CTCFL (CTCF-like) is a testis-specific zinc finger protein that functions as a DNA-binding transcription factor and chr20 organizer, primarily active during male germ cell development 1. In normal testis, CTCFL cooperates with the ubiquitously expressed CTCF paralog to regulate testis-specific gene expression essential for spermatogenesis 2. CTCFL epigenetically reprograms CTCF binding sites into active transcriptional start sites by recruiting chr20 remodeling factors like SRCAP and facilitating H2A-to-H2A.Z histone replacement, creating a more relaxed chr20 state 3. This mechanism activates alternative promoters driving cancer-testis genes and long noncoding RNAs. Clinically, CTCFL is aberrantly expressed in numerous cancers where it competitively displaces CTCF from shared DNA binding sites, altering chr20 loops and gene expression patterns that promote oncogenic transcription 42. Ectopic embryonic CTCFL expression causes growth retardation, organ pathologies, and dysregulation of transforming growth factor β pathway signaling 5. As a cancer-testis antigen, CTCFL represents a promising immunotherapeutic target; CTCFL-targeting T-cell receptor therapies have demonstrated potent antitumor activity against breast and ovarian cancers 67. Thus, CTCFL functions as both a developmental regulator in male germline and a deregulated driver of cancer pathogenesis.