TP53 single nucleotide variants (SNV) in patients developing second malignant neoplasms after treatment for childhood acute lymphoblastic leukemia

Introduction: Today more than 80% of the children with acute lymphoblastic leukemia (ALL) can be cured by application of intensive contemporary treatment regimens [1]. The most severe treatment-related late effects in ALL survivors are second malignant neoplasms (SMN): within 15 years off diagnosis, 1.5 to 2.5% of long-term survivors will develop a SMN, one third of which are therapy-related myeloid neoplasms (t-MN). As cure rates of SMN are often dismal, future strategies are urgently needed to elucidate patients' predisposition for SMN development. The most frequently mutated gene in cancer is TP53, which has also been studied in certain hematologic neoplasms including ALL. However, the role of TP53 mutations in the pathobiology of SMN after treatment for ALL is largely unknown. Using targeted sequencing, the present study aimed to detect TP53 SNV in patients who developed a SMN after undergoing treatment for ALL.

Methods: Fourty-nine patients treated in Germany on 7 consecutive ALL-BFM multicenter trials from 1979 to 2005 who developed a SMN and had adequate material available for analysis were identified [2]. With the exception of ALL-BFM 79, treatment was stratified into 3 branches, mainly according to the initial leukemic cell load, adverse genetic aberrations and treatment response. Multiplex PCR based on Ion AmpliSeq™TP53 Panel (Life Technologies, Darmstadt, Germany) was carried out according to the manufacturer's instructions. SPSS (IBM Deutschland GmbH, Ehningen, Germany) was used for computerized calculations.

Results: Targeted sequencing of TP53 revealed a frequency of 74 exonic SNV in 40/49 analyzed patients. Within the coding region two concurrent variants were found in 23/49 patients. The majority of these alterations (93%) were missense mutations. The most frequent was p.Pro72Arg (rs1042522; G/C 51%; C/C 45%) located in the proline-rich domain. Less frequently p.Asn235Ser (rs144340710; T/C 2%), a rare SNV in the DNA-binding domain, and two silent variants p.Pro36 =(rs1800370; C/T, 2%) and p.Arg213 =(rs1800372; T/C, 6%) were detected. In addition, 192 intronic alterations were found: All analyzed patients had at least two, 65% had four; the most common were rs2909430 and rs1625895. The rates of all variants were similar to the data for the European population published by the 1000 genomes project, phase3.

Conclusions: Although a larger study might provide additional insights, targeted sequencing as performed here did not reveal a major role of TP53 mutation in the pathobiology of SMN developing after treatment for childhood ALL.