CCR2 and Increased total leukocyte count: We further proved the clinical relevance of CCR2+ cells detection by FCM during the longitudinal follow-up of a PV patient who underwent a first bone marrow re-assessment in 2019, when transition into post-PV was suspected upon increased spleen size (longitudinal diameter of 14.5 cm vs 12.8 cm at PV diagnosis), increased LDH levels (1.4 UNL) and worsening leukocytosis.