When at a low nutrient level and metabolic byproduct accumulate, CAFs converted metabolic waste products (including lactate and ammonium) into energy-rich metabolites, which contributed to promoting tumor growth.53 Fong and collaborators found that breast cancer cell-secreted exosomal miR-122 could suppress the glucose uptake by the niche cells through downregulating PKM2 and GLUT1. Here, PKM is linked to breast cancer.