrow response (<10% blasts) on day adults with T-ALL11,12 in which the phenotypic criteria +14 compared to other T-ALL cases (18% vs. 63%, applied in early pediatric studies to define ETP-ALL were P<0.001); half of ETP-ALL cases required second induc- used.1 Significant differences were observed when com- tion treatment (vs. 10% of the remaining T-ALL cases, paring ETP-ALL and non-ETP-ALL cases at diagnosis P<0.001) and 23% of them did not attain a complete (Table 1). Patients with ETP traits were older [mean ± response (vs. only 6% of other T-ALL cases, P=0.005). standard deviation (SD): 39±12 years vs. 33±12 years, Minimal residual disease data were available for 132/167 P=0.01], more frequently had lymph node enlargement patients who reached a complete resposne after one or (79% vs. 56%, P=0.02), had lower white blood cell two induction cycles. Two-thirds (65%) of ETP-ALL counts (mean±SD: 72.2±155.1x109/L vs. 96.6±111.7 cases showed minimal residual disease levels ≥0.1% (vs. x109/L, P=0.004), and showed a slightly different female 18% of non-ETP-ALL cases, P<0.001), the percentage to male ratio (13/21 vs. 30/103, P=0.06), similarly to what increasing to 85% (vs. 37%, P<0.001) at a cut-off level of has been shown for the GRAALL cohort.12 In addition, 0.01%. Consequently, as indicated per protocol, more our ETP-ALL cases frequently showed absence of ETP-ALL patients underwent allogeneic HSCT (70% vs. CDKN2A/B (P<0.001) and TCRG (P=0.003) gene dele- 21%, P<0.001). Despite treatment intensification with tions. These results are in line with those previously allogeneic HSCT, ETP-ALL patients did not attain a sig- reported in the literature6,14,16 and support the use of both nificant improvement in the probability of overall sur- haematologica 2020; 105:e295 LETTERS TO THE EDITOR vival (Figure 1A, B). In fact, differences in overall and Madrid; 4Clinical Hematology Service, Hospital Universitari de la Vall event-free survival between ETP-ALL and other non-ETP d'Hebron, Barcelona; 5Clinical Hematology Service, Hospital General T-ALL patients were mostly due to the greater rate of fail- de Alicante, Alicante; 6Clinical Hematology Service, Hospital Josep ure to induction therapy, with a minimal contribution of Trueta-ICO, Girona; 7Clinical Hematology Service, Hospital Vírgen de the higher (non-statistically significant) cumulative inci- la Victoria, Málaga; 8Clinical Hematology Service, Hospital dence of relapse observed among ETP-ALL patients vs. Universitario Central de Asturias, Oviedo; 9Clinical Hematology other T-ALL cases (Online Supplementary Figure S1). Service, Hospital de la Santa Creu i Sant Pau, Barcelona; 10Clinical However, it should be noted that the overall survival rate Hematology Service, Hospital Vírgen del Rocío, Sevilla; 11Clinical of adult T-ALL patients from the PETHEMA cohort who Hematology Service, Hospital Clínic de Barcelona, Barcelona; 12Clinical underwent allogeneic HSCT was lower than that Hematology Service, Hospital Duran i Reynals-ICO, Hospitalet del observed in other studies.12,13 Thus, the improvement of Llobregat; 13Clinical Hematology Service, Hospital Universitario de non-transplant-related mortality in transplanted patients Donostia, Donostia; 14Clinical Hematology Service, Hospital Son might have a positive impact on survival of Llàtzer, Palma de Mallorca; 15Clinical Hematology Service, Hospital ETP-ALL patients. Multivariate analyses showed that Clínico de Valencia, Valencia; 16Clinical Hematology Service, Hospital ETP-ALL was an independent adverse predictor for both Marqués de Valdecilla, Santander; 17Clinical Hematology Service, overall survival and event-free survival [hazard ratio of Hospital Mútua de Terrassa, Terrassa; 18Clinical Hematology Service, 2.14 (95% confidence interval: 1.29- 3.53), P=0.003 and Hospital 12 de Octubre, Madrid; 19Clinical Hematology Service, 1.91 (1.18-3.11), P=0.009, respectively] together with a Hospital Morales Meseguer, Murcia; 20Clinical Hematology Service, high white blood cell count (Online Supplementary Table Hospital Gregorio Marañón, Madrid; 21Clinical Hematology Service, S1). Hospital Son Espases, Palma de Mallorca; 22Clinical Hematology In summary, here we confirmed the previously report- Service, Hospital Joan XXIII, Tarragona; 23Clinical Hematology ed frequency and clinico-biological features of adult ETP- Service, Hospital Arnau de Vilanova, Lleida and 24Centro de ALL and showed that adult ETP-ALL patients should be Investigación del Cáncer (IBMCC-CSIC/USAL), Hospital Clínico considered as a group with a worse prognosis. The poor- Universitario de Salamanca, Instituto Bio-Sanitario de Salamanca, er outcome of ETP-ALL patients in our study was due to CIBERONC Salamanca, Spain a lower response to induction therapy and not to an Acknowledgments: we would like to thank Rosa Coll, Rodrigo increased relapse rate, which highlights the need to Martino, Raimundo García Boyero, Jesús Mª Hernández Rivas, investigate the potential utility of alternative induction Pilar Herrera, Juan Bergua, Mª Jesús Peñarrubia, Eloy del Potro, therapy for these patients. The use of acute myeloid Magdalena Sánchez, Beatriz Soria, Aurelio López Martínez, Mª José leukemia-oriented chemotherapy, together with intensi- Sánchez Sánchez, Pilar Bravo, Pilar Vivancos, Alfons Serrano, José fication of chemotherapy regimens, has been effective in Santiago Bermón, Maria Lourdes Amador Barciela and Matxalen clearing disease in pediatric ETP-ALL cases refractory to Olivares Salaverri for providing retrospective clinical data for this study. initial induction chemotherapy.17 A similar strategy could Funding: this project was supported by the Asociación Española be applied to adult ETP-ALL patients. Based on these Contra el Cáncer (project ref: GC16173697BIGA), PI14/01971 FIS, findings, and given the poor response attained in adults Instituto Carlos III, CERCA Program/Generalitat de Catalunya, with the conventional induction regimen, it makes sense 2014-SGR225 (GRE), Obra Social “La Caixa” . This work was also to explore the potential benefit of the FLAG-IDA regimen partially supported by FEDER funds from the ISCIII (idarubicin; fludarabine; ARA-C and granulocyte colony- (PT13/0010/0026, CIBERONC (CB16/12/00284 and stimulating factor), a more myeloid-oriented chemother- CB16/12/00400), Madrid, Spain). P. Barba was supported by the apy schedule, as front-line induction treatment together Instituto de Salud Carlos III FIS16/01433 and PERIS 2018-2020 with allogeneic HSCT after standard consolidation. In from Generalitat de Catalunya (BDNS357800) grants. addition, new therapies targeting specific genes altered in ETP-ALL patients, such as FLT3 inhibitors, have emerged Correspondence: as novel alternative treatment strategies. 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