PDGFRB and myeloid neoplasm: The BCR-ABL1 fusion oncogene defines chronic myeloid leukemia, a unique myeloid neoplasm in which monocytosis is uncommon.11 The platelet-derived growth factor receptors alpha and beta (PDGFRA—chromosome 4q12 and PDGFRB—chromosome 5q31-q32) are type III receptor tyrosine kinases.