Classification of Ph-Negative Chronic Myeloproliferative Disorders – Morphology as the Yardstick of Classification

Impact of World Health Organization (WHO) Revised Criteria-2016 on the Diagnosis of Polycythemia Vera

The diagnosis of polycythemia vera (PV) requires the integration of clinical and laboratory findings, bone marrow morphologic features, and JAK2 analysis. JAK2V617F (exon 14) mutation is found in 95% of PV cases. In PV, addition of characteristic bone marrow morphology as one of three major diagnostic criteria allowed reduced hemoglobin/hematocrit threshold for diagnosis to 16.5 g/dL/49% in men and 16 g/dL/48% in women. JAK2 mutation is still the third major diagnostic criterion in PV. Low serum erythropoietin level is now considered as minor criterion in PV and is used to detect cases, which are negative for JAK2 mutation. In this retrospective study, cases diagnosed as PV from January 2013 to December 2015 were reclassified using WHO 2016 criteria. Their clinical and laboratory parameters along with treatment and outcome were studied. Out of 26 patients of previously diagnosed PV, either definitively or provisionally, twenty-one were found to comply with the new 2016 revision of the WHO Criteria. Median age was 55.5 years, with a male preponderance. The median values of hemoglobin, hematocrit and platelets were 17.5 gm/dL, 56.7% and 493 × 10⁹/L, respectively. JAK2V617F was mutated in 17 cases. Bone marrow showed hypercellularity, panmyelosis and marked megakaryocyte dyspoiesis in all patients. All patients had normal oxygen saturation, confirming the primary nature of the disease. Our study, first of its kind in India, underscores the importance of the 2016 revision of the WHO document in detecting cases of masked PV.

Problems and pitfalls in grading of bone marrow fibrosis, collagen deposition and osteosclerosis - a consensus-based study

AIMS

In the era of potentially disease-modifying agents such as Janus kinase inhibitors, accurate grading and differentiation of bone marrow (BM) fibrosis has become more relevant to assess staging of disease and therapeutic effects. However, different fibrosis grading models have been used in the past without uniformity, including the proposal by the World Health Organization. Current scoring systems are based only on reticulin fibrosis. Therefore, additional assessment of collagen and the grade of osteosclerosis appear to be essential to discriminate all components of the complex BM fibrous matrix.

METHODS AND RESULTS

We evaluated problems and pitfalls regarding staining techniques and the interpretation of reticulin fibrosis on a total of 352 samples. Furthermore, we propose a minor modification of the current grading and separate scoring for collagen deposition and osteosclerosis. Reproducibility of gradings was tested among 11 haematopathologists in a blinded assessment. Overall, the inter-rater reliability of all three grading systems ranged between 0.898 and 0.926.

CONCLUSIONS

A standardized assessment of BM fibrosis with differentiation between reticulin, collagen and osteosclerosis is recommended to evaluate the various components of the fibrous matrix which may be delinked after therapy. In this regard, quality of staining and application of laboratory standards enable a highly reproducible scoring.

WHO classification of myeloproliferative neoplasms (MPN): A critical update

Although the revised World Health Organization (WHO) criteria for the diagnosis and classification of myeloproliferative neoplasms (MPN) were defined by a panel of expert hematopathologists and clinicians, controversy has been repeatedly expressed questioning the clinical usefulness and reproducibility of these diagnostic guidelines. In particular, the distinction between essential thrombocythemia (ET), early/prefibrotic primary myelofibrosis (PMF) and initial stages of polycythemia vera (PV) is still a matter of debate. In this context, it has been argued that clinical correlations with histological features were not firmly substantiated. On the other hand, recently published data from independently performed studies have repeatedly validated the reproducibility of the WHO criteria and provided persuasive evidence that discrimination of early/prefibrotic PMF has a significant impact on the risk of myelofibrotic and leukemic transformation. However, as has been explicitly required, the WHO concept is based on the recognition of characteristic bone marrow patterns and a consensus of clinical and molecular data.

