BTK and oculomucocutaneous syndrome: The Japanese product label for ibrutinib, a first-generation BTK inhibitor, lists 11 categories of adverse drug reactions (ADR) as identified/potential risks in the risk management plan (hemorrhage, bone marrow suppression, infection, arrhythmia, hypersensitivity, tumor lysis syndrome, liver failure/dysfunction, interstitial lung disease, secondary malignant tumors, leukostasis, and oculomucocutaneous syndrome) [5].