In this context, identifying mutations in MPN driver genes (JAK2, CALR, or MPL) or other myeloid neoplasm-associated genes (ASXL1, EZH2, TET2, IDH1, IDH2, SRSF2, and SF3B1) hints to the clonality of hematopoiesis and allows distinction from reactive conditions [1,34]. The gene discussed is CALR; the disease is myeloproliferative neoplasm.