BTK and B-cell chronic lymphocytic leukemia: In all, 52.4% of the case pairs had genomic variants detected in the ctDNA sample only (and not on tissue analysis), underscoring the deep analytical sensitivity of liquid biopsy for detecting low-level disease clones, including clinically relevant resistance alterations such as Bruton tyrosine kinase (BTK) exon 15 p.C481X ibrutinib resistance mutations in chronic lymphocytic lymphoma (CLL) [68].