P1639: utility of next generation sequencing techniques to evaluate possible causes of refractoriness to treatment with eltrombopag in adult patients with primary immune thrombocytopenia (itp) in spain.

Background: Primary immune thrombocytopenia (ITP) is an autoimmune acquired disease characterized by low production and increased platelet destruction. Thrombopoietin receptor agonists (TPO-RAs) i.e. eltrombopag, romiplostim and avatrombopag are currently used as second line treatment for ITP. Eltrombopag has demonstrated high response rates (≥80%) both in clinical trials and in routine practice studies. Nevertheless, some patients are refractory to this drug and do not attain a response when using the maximum eltrombopag approved dose of 75 mg per day after at least four weeks of treatment. Next generation sequencing (NGS) may help us discover underlying molecular biology variants that may be involved in eltrombopag refractoriness. Aims: To evaluate potential molecular markers of refractoriness to eltrombopag in ITP in routine clinical practice through the use of most recent molecular biology techniques (NGS). Methods: Nationwide multicenter, retrospective NGS study to investigate most important cell-signaling pathways that are involved in eltrombopag mechanism of action. So, 108 genes directly related to the downstream signaling of eltrombopag, cytokine signaling pathways, cytotoxic pathways, growth factors, adhesion molecules, apoptotic mechanisms and physiological mechanisms of platelet production are analyzed in peripheral blood from 35 refractory and 35 controls who responded to the drug. Results: Our refractory population involved 18/35 (51.4%) of male with a median age at diagnosis of 48 [range, 38-70] years and a median platelet count of 8 [range, 4-16] x 109/µL. At eltrombopag initiation, median time from diagnosis was 14 [range, 6-103] months with a median age of 60 [range, 41-75] years while median platelet count was 8 [range, 5-30] x 109/µL. 78.3% and 13.0% of cases were chronic and persistent ITP respectively. They have received a median of only two previous treatment lines [range, 2-4] (100% steroids, 42.8% IVIG, 40% splenectomy, 31.4% rituximab, 37.1% romiplostim). Eltrombopag treatment was maintained during 3 [range, 1-9] months as a median before discontinuation. No major grade 3-4 side effects were reported. On the other hand, characteristics of respondent controls were similar to refractory population. Statistical differences were observed regarding prior treatment lines, response and complete response rates (p=<0.001). Of the total sum of the NGS variants found and after artefacts eliminated a list of 53 variants were found. 13 variants with statistical significance (p≤0.05) between case and controls were relevant being some of them potentially associated with cancer and others considered benign instead. Variant two and seven are described in gastric and lung cancer respectively. Variants one, four, five, six, nine, eleven and thirteen belong to the second group. Variants three, eight, ten and twelve are not previously described and its significance is unknown (Table 1). Image:Summary/Conclusion: To the best of our knowledge, none of the 13 statistically significant variants reported here have ever been correlated with eltrombopag refractoriness although some of them have been previously associated with different cancers. Here we describe four non-previously published DNA variants and other nine non-previously described in ITP which role in megakaryopoesis and ITP drug refractoriness must be elucidated. It is needed more studies (including functional) to establish a more robust correlation between these variants and eltrombopag refractoriness.