BTK and lymphoma: The developed spirooxindole‐based PROTACs effectively inhibited and degraded BTK selectively with a biochemical IC50 value of 0.25 ± 0.03 μM, and this was translated to potent cellular activity in RAMOS lymphoma cells (IC50 = 0.50 μM) and the absence of cytotoxicity against the normal HEK293 cells (IC50 > 10 μM), demonstrating selective antitumor activity against B‐cell malignancies.