Diagnosing polycythemia vera: conventional tools amid molecular options—case report and brief review

Create PDF

JAK2 V617F mutations are also seen in about 50 percent of cases of essential thrombocytopenia or primary myelofibrosis and in the majority of cases of refractory anemia with ring sideroblasts associated with marked thrombocytosis (RARS-T). Calreticulin and MPL mutations are seen in about 25 percent of cases of essential thrombocytopenia or primary myelofibrosis, but only rarely in PV or RARS-T; the latter also usually has an SF3B1 mutation.6 A number of laboratories now offer a myeloproliferative neoplasm diagnostic cascade starting with JAK2 V617F, followed by CALR, and lastly MPL. Testing stops once one of these virtually mutually exclusive mutations is found.

Returning to the case study, follow-up sequencing of exons 12–15 surprisingly found the V617F mutation after all. Importantly, there was a second mutation in exon 14 (L607N) that likely disrupted primer binding by the allele-specific assay, resulting in a false-negative study initially. This case has a couple of other interesting points. The patient was iron deficient despite an MCV of 90.1 fL. Perhaps his alcohol consumption caused this; he was on no medications associated with macrocytosis. The smoking history certainly presented a compelling explanation for reactive (secondary) polycythemia. However, the very high hemoglobin and low EPO level appropriately prompted further evaluation, with PV ultimately confirmed by sequencing of exons 12–15. Had the reference laboratory sequenced only exon 12, the two mutations in exon 14 would have been missed.

In follow-up 2.5 years later, the patient receives therapeutic phlebotomy every other month and has not needed cytoreductive therapy. In December 2015, his hemoglobin was 15.9 g/dL, RBC 7.25 × 10⁶/µL, MCV 70.3 fL, WBC 12.2 × 10³/µL, and platelets 231 × 10³/µL.

In summary, within the past decade a host of genetic abnormalities associated with myeloproliferative neoplasms have been discovered that can refine our diagnoses and may lead to molecular-targeted therapies. Yet the hematopathologist’s conventional tools—automated CBC, peripheral blood smear, and bone marrow morphology—continue to be the basis for formulating a differential diagnosis and directing the diagnostic evaluation in a reasonable and cost-effective manner.

References

1. Passamonti F. How I treat polycythemia vera. Blood. 2012;120(2):275–284.
2. Swerdlow S, Campo E, Harris NL, et al., eds. WHO Classification of Tumours of Haematopoietic and Lymphoid Tissue. 4th ed. Lyon, France: WHO Press; 2008.
3. Silver RT, Chow W, Orazi A, et al. Evaluation of WHO criteria for diagnosis of polycythemia vera: a prospective analysis. Blood. 2013;122(11):1881–1886.
4. Johansson PL, Safai-Kutti S, Kutti J. An elevated venous haemoglobin concentration cannot be used as a surrogate marker for absolute erythrocytosis: a study of patients with polycythaemia vera and apparent polycythaemia. Br J Haematol. 2005;129:701–705.
5. Reilly JT. Pathogenetic insight and prognostic information from standard and molecular cytogenetic studies in the BCR-ABL-negative myeloproliferative neoplasms (MPNs). Leukemia. 2008;22(10):1818–1827.
6. Tefferi A, Guglielmelli P, Larson DR, et al. Long-term survival and blast transformation in molecularly annotated essential thrombocythemia, polycythemia vera, and myelofibrosis. Blood. 2014;124(16):2507–2513.

Dr. Shaw is a hematopathologist at Marshfield Clinic, Marshfield, Wis.