STK11 and Langerhans cell histiocytosis: Similarly, in a chronic lymphocytic leukemia (CLL) patient, treatment with PI3Kδ inhibitor led to a switch from lymphocytic leukemia to Langerhans cell histiocytosis (LCH) with acquired BRAF V600E and STK11 mutations, and loss of expression of B-cell lineage markers such as PAX-5 [148].