The tumor microenvironment is the ecosystem that surrounds a tumor inside the body. It includes immune cells, the extracellular matrix, blood vessels and other cells, like fibroblasts. A tumor and its microenvironment constantly interact and influence each other, either positively or negatively.

“You can think of the tumor as a house and the microenvironment as its yard and its neighborhood,” says Sammy Ferri-Borgogno, Ph.D., instructor...