Relationship between circulating CD34⁺ cell count and granulocyte MPL-mutant allele burden in patients with myeloproliferative neoplasms. Data are shown in a box plot depicting the lower and upper adjacent values (lowest and highest horizontal line, respectively), lower and upper quartile with median value (box), and outliers (dots). Spearman rank test showed a significant direct relationship between circulating CD34⁺ cell count and MPL-mutant allele burden (P = .0001). Patients with mutant alleles >50% had a significantly higher number of circulating CD34⁺ cells than those with ≤50% (P = .0028).