JAK2 and acquired polycythemia vera: As described in the RESPONSE clinical trial, almost 99% of PV cases are associated with somatic mutations in JAK2 (97.3% in JAK2 V617F with a mean variant allele frequency (VAF) of approximately 84% and 1.3% in exon 12) and are hypercellular with trilineage hyperplasia (panmyelosis) with evidence of an increased red cell mass [39].