PF574 TARGETED ULTRA‐DEEP NGS ASSESSMENT OF TP53 MUTATIONS IN MULTIPLE MYELOMA FROM WHOLE BONE MARROW

Abstract

Background:Among the most important prognostic genetic aberrations in multiple myeloma (MM) are del(17p) and/or TP53 mutations. The use of the whole bone marrow (BM), when sorted MM cells are not available, may greatly simplify the NGS assessment in MM patients for clinical decisions.Aims:Therefore, the objective of our study was to assess applicability of ultra‐deep targeted NGS for analysis of TP53 mutations and other commonly mutated genes NRAS, KRAS and BRAF using the whole BM samples and compare it to results from MM sorted cells.Methods:BM samples were obtained from MM patients (n = 35, 12 M/23 F). The gDNA was isolated from whole BM (infiltration of plasma cells: median 16.4%, min‐max 1.2 ‐ 65.6%) and paired sorted MM cells. The full coding sequence and 5́and 3́UTR regions of the TP53 gene and hotspots of NRAS, KRAS and BRAF were analysed using ultra‐deep NGS with the MiSeq system (Illumina). The cut‐off for mutation detection was 1% variant allele frequency (VAF), the binomial distribution equation was used to determine a minimum number of mutant alleles.Results:Of MM patients, 22.9% (8/35) harboured mutations in TP53 gene, 20.0% (7/35) KRAS, 14.3% (5/35) NRAS and 8.6% (3/35) BRAF in the whole BM. In all patients, the VAF was in accordance with plasma cells infiltration in BM. Regarding TP53, five patients carried only TP53 mutations, two had a co‐occurrence of TP53 mutations and del(17p) and one had TP53 mutation together with 17chr trisomy as assessed by FISH. In TP53, all of the mutations except one case were observed with low frequency (VAF 2–9%). In cases when paired sorted sample was available, the mutations found in the whole BM were confirmed in sorted MM cells.Summary/Conclusion:Our results demonstrate the applicability of ultra‐deep targeted NGS in assessment of TP53 mutations in the whole BM samples in MM when sorted population is not available. Moreover, our data highlights the importance of assessment of TP53 mutations in MM patients, as they may occur regardless of del(17p). Our approach may simplify the assessment of mutational landscape in MM patients and thus impacts clinical decision making.Grant support: MZ ČR VES16–32339A, IGA UP_2019_014, MH CZ–DRO (FNOL, 00098892), NV18–03‐00500