FSTL4 (follistatin like 4) functions as a regulatory protein in the extracellular region that modulates BMP signaling pathways and cell differentiation processes. The protein plays a critical role in regulating BDNF-mediated signaling, where neuronal FSTL4 negatively regulates BDNF maturation and the neuron-glioma interaction through the FSTL4/BDNF/TrkB axis 1. In early human development, FSTL4 is uniquely expressed at high levels in 8-cell embryos, suggesting novel developmental roles 2. FSTL4 serves as a potential biomarker in multiple disease contexts, including amyotrophic lateral sclerosis where it is significantly altered in cerebrospinal fluid compared to healthy controls 3. The gene shows associations with cancer susceptibility, particularly in colorectal and prostate cancers through Hardy-Weinberg equilibrium analysis 4. Additionally, FSTL4 is involved in malignant transformation processes, with its expression regulated by DNA methylation and miRNAs during aflatoxin B1-induced hepatocellular carcinoma development 5. Novel fusion genes involving FSTL4, such as ITPR2-FSTL4, have been identified in pediatric peripheral T-cell lymphomas 6, highlighting its potential role in oncogenesis and therapeutic targeting.