Cells in the body are all supported within a network of fibers made of collagen called the extracellular matrix. This matrix is what gives tissues their shape. As a more plain example, picture a steak. The muscle cells alone can’t give a steak its shape. There are tough bits in the meat too. Those tough bits are concentrated areas of collagen fibers that make up the extracellular matrix, which keeps that steak in the shape of a steak. However, in tumors, that connective fiber is even tougher and the cells are even more closely clustered together, which makes it harder for things like immune cells or even oxygen to get into the centers of these cancerous growths. This extra tension from the extracellular matrix in and around the tumors is known as “solid stress”. Dr. Timothy Padera’s lab at the Massachusetts General Hospital recently collaborated with another lab at the Boston University School of Medicine to find that an antihypertensive drug called “losartan” reduces solid stress in metastatic lymph nodes, which improves immune cell infiltration into cancerous tissue 15-fold so that lymphocytes can fight cancer cells more effectively. Multiple studies have shown that solid stress from tumors puts pressure on both blood and lymphatic vessels. So, relieving it opens the path for cancer-killing immune cells to come in and do their job. Now that this new use for losartan has been found, this could possibly be paired with immunotherapy to more effectively treat cancer. For those interested, here is the original study:
http://www.nature.com/articles/s41551-021-00766-1