CD33 and acute myeloid leukemia: A recent study has suggested discoidin domain receptor 1 (DDR1), a class of collagen-activated receptor tyrosine kinase (RTK) was highly upregulated on bone marrow (BM)-derived CD33+ leukemic blasts of acute myeloid leukemia (AML) patients, suggesting that the remodeled collagen IV in BM microenvironment could modulate the migration and adhesion of myeloid leukemia cells during leukemogenesis [32].