Prevalence and Prognostic Impact of KIT Mutations in Acute Myeloid Leukaemia with Inv(16). A Retrospective Study.

Introduction Several studies have recently pointed out the adverse impact of KIT mutations (mutKIT) on relapse incidence (RI) and overall survival (OS) in AML pts with t(8;21). By contrast, the prognostic significance of mutKIT in pts with inv(16) remains unclear. Purpose of this study is to evaluate the prevalence and the prognostic impact of mutKIT in inv(16)(p13q22).

Patients and Methods Fifty adults with inv(16) AML at diagnosis (median age 46.6 yrs, range: 17–88; M/F: 30 /20), were centrally analyzed for mutKIT in exon 2, 8, 10, 11 and 17. Mutations were detected using sequencing and other sensitive assays such as ARMS (amplification refractory mutation system) PCR for D816Y and D816H and enzymatic digestion with HINFI for D816V and with Tsp509I for N822K.

Results Data showed a prevalence of KIT mutation of 34% (17/50 pts). Among the mutKIT cases, we detected mutations in exon 17 (n=12), exon 8 (n= 4) and exon 10 (n=1). There was no difference between the mutKIT vs the unmutated (KIT-) patients in the median of WBC count at presentation (WBC 13.9 x10⁹/L, range 4.4 to 277.5 vs 19.4 x10⁹/L, range 2.5 to 130; Mann-Whitney U test: p = 0.649). Of the 42 patients (age < 60 years) who received intensive chemotherapy, 13 resulted mutKIT upon mutational screening. Complete remission (CR) was achieved in 13/13 (100%) mutKIT vs 27/29 (93%) KIT- patients (Fisher’s exact test: p > 0.999). At a median follow-up of 26 months (range: 2–144), 9/13 (69%) mutKIT and 8/27 (29%)KIT- pts relapsed;the Kaplan-Meier plots revealed KIT mutations to be a significant factor adversely affecting RI (log-rank test: p = 0.017) but not OS (61% in mutKIT vs 75% in KIT-;log-rank test: p = 0.331).

Conclusion KIT mutations are associated with a greater probability of relapse following CR, without affecting OS, in AML pts with inv(16) aged <60 years.