Immunofluorescent microscopy images of colorectal cancer tissues showing tumor cells and surrounding stroma including immune cells. Credit: Mayo Clinic ROCHESTER, Minn. — A discovery by Mayo Clinic researchers may help explain why immunotherapy hasn’t been helpful for many patients with metastatic colorectal cancer. In findings published in Clinical Cancer Research, the team identified specific proteins — fibronectin and smooth muscle actin — within colorectal cancer tissues that are associated with resistance to immunotherapy treatment. Immunotherapy…