If not activated, the endogenous levels of cAMP tend to increase and activate protein kinase A, resulting in the activation of downstream signaling pathways, such as mitogen-activated protein kinases (MAPKs), through the cAMP response element-binding protein (CREB), which is associated with cellular proliferation, tumor growth, and invasion [36,37], as shown in Figure 8. The gene discussed is CREB1; the disease is neoplasm.