Pb1893: clonal evolution with bcl-2 amplification during venetoclax treatment

Topic: 4. Acute myeloid leukemia - Clinical Background: The B-cell Leukemia/Lymphoma 2 (BCL-2) protein has an anti-apoptotic function, conferring a greater survival to tumor cells that overexpress it. Specific BCL-2 inhibitors such as venetoclax represent a major breakthrough due to their cytotoxic efficacy in cells with BCL-2 overexpression, not only in chronic lymphocytic leukemia (CLL) but also in other hematological neoplasms such as acute myeloid leukemia (AML). However, resistance mechanisms have been described, such as BCL2 mutations that affect drug binding (G101V, D103Y, etc.), over-expression of pro-survival proteins like MCL-1 and BCL-xL, or mutations in other genes, e.g. FLT3 or TP53. However, to the best of our knowledge, BCL2 amplification in patients treated with venetoclax has not been described. Aims: Here we describe a patient diagnosed with AML with mutated TP53 who displayed a clonal evolution with the emergence of BCL2 amplification after the administration of antineoplastic treatment. Methods: Karyotype was performed on 20 metaphases obtained from an unstimulated mitogen culture with a resolution of 300 bands. BCL2 amplification was determined by Fluorescence in situ hybridization (FISH) in 200 interphase nuclei using XL BCL2 BA probes (MetaSystems). Next-generation sequencing (NGS) was performed with the 30-gene Myeloid Solution panel (SOPHiA Genetics) on a MiSeq (Illumina). Results: A 56-year-old female patient was diagnosed with AML with multilineage dysplasia. At diagnosis, a hypercellular bone marrow (BM) with a gap in the granulocytic and monocytic series was observed, associated with marked dyserythropoiesis, with a blast count of 16.2%. Cytogenetic analysis revealed a complex and monosomic karyotype, with a chromosomal formula of 44, XX, add(2) (p13), -5, -7, add(12) (p11.1), -16, +mar [20], without BCL2 amplification determined by FISH. The pathogenic TP53 c.487T>A (p.Y163N) variant was the only finding of interest in the NGS study, with an allelic frequency (VAF) of 58.7%. Germline origin was ruled out as the variant was absent in hair follicles. After the first induction cycle with the 7 + 3 scheme (cytarabine + idarubicin), refractoriness was observed, in addition to the appearance of 6% of nuclei with BCL2 amplification by FISH, while maintaining the TP53 variant (confirmed by PCR). A new therapeutic scheme was initiated with decitabine 10-venetoclax. A BM sample was studied 45 days after the start of treatment, observing a reduction of blasts to 3%, but with severe dyserythropoiesis suggesting disease persistence, with an evolutioned karyotype of 43, XX, add(2) (p13), -5, add(7) (p15), -12, -16 [9]/ 46, XX [11], along with an increase in the percentage of BCL2 amplification to 17% of the analyzed interphase nuclei by FISH. Summary/Conclusion: Clonal evolution of the leukemia was evidenced by the acquisition of BCL2 amplification alongside changes in the karyotype after antineoplastic treatment, and particularly following venetoclax administration, while maintaining the primary TP53 pathogenic variant. The increasing use of targeted therapies is improving remission and survival rates in most hematologic neoplasms, but it is also leading to the emergence of therapy-related clonal selections, as seen in this case, which could cause resistant relapses or even refractoriness. Understanding the mechanisms responsible for these phenomena would help to understand their relevance in the evolution of these patients. Keywords: Venetoclax, AML, BCL2, Amplification