The reduced size of CD133+ populations following chemotherapy (rather than the increase observed in other cancers including rectal cancers and glioblastomas [42,43]) may lend further credence to support the notion that CD133+ is not the primary TIC marker in mCRC, as the CD133+ population in mCRC appears to be targeted by current standard care chemotherapy strategies. The gene discussed is PROM1; the disease is cancer.