When free amino acids are unavailable, cancer cells may recover amino acids from (a) extracellular proteins via macropinocytosis. MPS, macropinosome, Lys, lysosome, (b) entosis of living cells, or (c) phagocytosis of apoptotic bodies. d, in conditions of oxygen deficiency, which prevents the de novo desaturation of stearate (C18:0) into oleate (C18:1), monounsaturated fatty acids such as oleate (C18:1) can be recovered from extracellular lysophospholipids (LPL). MPC, macropinocytosis; SCD1, stearoyl-CoA desaturase 1. X represents a lipid head group.