Mutations in JAK1, such as A634D, V658F, and p.R629_D630del, are rare drivers of hematologic malignancies, including chronic eosinophilic leukemia (CEL) [101], and inflammatory syndromes through sustained signaling activity [102–104]. This evidence concerns the gene JAK1 and Chronic Eosinophilic Leukemia, Not Otherwise Specified.