Most notably, these include atrial fibrillation, dermatological toxicities, spontaneous bleeding and invasive fungal infection.4 Infectious complications could be due to potential immunosuppression, as previously discussed.12,48, –50 Currently, it is unclear whether these effects are BTK inhibitor class-related and most prevalent in early therapeutics used short-term in the treatment of B-cell malignancies. Here, BTK is linked to atrial fibrillation.