SHMT1 and intestinal cancer: -Inhibition of PHGDH reduces cancer cell survival-Increased serine consumption enhances DNA damage repair in colorectal cancer cells-Blocking sources of serine is associated with anticancer effects-Restriction of serine and glycine intake inhibits the proliferation of intestinal cancer and lymphoma-Sertraline: reduces SHMT1/2 activity, increases radiosensitivity, and enhances treatment effectiveness in non-small cell lung cancer