Table 4.

Technologies for MRD detection.

MRD method	Description
MPFC	MPFC is based on immunophenotyping technologies. There are two current techniques: (1) leukemia associated immunophenotype uses individual-specific surface makers identified at diagnosis and follows these markers in subsequent assessments. (2) The “different from normal” method identifies aberrant surface marker profiles at follow-up irrespective of profiles at diagnosis and can identify immunophenotype shifts.121
dPCR	Conventional PCR assays amplify a segment of DNA exponentially creating multiple copies; therefore, these segments of nucleic acid can be quantified by comparing the number of amplification cycles and the amount of PCR copies with a reference sample. For dPCR, the exponential signal of PCR is converted into a linear digital signal. It is designed to provide an absolute nucleic acid quantification, making it superior for detecting MRD.122
ASO quantitative PCR	This technology uses an ASO probe for detection of specific mutations. ASO probes are synthetic DNA complementary to the sequence of a variable target DNA. A fluorogenic probe is designed for each individual tumor-specific MRD-PCR target.123
NGS	NGS is also known as high throughput sequencing, and is a technology that allows for massively parallel sequencing of multiple genes, whole exomes and genomes. It can be done in a single day, and is precise. There is a large variability in cost between whole genome sequencing, whole exome sequencing and targeted sequencing, where only chosen regions of interest are sequenced. There are a variety of different technologies and companies that run this testing, each with a unique list of targeted genes.120

ASO, allele-specific oligonucleotide; dPCR, digital polymerase chain reaction; MPFC, multiparametric flow cytometry; MRD, minimal residual disease; NGS, next generation sequencing.