AML with Inv(3)(q21q26) or t(3;3)(q21;q26) Are Frequently Accompanied by Mutations in RUNX1 and NRAS and Show a High Incidence of NF1 Deletions: a Study On 40 Cases.

Abstract 273

AML with inv(3)(q21q26) or t(3;3)(q21;q26) have been defined as a distinct entity in the WHO classification in the category of “acute myeloid leukemia with recurrent genetic abnormalities”. Whereas cases with t(8;21)(q22;q22), inv(16)(p13q22/t(16;16)(p13;q22) or t(15;17)(q22;q12) are considered as acute leukemias regardless of the percentage of blasts in the bone marrow, it is not clear whether cases with inv(3)(q21q26)/t(3;3)(q21;q26) should be categorized as such if blast cell count is <20%. To analyze the spectrum of myeloid neoplasms in which inv(3)/t(3;3) occurs, all cases with these abnormalities as diagnosed since 2005 in our laboratory were identified. CML cases showing a t(9;22) and inv(3)/t(3;3) were not included as here CML blast crisis was evident. To further decipher accompanying genetic lesions in AML with inv(3)(q21q26)/t(3;3)(q21;q26) we performed in addition to chromosome banding analyses, FISH for the detection of NF1 deletions and mutation screening of NPM1, MLL (PTD), FLT3 (ITD, TKD), RUNX1, KIT (D816), NRAS (codon12/13/61), CBL (exon8/9 splice mutation), MPL, and JAK2 (V617F, exon12). The study cohort included 20 males and 20 females. Median age was 64.8 years (range: 36.3–91.3), median WBC was 3.9G/l (range: 1.1–75.0G/l) and median platelet count 133G/l (range: 5–799G/l). Based on cytomorphology 23 cases were classified as AML (de novo: 18, t-AML: 2, s-AML: 3 (2 after MPN, 1 after MDS), 15 as MDS and 2 as MPN. 27 showed an inv(3)(q21q26) and 13 a t(3;3)(q21;q26). Additional chromosome aberrations were observed in 23/40 (57.5%) cases (AML: 16/23, 69.6%; MDS 7/17, 41.2%): one, two or more than two additional aberrations in 13, 6 and 4 cases, respectively. Recurrent abnormalities were −7 (n=17), del(5q) (n=4). The following molecular mutations were detected: FLT3-TKD (1/32, 3.1%), NRAS (7/29, 24%), RUNX1 (6/29, 20.7%), CBL exon8/9 splice mutation (n=2/24, 8.3%) and JAK2V617F (2/27, 7.4%). One case each with JAK2V617F was diagnosed with MPN and s-AML after MPN, respectively. No mutations were detected for: NPM1 (0/20), MLL-PTD (0/22), FLT3-ITD (0/35), KIT (0/25), JAK2exon12 (0/13) and MPL (0/13). One copy of the NF1 (neurofibromin 1) gene, which negatively regulates the RAS pathway, was found to be deleted in 4/26 (15.4%) cases using FISH (NF1/MPO probe from Kreatech, Amsterdam, The Netherlands). Overall, 22 molecular alterations were observed in the analyzed genes (15 in AML cases, 7 in MDS/MPN cases). Taking also additional cytogenetic aberrations into account 31/40 patients (20/23 AML, 11/17 MDS/MPN) showed further genetic abnormalities in addition to inv(3)/t(3;3). Survival data were available in 28 cases. No significant differences were observed with respect to overall survival (OS) and event-free survival (EFS) between cases diagnosed as MDS or MPN vs AML. Whereas no impact of additional chromosome aberrations or presence of molecular mutations on OS was observed, a trend for a shorter OS in cases with RUNX1 mutation was found (2 months vs 21.8 months, p=0.07). In addition 17 cases with inv(3)(q21q26)/t(3;3)(q21;q26) and de novo AML were compared to 814 de novo AML without inv(3)(q21q26)/t(3;3)(q21;q26). The median OS for the total cohort was 48.2 months (mo), the median EFS 16.3 mo. Based on cytogenetics cases were assigned into 8 subgroups: 1. t(15;17)(q22;q21), 2. t(8;21)(q22;q22), 3. inv(16)(p13q22)/t(16;16)(p13;q22), 4. 11q23/MLL abnormalities, 5. inv(3)(q21q26)/t(3;3)(q21;q26), 6. normal karyotype, 7. complex karyotype, 8. other abnormalities. Median OS was not reached for groups 1, 2, 3, 4, and 6 and was 23.4 mo, 11.8 mo and 32.2 mo for groups 5, 7, and 8, respectively. OS at 2 yrs was 95.6%, 96.3%, 76.6%, 64.9%, 47.5%, 63.5%, 23.9% and 58.5% for groups 1–8, respectively. The respective data for median EFS were: not reached for groups 1 and 2 and 15.9 mo, 13.5 mo, 6.3 mo, 16.9 mo, 7.5 mo and 12.5 mo for groups 3–8, respectively. In summary, inv(3)/t(3;3) is observed in MDS, MPN, de novo AML, s-AML and t-AML and frequently accompanied by additional cytogenetic or molecular genetic abnormalities. Especially frequent were mutations in RUNX1, NRAS and deletions of NF1. Prognosis of patients with inv(3)/t(3;3) is unfavourable irrespective of the cytomorphological diagnosis. These data suggest to consider cases with inv(3)/t(3;3) as one entity regardless of blast cell count.