Immunoglobulin heavy chain variable region gene and prediction of time to first treatment in patients with chronic lymphocytic leukemia: Mutational load or mutational status? Analysis of 1003 cases
Authors: Fortunato Morabito, Tait D Shanafelt, Massimo Gentile, Gianluigi Reda, Francesca Romana Mauro, Davide Rossi, Nicola Di Renzo, Stefano Molica, Francesco Angrilli, Annalisa Chiarenza, Giovanna Cutrona, Kari G. Chaffee, Sameer A. Parikh, Giovanni Tripepi, Graziella D'Arrigo, Ernesto Vigna, Anna Grazia Recchia, Agostino Cortelezzi, Gianluca Gaidano, Francesco Di Raimondo, Franco Fais, Robin Foà, Antonino Neri, Manlio Ferrarini
Journal: American Journal of Hematology (2018)

The mutation status of the immunoglobulin heavy chain variable region gene (IGHV) is a well-recognized prognostic indicator in patients with chronic lymphocytic leukemia (CLL). The occurrence of IGHV somatic hypermutations (SHM) in CLL cells1 and the predictive value of its presence or absence have been recognized in patients with CLL for roughly 20 years.2, 3 The cut-off value of a 2% deviation from (or ≤ 98% identity with) the corresponding IGHV germline sequence has been used in the initial studies to distinguish "mutated" (M-CLL) from "unmutated" (UM-CLL) cases. Based on this cut-off value, it was determined that unmutated cases had a significantly shorter time to first treatment (TTFT) and outcome.2-4 This cut-off value was selected based on the consideration that differences of IGHV genes from the germline of up to 2% might have been related also to allele polymorphisms within the immunoglobulin loci.5 These somewhat conservative parameters were also suggested by the relative scanty number of sequence data available at that time. The frequency of IGHV gene polymorphisms was reported to be 0.0005% by a subsequent study suggesting that a cut-off value of 99.99% homology to the germline would be sufficient to distinguish truly unmutated from mutated cases.6 Some of the subsequent studies indicated that a 2% cut-off value was adequate to distinguish 2 subgroups of patients with a different prognostic expectation7-9 while others, virtually in equal numbers, proposed different cut-off values.10-12 Despite these discrepancies, the 2% cut-off value is generally adopted in the current clinical practice. Recently, Jain et al.13 demonstrated in patients treated with the fludarabine, cyclophosphamide, and rituximab regimen that their subsequent course and survival was greatly influenced by the amount of mutations present in the IGHV gene segment. Thus, the higher levels of mutation corresponded to a better outcome, pointing to the potential prognostic relevance of the percentage of IGHV gene mutation as a continuous rather than a dichotomized variable.13 The particular study design adopted by Jain et al. raises the question of whether their criteria for mutation evaluation have a universal value or apply only to patients treated with that particular protocol, as pointed out by Gocke and Richardson in a recent commentary.14 We assessed the prognostic significance of the extent of SHM on the TTFT in a large cohort of 467 newly diagnosed Binet stage A patients from several Italian institutions who were prospectively enrolled in the O-CLL protocol (training cohort, median follow-up 84 months; clinicaltrial.gov identifier: 115 NCT00917540). The same analysis was performed on a Mayo Clinic validation cohort of 536 cases (median follow-up of 78 months). Further details and data analyses are described in the Supporting Information Appendix. Among the 141 cases classified as UM-CLL in the O-CLL protocol based on the ≤2% mutation cut-off point, 94 (67%) did not present any mutation (truly unmutated cases), 31(22%) presented a 1% mutation and 16 (11%) presented a 2% mutation (Figure 1A). No significant differences were noted in the TTFT of these 3 groups of patients (Figure 1B). The remaining 326 cases, classified as mutated in the O-CLL protocol, had a more even distribution among the different mutation categories according to criteria similar to those employed by Jain et al. (Figure 1A). However, no significant differences were observed in terms of risk to be treated in the groups of mutated cases stratified according to the extent of SHM (Figure 1C). Similar results were observed in the 536 cases of the Mayo Clinic cohort (Figure 1D-F), which provided a further validation of the O-CLL data. Thus, a ≥ 98% homology between the IGHV genes of CLL clones and their normal counterpart represents a valid discriminant to distinguish groups with a different prognostic likelihood, without a need for a further stratification based upon the extent of IGHV gene mutation. With the aim of further validating this result, a Cox multivariable analysis was performed introducing into the model a minimal number of variables which represented a significant discriminant for TTFT in the Cox univariate analysis—ie, Rai stage (H.R. 2.5, C.I. 2.0-3.2, P < .0001), β2M (H.R. 2.3, C.I. 1.8-2.9, P < .0001)—together with the extent of IGHV mutation leading to the stratification of CLL cases into different groups. This analysis was carried out on the 870 cases in which all the 3 variables were available in both the O-CLL and Mayo Clinic cohorts. Notably, in this minimalistic multivariable