KIT (D816V) Digital PCR in Systemic Mastocytosis

Systemic mastocytosis (SM) is a hematopoietic neoplasm characterized by an abnormal growth of clonal mast cells in bone marrow and other extracutaneous organs. Tyrosine kinase inhibitors, such as imatinib and avapritinib, have been evaluated to treat systemic mastocytosis.

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This test will detect the KIT D816V mutation only. A negative result does not exclude the possibility that other mutations in KIT are present, or that the KIT D816V mutation is present below the test limit of detection. This test was developed and its performance characteristics determined by Labcorp. It has not been cleared or approved by the Food and Drug Administration.

Nanoplate Digital PCR (dPCR); total genomic DNA is extracted and amplified using a multiplex digital PCR using wild-type and mutant-specific probes.

The assay is designed to detect the KIT D816V (KITc.2447A>T) mutation. Results are reported as percent mutated alleles. The mutation can be detected down to 0.03% mutated alleles.

KIT is a receptor tyrosine kinase involved in proliferation of mast cells, melanocytes, germ cells, and hematopoietic stem cells. Activation of KIT occurs upon binding of the stem cell factor ligand, which triggers autophosphorylation and dimerization of KIT. Activated KIT signals downstream protein kinase pathways, which induces cell proliferation and survival. The vast majority (>90%) of SM cases have a somatic A to T missense mutation at position 2447 in exon 17 of the KIT gene. This KIT D816V mutation (c.2447 A>T, p.D816V) results in the substitution of aspartate (D) to valine (V) at codon 816 in the kinase activation loop domain of the protein causing a conformational change in the receptor. This conformational change results in ligand-independent constitutive activation of KIT and leads to increased cell proliferation and accumulation in various organs, and a reduction in cell death. The detection of KIT D816V is one of the minor diagnostic criteria for SM per the WHO system. KIT mutation detection is correlated with the proportion of lesional cells in the sample as well as the sensitivity of the detection method employed.

Quantitative detection using digital PCR of the KIT D816V mutation may aid physicians in diagnosis and therapeutic monitoring of patients with SM. The reported values will allow clinicians to predict disease severity and/or monitor the effectiveness of treatment protocols and to detect increasing mutation levels that may be indicative of patient relapse. An effect of mutational dose on disease phenotype may also prove significant.