BCR-ABL1--negative myeloproliferative neoplasms: a review of molecular biology, diagnosis, and treatment

In 2008, the World Health Organization expanded the classification of myeloproliferative disorders based on increasing amounts of molecular and cytogenetic data. Myeloproliferative neoplasms (MPN) that do not contain the BCR-ABL1 mutation include polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF). JAK2V617F is the best characterized mutation in BCR-ABL1-negative neoplasms, with an estimated prevalence of more than 95% in PV, 50% in ET, and 50% in PMF. Current diagnostic strategies are increasingly reliant on molecular markers, and their prognostic value continues to be investigated. The use of aspirin, hydroxyurea, and phlebotomy for PV and ET, and the use of androgens, steroids, chemotherapy, and radiation therapy for PMF continues to be the mainstay of therapy. The only potentially curative therapy is allogeneic hematopoietic stem cell transplantation, but treatment-related mortality remains high. There have been promising results from clinical trials that involve the JAK tyrosine kinase inhibitors TG101384 and INCB018424, but their role in future therapy is yet to be established. Despite the optimism, it is increasingly apparent that pathogenicity in BCR-ABL1-negative MPN is more complex than for chronic myeloid leukemia, and a pathognomonic mutation may not be forthcoming.

Myeloproliferative neoplasms: molecular pathophysiology, essential clinical understanding, and treatment strategies

To update oncologists on pathogenesis, contemporary diagnosis, risk stratification, and treatment strategies in BCR-ABL1-negative myeloproliferative neoplasms, including polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF). Recent literature was reviewed and interpreted in the context of the authors' own experience and expertise. Pathogenetic mechanisms in PV, ET, and PMF include stem cell-derived clonal myeloproliferation and secondary stromal changes in the bone marrow and spleen. Most patients carry an activating JAK2 or MPL mutation and a smaller subset also harbors LNK, CBL, TET2, ASXL1, IDH, IKZF1, or EZH2 mutations; the precise pathogenetic contribution of these mutations is under investigation. JAK2 mutation analysis is now a formal component of diagnostic criteria for PV, ET, and PMF, but its prognostic utility is limited. Life expectancy in the majority of patients with PV or ET is near-normal and disease complications are effectively (and safely) managed by treatment with low-dose aspirin, phlebotomy, or hydroxyurea. In PMF, survival and quality of life are significantly worse and current therapy is inadequate. In ET and PV, controlled studies are needed to show added value and justify the risk of unknown long-term health effects associated with nonconventional therapeutic approaches (eg, interferon-alfa). The unmet need for treatment in PMF dictates a different approach for assessing the therapeutic value of new drugs (eg, JAK inhibitors, pomalidomide) or allogeneic stem-cell transplantation.

The impact of peripheral blood values and bone marrow findings on prognosis for patients with essential thrombocythemia and polycythemia vera

The Philadelphia chromosome-negative (Ph-) chronic myeloproliferative neoplasms include the three well-known clinical entities polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF). Over time, patients with ET and PV may develop myelofibrosis (MF), and all three entities carry a risk of transformation into acute myeloid leukemia (AML). In a population-based survey during 1983-1999, we studied a total of 358 patients who were diagnosed with ET and PV in the city of Gothenburg, Sweden. At the time of diagnosis, evaluable bone marrow biopsy material was available from 280 of these patients. The current work was aimed at investigating the impact of peripheral blood counts, spleen size, and bone marrow biopsy findings at diagnosis on long-term survival and the risk of development of AML or MF in this well-defined unselected population. The variables evaluated were venous blood hemoglobin concentration, packed cell volume, white blood cell count, platelet count, and splenic enlargement; as to bone marrow biopsies, interest was focused on reticulin content, focal or generalized collagen formation, bone marrow cellularity, and megakaryocyte profile number. Over the median observation time of 15 yr, the patients with ET did not demonstrate any significant difference as to survival compared to the normal Swedish population (hazard ratio, 1.23; 95% confidence interval, 0.97-1.51; p= 0.089). The patients with PV, on the other hand, had a significantly shorter survival compared to general population (hazard ratio, 1.66; 95% confidence interval, 1.38-1.99; p< 0.001). A lower hemoglobin concentration at diagnosis of ET predicted poorer survival (p =0.0281), whereas patients with PV with splenic enlargement at diagnosis had a shorter survival (p =0.037). In the patients with ET, the risk of transformation to either MF or AML was significantly associated with low hemoglobin concentration and high white cell count at diagnosis (p =0.0037 and 0.0306, respectively). An increased reticulin content and hypercellularity in the bone marrow at diagnosis were also independent risk factors (p =0.0359 and 0.0103, respectively). The risk of transformation in patients with PV was significantly associated with splenic enlargement and increase in bone marrow reticulin content (p =0.0028 and 0.0164, respectively).

