FAM107B (heat shock-inducible tumor small protein, HITS) is an 18 kDa nuclear protein 1 involved in growth suppression and stress response. Primary function: FAM107B acts as a tumor suppressor, with forced expression diminishing proliferation in response to growth factors 2 and suppressing cellular responses to growth factors 1. Its expression is heat-shock inducible through HSF binding sites in its promoter 1. Mechanism: FAM107B mediates S100A4's inhibitory effects on gastric cancer cell proliferation and migration 2. It normalizes protein levels of SCA2-related cerebellar proteins, including Rgs8, Pcp2, Pcp4, Homer3, and Cep76 3. Disease relevance: FAM107B expression is significantly decreased in multiple cancer types including breast, thyroid, testis, uterine cervix, stomach, and colon cancers 4. Loss of expression correlates inversely with primary tumor size in breast and thyroid cancers 4. Recent genome-wide association studies identified FAM107B variants associated with limbic white matter microstructure in aging; its brain tissue expression significantly correlates with cognitive decline and Alzheimer's disease pathologies 5. It was also identified as a candidate gene for heat stress adaptation in sheep 6. Clinical significance: FAM107B functions as a therapeutic target; forced expression inhibits tumor xenograft proliferation 4, and antisense oligonucleotide targeting ATXN2 normalized FAM107B levels in SCA2 mouse models, improving motor function 3.