FAM9C is an X-linked gene encoding a nuclear-localized protein with dual roles in normal and pathological contexts. In testis, FAM9C is expressed exclusively and shows homology to SYCP3, a synaptonemal complex component involved in meiotic chromosome X 1. This expression pattern and structural similarity suggest FAM9C participates in meiotic cell cycle regulation and spermatid development, consistent with its Gene Ontology annotations. Genetically, FAM9C represents a candidate gene for nonobstructive azoospermia (NOA), identified through whole-genome sequencing in infertile males 2. Its location within low-copy repeat regions on Xp22.33-p22.31 may facilitate chrX rearrangements affecting fertility 1. Beyond its physiological function, FAM9C exhibits aberrant expression in hepatocellular carcinoma, where it functions as a cancer-testis gene promoting cell survival through the PI3K/Akt signaling pathway 3. FAM9C overexpression increases Akt phosphorylation and suppresses UV-induced apoptosis, while knockdown reduces anti-apoptotic capacity. This pathway dependence makes FAM9C a potential therapeutic target in HCC. The dual functionality—normal role in male germ cell development versus oncogenic role in liver cancer—highlights tissue-specific context-dependent signaling mechanisms.