Data also showed that mutant CALRs are secreted from clonal cells that do not express TpoR and the plasma form behaves like a cytokine, oligomerizing with endogenous mutant CALR at the surface of TpoR expressing cells; in this way the circulating form activates the TpoR on cells belonging to the MPN clone.13 Here, MPL is linked to myeloproliferative neoplasm.