APC2 and neoplasm: APC2 is a tumor suppressor that negatively regulates the Wnt/β-catenin signaling pathway. Downregulation of this tumor suppressor stimulates the Wnt/β-catenin pathway, which promotes cellular proliferation by upregulating and activating downstream genes, such as Cyclin-D1, c-Myc, and T cell factor (TCF) proteins.