Effect of BTK inhibition in the bone microenvironment in multiple myeloma. Myeloma cells promote the development of the associated bone disease, and the bone disease promotes tumor growth and survival, resulting in a vicious cycle of increased tumor burden and increased osteolytic bone disease. BTK inhibition has multiple effects to (1) directly inhibit tumor growth, (2) directly inhibit osteoclastic bone resorption, (3) inhibit the release of osteoclast-derived tumor growth factors, and (4) prevent adhesion to bone marrow stromal cells (BMSCs) and release of BMSC-derived growth factors. The culmination of these effects is to reduce tumor burden and osteolytic bone disease. Professional illustration by Alice Y. Chen.