Extra translocation +der(1q9p) is a prognostic indicator in myeloproliferative disorders.

An identical extra derivative chromosome resulting from a translocation between the long arm of chromosome 1 and the short arm of chromosome 9, +der(1q9p), has been observed in three patients with a myeloproliferative disorder. Two patients had polycythemia vera in transformation (erythroleukemia in one patient and refractory anemia in the second), whereas the third patient had myelofibrosis which later evolved into acute myelomonocytic leukemia. The two patients who developed overt leukemia did not receive any previous cytotoxic treatment. Non-isotopic in situ hybridization was performed in two patients, allowing for the localization of the breakpoints in 1q12 and 9q12. A similar rearrangement has been previously described in patients with polycythemia vera, either at diagnosis or in advanced stages of the disease. These data suggest that this chromosome abnormality may be consistently associated with myeloproliferative disorders showing a high propensity to transformation, which is not treatment related, and the finding of the +der(1q9p) may represent a poor prognostic sign when observed in the chronic phase.