The most prominent genes of this locus are programmed death ligands 1 and 2 (PDL1/PDL2), with the amplification of PDL1 being a hallmark of both classical Hodgkin and primary mediastinal B cell lymphoma, and Janus kinase 2 (JAK2), which is point-mutated in myeloproliferative neoplasms and other myeloid malignancies, and rearranged in PCM1-JAK2-positive myeloid/lymphoid neoplasms with eosinophila.
Ninety-two percent (23 of 25) of cutaneous mastocytosis (CM) cases and 1 of 2 with myelomastocytic leukemia expressed PD-L1, with no expression found in 15 healthy/reactive marrows, 18 myelodysplastic syndromes (MDSs), 16 myeloproliferative neoplasms (MPNs), 5 MDS/MPNs, and 3 monoclonal MC activation syndromes.