Before revision: Groups of cells (a macrophage, an endothelial cell, and a tumor cell) collectively known as tumor microenvironment of metastasis (TMEM) can allow tumor cells to enter blood vessels.
After revision: Groups of three cell types (a macrophage, an endothelial cell, and a tumor cell) collectively known as tumor microenvironment of metastasis (TMEM) can allow tumor cells to enter blood vessels.