Correlative studies using multicolor immunohistofluorescence (IHF) showed that the PD-L1 expression in mastocytosis was heterogeneous, with only a subset of mast cells expressing PD-L1 in MCL (Figure 1A), while nearly all mast cells in CM were positive for PD-L1 (Figure 1B). The gene discussed is CD274; the disease is mastocytosis.