JAK1 and neoplasm: Positive staining for JAK1 and JAK2 was observed in the tumor cell cytoplasm and membranes of a subset of patients as shown in representative images of negative, weak, moderate, and strong staining shown in Fig. 2A. Staining quantification of cytoplasmic JAK1/2 showed normal distribution of weighted histoscores, and membrane staining was scored as absent or present (Fig. 2B-C).