Molecular markers in MPDs. The indicated markers were evaluated in 42 ET, 22 PV, and 14 IMF patients. □ indicates that the marker is absent (ie, wild-type Jak2, normal expression of PRV-1, no Epo-independent growth, no EEC formation). ▪ indicates that the marker is present (ie, mutant Jak2V617F, overexpression of PRV-1, Epo-independent growth; EEC formation). For c-Mpl, ↓ indicates less than 40% of normal expression, whereas—indicates normal expression levels. Absence of a symbol indicates that the analysis was not performed. A “2” in the Jak2 analysis indicates that the patients were homozygous for the Jak2V617F mutant allele.