Clinical and Molecular Challenges in Diagnosing Myeloproliferative Neoplasms with Low JAK2V617F Allelic Burden: A Single-Center Perspective and Literature Overview

Background/Objectives: The increasing sensitivity of molecular diagnostic techniques has led to the frequent detection of low-level JAK2 V617F mutations in individuals without overt myeloproliferative neoplasms (MPNs), creating uncertainty regarding their biological and clinical significance. This study aimed to evaluate the clinical relevance, thrombotic risk, and hematologic evolution associated with low JAK2 V617F allele burden. Methods: We conducted a retrospective single-center study including adult patients tested for JAK2 V617F between January 2016 and December 2023. Patients with a variant allele frequency (VAF) <2% who did not meet WHO or 2022 International Consensus Classification diagnostic criteria for MPN at baseline were included. Clinical characteristics, laboratory parameters, molecular findings, thrombotic events, and longitudinal ou--comes were analyzed. Results: Among two-thousand-three-hundred-seventy-two tested subjects, 55 patients (9.2% of JAK2-positive cases) harbored a low-level JAK2 V617F mutation (median VAF 0.35%). Over a median follow-up of 31.7 months, 12 patients (21.8%) progressed to overt MPN. Baseline VAF was significantly higher in patients who evolved to MPN compared to non-progressors. Thrombotic events occurred in 30.9% of patients and were associated with higher VAF values irrespective of MPN diagnosis. Serial molecular analyses showed stable persistence of the mutant clone over time. Conclusions: Low-burden JAK2 V617F mutations represent clinically relevant clonal events associated with thrombotic risk and potential disease evolution. These findings support the need for structured clinical and molecular follow-up even in the absence of initial diagnostic criteria.