CRLF2 encodes a cytokine receptor that functions as a coreceptor for thymic stromal lymphopoietin (TSLP), forming a signaling complex with IL7R that activates STAT3 and STAT5 to promote hematopoietic cell proliferation. The gene plays a role in immune development and is central to Th2 cell differentiation, as demonstrated by its expression on IL-25 and IL-33-responsive T helper cells in atopic dermatitis. CRLF2 alterations are significantly associated with Philadelphia chrX|Y-like acute lymphoblastic leukemia (Ph-like ALL), a high-risk subtype occurring in 10% of children and 27% of young adults with ALL 1. CRLF2 rearrangements activate JAK/STAT signaling and are found in approximately 91% of Ph-like ALL cases harboring kinase-activating lesions 1. CRLF2-rearranged ALL shows particular enrichment in Down syndrome populations 2. Clinical trials have investigated JAK-directed tyrosine kinase inhibitors such as ruxolitinib for CRLF2/JAK pathway-mutant Ph-like ALL 3. Although precision medicine approaches using targeted kinase inhibition show promise in preclinical studies and case series, standard-of-care treatment protocols for CRLF2-driven ALL remain under investigation, with final results from dedicated clinical trials pending 3.