In the presence of primary polycythemia, further investigations are indicated [3]: bone marrow analysis, showing panmyelosis (hypercellularity with tri-lineage growth) in polycythemia vera; bone marrow cytogenetic analysis (presence of the Philadelphia chromosome in CML); and molecular analysis (presence of the JAK2 V617F mutation in polycythemia vera and the BCR-ABL1 fusion gene in CML). The gene discussed is BCR; the disease is chronic myelogenous leukemia, BCR-ABL1 positive.