MEIS1 and undifferentiated (embryonal) sarcoma: As a result, several new entities of spindle cell tumors with monomorphic cytomorphology have recently been identified, including NTRK and other kinase-fusion positive spindle cell tumors (Chiang et al., 2018; Suurmeijer et al., 2019; Kao et al., 2020), undifferentiated sarcomas with BCOR-CCNB3 (Argani et al., 2017; Kao et al., 2018), MEIS1-NCOA2/1 (Argani et al., 2018; Kao et al., 2021), FUS-NACC1 (Rooper et al., 2023), EWSR1-NACC1 (Antonescu et al., 2021), FGFR1-TACC1 (Yau et al., 2022), and MEIS1-NCOA2 rearrangement (Coty-Fattal et al., 2024).