model, only cases with a IGHV mutational load of 0%, >0 to <1% and 1 to ≤2% maintained an independent prognostic impact on TTFT, together with β2M and Rai stage (Figure 2), while the remaining patient groups, obtained by stratification according to the extent of SHM, failed to maintain an independent prognostic relevance. The same analysis carried out by a bootstrapping Cox regression model provided similar results (Supporting Information Table S1). In conclusion, this study indicates that a ≤ 2% IGHV gene mutation represents a suitable cut-off level capable of discriminating cases with a different prognosis. Hence, the classic distinction of mutated and unmutated cases may be adequate in the current clinical practice. Furthermore, it appears that CLL cases with values below the set cut-off point truly represent the vast majority of unmutated cases. Finally, stratification methods based upon the extent of the IGHV mutation do not seem [superfluous at least] to add in determining the chance for a given patient to be treated, although it remains to be seen whether such stratification may be needed for a more accurate prognostication in special clinical situations as those reported by Jain et al.13 In addition to the listed Authors, the following Investigators participated in this study: Gianni Quintana, Divisione di Ematologia, Presidio Ospedaliero "A.Perrino", Brindisi; Giovanni Bertoldero, Dipartimento di Oncologia, Ospedale Civile, Noale, Venezia; Paolo Di Tonno, Dipartimento di Ematologia, Venere, Bari; Robin Foà and Francesca R Mauro, Divisione di Ematologia, Università La Sapienza, Roma; Nicola Di Renzo, Unità di Ematologia, Ospedale Vito Fazzi, Lecce; Maria Cristina Cox, Ematologia, A.O. Sant'Andrea, Università La Sapienza, Roma; Stefano Molica, Dipartimento di Oncologia ed Ematologia, Pugliese-Ciaccio Hospital, Catanzaro; Attilio Guarini, Unità di Ematologia e Trapianto di Cellule Staminali, Istituto di Oncologia "Giovanni Paolo II", Bari; Antonio Abbadessa, U.O.C. di Oncoematologia Ospedale "S. Anna e S. Sebastiano", Caserta; Francesco Iuliano, U.O.C. di Oncologia, Ospedale Giannettasio, Rossano Calabro, Cosenza; Omar Racchi, Ospedale Villa Scassi Sampierdarena, Genova; Mauro Spriano, Ematologia, A.O. San Martino, Genova; Felicetto Ferrara, Divisione di Ematologia, Ospedale Cardarelli, Napoli; Monica Crugnola, Ematologia, CTMO, Azienda Ospedaliera Universitaria di Parma; Alessandro Andriani, Dipartimento di Ematologia, Ospedale Nuovo Regina Margherita, Roma; Nicola Cascavilla, Unità di Ematologia e Trapianto di Cellule Staminali, IRCCS Ospedale Casa Sollievo della Sofferenza, San Giovanni Rotondo; Lucia Ciuffreda, Unità di Ematologia, Ospedale San Nicola Pellegrino, Trani; Graziella Pinotti, U.O. Oncologia Medica, Ospedale di Circolo Fondazione Macchi, Varese; Anna Pascarella, Unità Operativa di Ematologia, Ospedale dell'Angelo, Venezia-Mestre; Maria Grazia Lipari, Divisione di Ematologia, Ospedale Policlinico, Palermo, Francesco Merli, Unità Operativa di Ematologia, A.O.S. Maria Nuova, Reggio Emilia; Luca Baldini Istituto di Ricovero e Cura a Carattere Scientifico Cà Granda-Maggiore Policlinico, Milano; Caterina Musolino, Divisione di Ematologia, Università di Messina; Agostino Cortelezzi, Ematologia and CTMO, Foundation IRCCS Ca' Granda Ospedale Maggiore Policlinico, Milano; Francesco Angrilli, Dipartimento di Ematologia, Ospedale Santo Spirito, Pescara; Ugo Consoli, U.O.S. di Emato-Oncologia, Ospedale Garibaldi-Nesima, Catania; Gianluca Festini, Centro di Riferimento Ematologico-Seconda Medicina, Azienda Ospedaliero-Universitaria, Ospedali Riuniti, Trieste; Giuseppe Longo, Unità di Ematologia, Ospedale San Vincenzo, Taormina; Daniele Vallisa and Annalisa Arcari, Unità di Ematologia, Dipartimento di Onco-Ematologia, Guglielmo da Saliceto Hospital, Piacenza; Francesco Di Raimondo and Annalisa Chiarenza, Divisione di Ematologia, Università di Catania Ospedale Ferrarotto, Catania; Iolanda Vincelli, Unità di Ematologia, A.O. of Reggio Calabria; Donato Mannina, Divisione di Ematologia, Ospedale Papardo, Messina, Italy. This work was supported by: Associazione Italiana Ricerca sul Cancro (AIRC) and Fondazione CaRiCal co-financed Multi-Unit Regional Grant 2014 n.16695 (to F.M.) Italian Ministry of Health 5x1000 funds 2014; Gilead Fellowship program 2017 project n 8878 (to G.C.), Italian Ministry of Health 5x1000 funds 2013, Italian Ministry of Health 5x1000 funds 2015 and AIRC IG 15426 (to F.F.). A.G R. was supported by Associazione Italiana contro le Leucemie-Linfomi-Mielomi (AIL) Cosenza - Fondazione Amelia Scorza (FAS). All authors read and approved the final version of the article. Designed the study, analyzed, and interpreted data, and wrote the article: Morabito, Shanafelt, Gentile, Foà, Neri, Gaidano, Fais, Ferrarini Performed statistical analysis: Gentile, Tripepi, D'Arrigo, Chaffee, Morabito Performed central laboratory tests: Cutrona, Recchia, Neri, Fais, Morabito Provided the patients and collected clinical data: article: Reda, Mauro, Rossi, Di Renzo, Angrilli, Angrilli, Angrilli, Di Raimondo, Gaidano, Cortelezzi, Parikh, Vigna The authors declare that they have no conflict of interest with the contents of this article. Appendix S1: Supporting information Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.