Cancer cells are embedded in a protective and nourishing “niche”, an environment that cancer cells create by secreting proteins into their surroundings. Because cancer cells depend on their niche to survive and spread to other parts of the body, we believe that therapies designed to inhibit secretion could suppress cancer spread and thereby improve the length and quality of cancer patients' lives. Developing such therapies will require a better understanding of how secretion is activated in cancer. Our proposal will address this knowledge gap. Here we show that p53 protein loss, an established driver of cancer spread, enhances secretion by reprogramming the Golgi apparatus, a master regulator of protein transport in cells. We show that p53 loss activates the formation of a Golgi protein complex that controls secretion, and we have identified secreted proteins that are essential for lung cancer growth and spread. Furthermore, we have identified a drug that can block the formation of the Golgi protein complex, reduce secretion, and inhibit lung cancer growth and spread. In this application, we seek to elucidate the molecular underpinnings and therapeutic implications of the heightened secretion driven by p53 loss. In aim 1, we propose studies to elucidate how the Golgi protein complex enhances secretion and drives lung cancer progression. In aim 2, we propose studies to determine how the Golgi protein complex increases sensitivity to the drug we have identified. These studies will provide insight into how secretion is activated in cancer and may lead to new ways to target secretion in cancer patients.