Minimal residual disease assessment methods in patients with lymphoma. ASO, allele-specific oligonucleotide; CTC, circulating tumor cell; ctDNA, circulating tumor DNA; ddPCR, digital droplet polymerase chain reaction; IgNGS, immunoglobulin gene next-generation sequencing; NGS, next-generation sequencing; PBMC, peripheral blood mononuclear cell; PCR, polymerase chain reaction; RQ-PCR, real-time quantitative polymerase chain reaction; WT, wild type.