Do We Know What Causes Gastrointestinal Carcinoid Tumors?

Researchers have made great progress in understanding how certain changes in DNA can cause normal cells to become cancerous. DNA is the chemical in each cell that carries our genes, which control how our cells function. We look like our parents because they are the source of our DNA. But DNA affects more than the way we look.

Some genes control when our cells grow and divide. Certain genes that help cells grow, divide, and stay alive are called oncogenes. Genes that slow down cell division or cause cells to die at the right time are called tumor suppressor genes. Cancers can be caused by DNA changes that turn on oncogenes or turn off tumor suppressor genes.

Changes in 2 tumor suppressor genes are responsible for many inherited cases of neuroendocrine tumors and neuroendocrine cancers. Most inherited cases are due to changes in the MEN1 gene. A smaller number are caused by inherited changes in the NF1 gene.

Most neuroendocrine tumors and neuroendocrine cancers are caused by sporadic changes (mutations) in oncogenes or tumor suppressor genes. Mutations are called sporadic if they occur after a person is born, rather than having been inherited. The mutations that cause carcinoid tumors often affect the MEN1 gene, the same gene responsible for most familial neuroendocrine tumors and neuroendocrine cancers. But not much is known about exactly what causes these gene changes.

Doctors do know that carcinoid tumors start out very small and grow slowly. When patients have parts of their stomach or small intestine removed to treat other diseases, taking a close look under the microscope often shows small groups of neuroendocrine cells that look like tiny carcinoids. Researchers still do not know why some stay small but others grow large enough to cause symptoms.