TOB1 (transducer of ERBB2, 1) is a tumor-suppressor protein that functions as a negative regulator of cell proliferation through mRNA deadenylation and cell cycle control. TOB1 mediates its anti-proliferative effects by associating with deadenylase subunits of the CCR4-NOT complex 1, and recruits CNOT7 to facilitate mRNA deadenylation and decay. This mechanism reduces expression of cyclins D1 and CDK while inducing CDK inhibitors 1. Beyond mRNA regulation, TOB1 antagonizes oncogenic signaling pathways by inhibiting β-catenin-regulated transcription, antagonizing AKT signaling, and activating pro-apoptotic proteins like BAX while suppressing anti-apoptotic BCL-2 and BCL-XL 1. In cancer progression, TOB1 is frequently downregulated through promoter hypermethylation in esophageal squamous cell carcinoma 2. Homozygous TOB1 deletion promotes lung, liver, and lymph node cancer development in mice 1. Conversely, TOB1 overexpression inhibits cancer cell migration and invasion while restricting xenograft growth 1. MicroRNA-32-5p suppresses TOB1 expression in colorectal cancer, promoting radioresistance and metastatic phenotypes 3. In gastric cancer, TOB1 phosphorylation at T172 and S320 promotes malignant progression, while phosphorylation inhibition restores tumor-suppressive activity 4. Additionally, TOB1 in neutrophils regulates immunotherapy efficacy in gastric cancer 5.