Though many stories can be told, we will concentrate on several proteins executing critical adapter functions in cells of the immune system, such as Bruton ́s tyrosine kinase (BTK), phosphatidylinositol 3-kinase (PI3K), and SH2-containing inositol phosphatase 1 (SHIP1), as well as in cancer cells, such as proteins of the rat sarcoma/extracellular signal-regulated kinase (RAS/ERK) mitogen-activated protein kinase (MAPK) pathway. Here, BTK is linked to cancer.