Improved diagnostic screening and classification of clonal mast cell diseases by ultrasensitive KIT p.D816V detection Open Access

• KIT p.D816V detection by ultra-sensitive SuperRCA improves the demonstration of the clonal nature of the disease in MCAS and mastocytosis

• The new SuperRCA assay detects KIT p.D816V in a significant fraction of nc-MCAS, supporting a KIT associated molecular basis for anaphylaxis

Detection of KIT p.D816V is a cornerstone in the diagnosis and classification of mast cell activation syndromes (MCAS) and mastocytosis. However, KIT p.D816V may be undetected due to a low mutated cell burden in blood and bone marrow (BM) of many patients, particularly among those without skin lesions. These findings underscore the need for ultra-sensitive molecular techniques for the detection of KIT p.D816V in these clinical settings. Here, we evaluated for the first time the sensitivity and specificity of a novel Flow-SuperRCA® KIT p.D816V assay, compared to conventional ASOqPCR, through the analysis of 548 blood and BM samples from 337 adults MCAS and mastocytosis patients. Our results demonstrated greater sensitivity of the new technique vs ASOqPCR (limit-of-detection: 0.001% vs 0.01% VAF), with higher rates of positivity for KIT p.D816V in whole-blood and/or BM of 64% of monoclonal-MCAS (MMAS) and 55% of BM mastocytosis patients (p<.0001). Notably, the sensitivity of the new assay went even beyond that of ASOqPCR in purified BM mast cells (p<.0001). Additionally, clonality was newly identified in 18% of patients previously diagnosed with non-clonal-MCAS, who presented with a unique cutaneous MCA-related symptomatic profile. These results confirm the high-specificity and ultra-sensitivity of the Flow-SuperRCA® assay for the detection of KIT p.D816V, emerging as a well-suited whole-blood and whole-BM test for the diagnostic screening and classification of MCAS and mastocytosis patients. These findings further highlight the clonal nature of an unprecedently high fraction of patients who presented with anaphylaxis and MCAS, with important pathogenic, diagnostic and clinical implications.