The oral first-in-class phosphatidylinositol 3-kinase delta (PI3Kδ) inhibitor idelalisib in combination with the CD20-antibody rituximab has been approved for therapy of chronic lymphocytic leukaemia (CLL) back in 2014 and is indicated for the treatment of patients with at least one prior therapy or first-line treatment in presence of deletion 17p (del17p) or TP53 mutation in patients who are not eligible for any other drugs. Here, TP53 is linked to B-cell chronic lymphocytic leukemia.