MicroRNA expression profiling of megakaryocytes in primary myelofibrosis and essential thrombocythemia

In primary myelofibrosis (PMF) and essential thrombocythemia (ET) the megakaryocytic lineage characteristically shows aberrant proliferation and maturation in which the regulatory microRNA (miR) system might be involved. Laser-microdissected PMF and ET megakaryocytes were analysed with real-time polymerase chain reaction (PCR) low density arrays comprising 365 microRNAs. The highest megakaryocytic expression levels were observed for miR-223, which is known to be expressed also in granulopoiesis. Cluster analysis revealed a tendency of disease-specific megakaryocytic microRNA expression profiles indicating that a complex shift of microRNA expression appears to be the underlying defect. Increased accumulation of miR-146b was observed in cellular stage PMF (p = 0.0125) but not ET megakaryopoiesis. In conclusion, this is the first microRNA profiling of in situ-derived PMF, ET and normal megakaryocytes.

Bone marrow morphologic features in polycythemia vera with JAK2 exon 12 mutations

The diagnosis of polycythemia vera (PV) requires the integration of clinical and laboratory findings, bone marrow morphologic features, and JAK2 analysis. JAK2(V617F) (exon 14) mutation is found in 95% of PV cases. Functionally similar mutations in JAK2 exon 12 have also been described, but a thorough bone marrow study has not been done. We identified 7 PV cases with exon 12 mutations; all had hypercellular bone marrow with erythroid hyperplasia. Small, atypical megakaryocytes predominated; atypical megakaryocyte lobation and abnormal chromatin distribution was identified in all cases. Rare clusters of megakaryocytes could be found but were typically subtle. Because JAK2 exon 12-positive PV cases lack the classic myeloproliferative morphologic features, bone marrow samples from the patients may be difficult to classify as myeloproliferative neoplasms. Clinically suspected PV with low serum erythropoietin and absent JAK2(V617F), together with the bone marrow findings of erythroid hyperplasia and subtle megakaryocytic atypia, should prompt an evaluation for an exon 12 mutation.

Quantification of fibrosis and osteosclerosis in myeloproliferative neoplasms: a computer-assisted image study

Evaluation of bone marrow fibrosis and osteosclerosis in myeloproliferative neoplasms (MPN) is subject to interobserver inconsistency. Performance data for currently utilized fibrosis grading systems are lacking, and classification scales for osteosclerosis do not exist. Digital imaging can serve as a quantification method for fibrosis and osteosclerosis. We used digital imaging techniques for trabecular area assessment and reticulin fiber quantification. Patients with all Philadelphia negative MPN subtypes had higher trabecular volume than controls (p<or=0.0015). Results suggest that the degree of osteosclerosis helps differentiate primary myelofibrosis from other MPN. Numerical quantification of fibrosis highly correlated with subjective scores, and interobserver correlation was satisfactory. Digital imaging provides accurate quantification for osteosclerosis and fibrosis.

Expression profiling of apoptosis-related genes in megakaryocytes: BNIP3 is downregulated in primary myelofibrosis

OBJECTIVE

In order to identify factors involved in the aberrantly regulated apoptosis of megakaryocytes in primary myelofibrosis (PMF), the mRNA expression of human megakaryocytes in situ was quantified by real-time polymerase chain reaction low-density arrays.

MATERIALS AND METHODS

The mRNA from 200 to 300 laser-microdissected megakaryocytes per case from PMF (n=22) and control (n=10) bone marrow was reverse-transcribed into cDNA by random priming and subsequently amplified by primer-specific cDNA amplification. The mRNA of corresponding total bone marrow cells was reverse-transcribed into cDNA without the following amplification. For relative mRNA quantification, custom-made TaqMan low-density arrays with a setup of 48 different genes were applied. In addition, methylation analysis and immunohistochemistry of a selected candidate gene were accomplished.

RESULTS

A trend toward an overall downregulation of apoptosis-associated genes could be observed in megakaryocytes, whereas the total bone marrow cellularity exhibited an overall upregulation of these factors. Among several candidates with statistically significant deregulation BCL2/adenovirus E1B 19 kDa interacting protein 3 (BNIP3) and protein kinase C beta1 were shown to be the most aberrantly expressed genes.

CONCLUSION

Apoptosis-related gene expression profiling of human megakaryocytes reveals a set of candidates, most notably BNIP3, indicating that the increase of megakaryocytes in myeloproliferative neoplasia might not only be the result of increased proliferation but also of disturbed apoptosis.