In clinical practice, case studies for 2 patients refractory to tafasitamab + LEN reported tumor biopsies with no detectable CD19 26 and 7 days after last tafasitamab dose.36 Subsequent biopsies at 32 and 25 days post-tafasitamab, respectively, showed re-emergence of CD19 expression for these patients, leading the authors to suggest that sustained antigen blockade from a prior anti-CD19 treatment may delay subsequent CD19-targeted therapy.36 The gene discussed is CD19; the disease is neoplasm.