BTK and neoplasm: It is therefore not surprising that BTK inhibitors such as ibrutinib disrupt tumor cell-microenvironment interactions and mobilize tumor cells from the tissue sites into the peripheral blood, manifesting in an initial increase in lymphocytosis at therapy start [6]; however, patients expressing high levels of CD49d exhibit a lower degree of lymphocytosis under BTK inhibitor therapy, along with worse progression-free survival (PFS), compared to patients with low CD49d expression.