PI3K isoform-specific inhibition has the potential to improve clinical responses not only where targeting multiple isoforms with a combination of isoform-specific compounds is beneficial (e.g. solid tumours, functional redundancy between PI3K isoforms) but also where it may not be (e.g. chronic lymphocytic leukaemia, autoimmune inflammatory disease) [5]. Here, PIK3CD is linked to B-cell chronic lymphocytic leukemia.