RAB21 and cancer: In addition, Rab proteins are critical for integrin recycling and trafficking processes in cancer cells [219,239,240]: (i) Rab21 recognizes a conserved motif found in the α-tails of all integrins and controls integrin endocytosis [241,242]; (ii) Rab25 is expressed in specific epithelial and some cancer tissues [243] and drives α5β1 recycling [244]; and (iii) Rab4 and Rab5 contained within early endosomes are instrumental for integrin sorting to other cellular compartments.