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Very few data exist on when a particular thrombopoietin-receptor agonist (TPO-RA) is favored in clinical practice for the treatment of patients with immune thrombocytopenia (ITP), about novel risk factors for vascular events (VE) with these drugs, nor about predictive factors for therapy free responses (TFR). We conducted an observational, retrospective, long-term follow-up multicenter study from November 2016 to January 2018 of 121 adult ITP patients initiating TPO-RA between January 2012 to December 2014. Data reflected that a platelet count ≤25 × 109/l at the time when the TPO-RA was initiated was associated with a 2.8 higher probability of receiving romiplostim vs. eltrombopag (P = 0.010). VE on TPO-RA was related to previous neoplasia in patients over 65 years (50% vs. 2.2%, P < 0.001), and to previous splenectomy in younger patients (100% vs. 33%, P = 0.001). Receiving romiplostim as first TPO-RA with no subsequent TPO-RA switching was associated with a 50% likelihood of TFR after 2.9 years of therapy (3.3 years in chronic ITP patients). These real-world data help deciphering some areas of uncertainty, and offer insight into some of the most relevant challenges of ITP which may help clinicians make appropriate treatment decisions in the management of adult ITP patients with TPO-RA.

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Background . In clinical practice, tapering off thrombopoietin receptor agonists (TPO-RA) in immune thrombocytopenia (ITP) is considered if therapy is no longer needed due to a decrease in the disease activity favoring sustained treatment-free responses (TFR). To date, there are no predictors to identify when this approach is likely to be successful, other than earlier start of TPO-RA, and robust platelet responses. Aim. To evaluate clinical predictors of TFR in a real-world cohort of ITP patients treated with TPO-RA by dealing with confounding variables that could be minimized at the stage of the analysis. Methods. In this retrospective, multicenter study from 19 secondary and tertiary Spanish hospitals, patients aged >18 years with chronic ITP who had initiated TPO-RA (eltrombopag [EPG] or romiplostim [ROM]) between January 2012 and December 2014 were included. Data were collected from medical records (November 2016 to January 2018) on patient characteristics, history of disease and previous therapies, TPO-RA administration, response and discontinuation. Results. A total of 82 patients with a median age of 63 years (range 19-90 years), 59.9% females initiated TPO-RA (ROM, n=37; EPG, n=45). The median time from diagnosis of ITP to therapy with TPO-RA was 5.5 years (1.1-50.3 years). In all cases the TPO-RA was started with intention to treat indefinitely; the median initial doses of EPG were 350 mg/week (175-525 mg/week), and those of ROM 2.0 μg/kg/week (1.0-7.0 μg/kg/week). The median time on TPO-RA treatment was 2.9 years (0.1 to 5.6 years), and the median follow-up from start of TPO-RA until collection of data was of 3.9 years (1.3 to 5.6 years). A total of 29 patients (35.4%) switched TPO-RA during follow-up. The most frequent cause for switching was lack of efficacy (44.8% of cases -in all cases the initial TPO-RA was EPG-). Due to switching, 58 patients received ROM, and 53 were treated with EPG, yielding 122.3, and 100.8 patient-years of total exposure, respectively. During follow-up almost one half of the patients (47.6%, n=39) stopped TPO-RA. After a median of 1.4 years (0.1-3.3 yrs) under TPO-RA treatment, 19 patients (23.2% of the whole cohort) maintained TFR defined as platelet counts >50x109/l for a median follow-up of 2.8 years (1.5-4.4 years) in the absence of any platelet increasing drug. Remarkably, while the specific TPO-RA that was discontinued did not influence the probability to achieve TFR (P=0.582), there was a trend towards receiving ROM as first TPO-RA and attaining sustained responses (P=0.073), while switching TPO-RA negatively predicted TFR (P=0.010). In univariate analysis with logistic regression, switching TPO-RA was associated with a 6.4 risk of not achieving TFR (P= 0.019). The overall comparison of the Kaplan-Meier curves indicated an association (log-rank P=0.041) among the initial TPO-RA that was prescribed and the probability of TFR (Fig 1A), but the estimated median time to achieve TFR was not reached for either TPO-RA. When switching and initial TPO-RA were considered, patients receiving ROM and not experiencing switching were the best performing group in terms of achieving TFR; the median time to taper off the drug and sustain platelet responses was 3.3 years (95% CI 2.7-4.0 years) (Fig. 1B). Conclusion. In this observational research analysis, we have tried to minimize the possible bias of some studies that could mistakenly attribute TPO-RA induced TFR, when in fact it may be the natural course of the underlying disease. By analyzing a group of chronic ITP patients with a particularly poor baseline prognosis (median time from diagnosis 5.5 years) we address potential confounding variables by disease severity. Our data show that assuring that long duration under TPO-RA therapy is provided (median of 3.3 years), one half of chronic ITP patients treated with ROM and not undergoing switching can achieve TFR. Disclosures Mingot-Castellano: Roche: Consultancy; Bayer: Consultancy; Novartis: Consultancy; Takeda: Consultancy; Sobi: Consultancy; Amgen: Consultancy; Novonordisk: Consultancy; CSL Behring: Consultancy. Jarque:Abbie: Consultancy, Speakers Bureau; Alexion: Consultancy, Speakers Bureau; Janssen: Consultancy, Speakers Bureau; Grifols: Consultancy; Gilead: Consultancy, Speakers Bureau; CellTrion: Consultancy; Celgene: Consultancy, Speakers Bureau; Bristol-Myers Squibb: Consultancy, Speakers Bureau; Amgen: Consultancy, Speakers Bureau; Servier: Speakers Bureau; Roche: Consultancy, Speakers Bureau; Pfizer: Consultancy, Speakers Bureau; Novartis: Consultancy, Speakers Bureau; MSD: Consultancy, Speakers Bureau; Takeda: Consultancy, Speakers Bureau; Shire: Consultancy, Speakers Bureau; Shionogi: Consultancy, Speakers Bureau. Campos:Novartis: Speakers Bureau; Amgen: Speakers Bureau. Lopez Fernandez:Amgen: Consultancy, Speakers Bureau. Casado:Amgen: Consultancy, Speakers Bureau; Novartis: Consultancy, Speakers Bureau. Álvarez Roman:Amgen: Consultancy, Speakers Bureau; Novartis: Consultancy, Speakers Bureau; Bayer: Consultancy, Speakers Bureau; Pfizer: Consultancy, Speakers Bureau; Roche: Consultancy, Speakers Bureau; CSL Behring: Consultancy, Speakers Bureau; Sobi: Consultancy, Speakers Bureau; Takeda: Research Funding; NovoNordisk: Consultancy, Speakers Bureau.