Background: Many pts with MF present with cytopenias, which are often progressive, and effective treatment (Tx) options that do not induce myelosuppression are limited. PAC, an oral kinase inhibitor with specificity for JAK2, FLT3, IRAK1, and CSF1R, was not associated with clinically significant myelosuppression in early trials. PERSIST-1 compares PAC vs BAT, excluding JAK2 inhibitors, in intermediate (Int)- to high-risk pts with MF, regardless of BL platelets (plt). At wk 24, a significantly greater proportion of PAC- vs BAT-treated pts achieved ≥ 35% spleen volume reduction (ITT: 19.1% vs 4.7%, p = 0.0003, 1º end point) and ≥ 50% reduction in Total Symptom Score (TSS; ITT: 24.5% vs 6.5%, p < 0.0001). This analysis examines long-term outcomes for pts with BL thrombocytopenia defined as plt < 100,000/μL or < 50,000/μL. Methods: Pts were randomized 2:1 to oral PAC 400 mg qd or BAT and stratified by DIPSS risk and plt count. Pts had splenomegaly ≥ 5 cm, TSS ≥ 13, and ANC > 500/µL. There were no restrictions on BL plt or hemoglobin. Pts could crossover from BAT to PAC after wk 24 or upon disease progression prior to wk 24. Results: At BL, ~1/3 of pts had thrombocytopenia (Table). Among evaluable PAC-treated pts on Tx at wk 60: 26% and 21% of pts with BL plt < 100,000/μL or < 50,000/μL achieved SVR ≥ 35%, respectively. No BAT-treated pt with BL plt < 100,000/μL achieved SVR ≥ 35%. At wk 48 (last assessment per protocol) 61% and 78% of evaluable PAC-treated pts with BL plt < 100,000/μL or < 50,000/μL achieved ≥ 50% reduction in TSS, respectively, increased from 42% and 32% at wk 24. In PAC-treated pts with thrombocytopenia, mean plt count and hemoglobin increased from BL to wk 60 (Table). Following crossover from BAT to PAC, of evaluable pts with BL plt < 100,000/μL or < 50,000/μL, 31% and 31% achieved SVR ≥ 35% (best response after crossover). Conclusions: In pts with MF and BL thrombocytopenia, Tx with PAC led to durable reductions in spleen volume and symptom burden including in pts with BL plt < 50,000/μL. Clinical trial information: NCT01773187