Background: Monopolar Spindle 1 (MPS1) kinase regulates the spindle assembly checkpoint (SAC) which ensures proper division of chromosomes during mitosis. MPS1 is overexpressed in several tumors, including hepatocellular carcinoma (HCC), where it correlates with tumor features and poor overall and disease-free survival. NMS-01940153E is a novel, highly potent and selective small molecule inhibitor of MPS1 kinase with long residence time and strong preclinical anti-tumor activity in different tumor types. In HCC lines, specifically, NMS-01940153E showed ~2-Log higher anti-proliferative activity compared to sorafenib, lenvatinib, and regorafenib. In a previous open-label first-in-human (FIH) study, CL1-81694-001 (EudraCT 2014-002023-10), signs of activity in HCC were detected. Recently, the treatment paradigm for advanced HCC has changed, with immunotherapy combinations in first line and TKIs shifted in later lines. However, the overall prognosis of patients with advanced HCC remains poor, and there is a strong need of new drugs in this setting. NMS-01940153E novel mechanism of action, inhibiting the SAC and interfering with genomic stability in HCC, may offer a new therapeutic option in HCC. Based on the promising FIH results, a Phase I/II study, MPSA-153-001 (EudraCT 2020-001002-26), was initiated in patients with HCC previously treated with more than one systemic therapy. Methods: The Phase II part of the MPSA-293-001 trial is designed as a two-stage study with an interim analysis for futility and safety rules for unacceptable toxicity. The primary objective is to assess the antitumor activity of NMS-01940153E in adult patients with unresectable HCC previously treated with systemic therapy measured as objective response rate (ORR) by investigator-assessed RECIST 1.1. Secondary endpoints are safety, PK, ORR as measured by investigator-assessed mRECIST, DoR, PFS and OS. Exploratory endpoints include biomarkers. NMS-01940153E is administered IV, on days 1, 8 and 15 every 4 weeks at the RP2D of 100 mg/m²/wk, which showed PK in a predicted active range. Key eligibility criteria are 1) diagnosis of HCC; 2) disease progression on standard-of-care treatment including an immune checkpoint inhibitor as first line and at least one TKI; 3) no more than 3 prior systemic treatment lines. Interim evaluation for futility will be undertaken as soon as the first 10 evaluable patients will be enrolled. If at least 1 responder is observed with no safety issues, enrollment will proceed up to 38 evaluable patients. Otherwise, the study will be terminated for futility. An independent DSMB will review the interim results and provide recommendation on the study progress. Recruitment is currently ongoing in Italy and Spain and an FDA “Study May Proceed Notification” was received in January 2023. Clinical trial information: NCT05630937.