SGSM2 (small G protein signaling modulator 2) is a multifunctional protein with roles in both normal cellular processes and cancer biology. In melanocytes, SGSM2 functions as a GTPase-activating protein (GAP) that inactivates RAB32 and RAB38 by promoting their GTPase activity and disrupting the RAB9A-HPS4 interaction, thereby regulating melanosomal trafficking of melanogenic enzymes 12. Beyond this canonical function, SGSM2 demonstrates broad relevance to cancer pathogenesis through distinct mechanisms. In thyroid cancer, SGSM2 acts as a tumor suppressor by activating RAP1, which competitively inhibits RAS signaling and suppresses MAPK/ERK and PI3K/Akt pathways in RAS wild-type cells 3. In estrogen receptor-positive breast cancer, SGSM2 is a plasma membrane-associated protein that interacts with E-cadherin/β-catenin complexes and regulates cell adhesion and migration through modulation of focal adhesion kinase phosphorylation and cytoskeleton dynamics 4. Additionally, SGSM2 expression associates with improved chemotherapy sensitivity in rectal cancer 5 and lipid metabolism dysregulation in pancreatic cancer 6. SGSM2 also exhibits age-dependent effects on lipid metabolism 7 and may be relevant to subsyndromal symptomatic depression 8. These findings establish SGSM2 as a multimodal regulator with potential therapeutic applications across multiple cancer types.