Quality control initiative on the evaluation of the dysmegakaryopoiesis in myeloid neoplasms: Difficulties in the assessment of dysplasia.

Evaluation of megakaryocyte morphology is difficult but can be essential for the diagnosis of myelodysplastic syndromes (MDS) and other myeloid neoplasms. We agreed upon descriptions and provided images of megakaryoblasts and of normal and dysplastic megakaryocytes, which were used as a basis for assessing the concordance of expert morphologists in their recognition. We showed a high rate of concordance for the recognition of micromegakaryocytes and confirmed their strong association with hematologic neoplasia, including MDS. Concordance was also found to be good for the recognition of multinucleated megakaryocytes, which showed a significant association with MDS. However cytoplasmic abnormalities were found not to be useful in MDS recognition. The occurrence of appreciable numbers of nonlobulated and hypolobulated megakaryocytes in individuals without a myeloid neoplasm was confirmed. We demonstrated that subjects without a myeloid neoplasm can have some megakaryocytes that are assessed as 'dysplastic' or 'possibly dysplastic' and that to avoid over diagnosis of dysplasia, 'possibly dysplastic' forms should be excluded from the count of dysplastic cells. Our results demonstrate that the nature as well as the presence of megakaryocyte dysplasia is important in the diagnosis of MDS; although evaluation of 30 megakaryocytes is strongly recommended, it may be possible to recognize diagnostically important dysplasia when fewer megakaryocytes are present but highly diagnostic forms are seen.

The 2008 revision of the World Health Organization (WHO) classification of myeloid neoplasms and acute leukemia: rationale and important changes.

Recently the World Health Organization (WHO), in collaboration with the European Association for Haematopathology and the Society for Hematopathology, published a revised and updated edition of the WHO Classification of Tumors of the Hematopoietic and Lymphoid Tissues. The 4th edition of the WHO classification incorporates new information that has emerged from scientific and clinical studies in the interval since the publication of the 3rd edition in 2001, and includes new criteria for the recognition of some previously described neoplasms as well as clarification and refinement of the defining criteria for others. It also adds entities-some defined principally by genetic features-that have only recently been characterized. In this paper, the classification of myeloid neoplasms and acute leukemia is highlighted with the aim of familiarizing hematologists, clinical scientists, and hematopathologists not only with the major changes in the classification but also with the rationale for those changes.

Classification of acute leukemias.

Because of the increasing recognition of the importance of genetic events to the diagnosis and treatment of the acute leukemias, the proposed new World Health Organization (WHO) classification incorporates genetic aberrations and immunology as major defining features in addition to morphology. In a hierarchal approach, genetic changes have precedence in the acute myeloid leukemias and immunology and genetic changes have precedence in the acute lymphoblastic leukemias. Four major groups of acute myeloid leukemia are recognized: 1) Acute myeloid leukemias with recurrent genetic abnormalities, 2) Acute myeloid leukemia with multilineage dysplasia, 3) Acute myeloid leukemias, therapy related, and 4) Acute myeloid leukemia not otherwise categorized. Two types of acute lymphoblastic leukemia are recognized based on immunologic characteristics: precursor B lymphoblastic leukemia/lymphoma and precursor T lymphoblastic leukemia/lymphoma. Precursor B acute lymphoblastic leukemia/lymphoma is subclassified into prognostic genetic groups. Biphenotypic leukemia is recognized as a form of acute leukemia of ambiguous lineage.

Follicular pattern of bone marrow involvement by follicular lymphoma.

Five patterns of bone marrow infiltration by non-Hodgkin lymphoma or Hodgkin lymphoma are currently recognized, but a true follicular pattern of bone marrow involvement by follicular lymphoma has not been described. In 260 bone marrow trephine biopsy specimens involved by follicular lymphoma, we identified 12 cases with a follicular pattern of bone marrow involvement. The paratrabecular pattern was not present at all in 9, and it accounted for less than 10% of tumor burden in 3 cases. Malignant follicles in the bone marrow were similar to malignant follicles in the respective lymph nodes. Follicular dendritic cells were identified by immunohistochemical analysis. The true follicular pattern of bone marrow involvement by follicular lymphoma seems to be more frequent in women than in men. It is important to recognize this pattern of follicular lymphoma in the bone marrow because it is possible to misinterpret interstitial lymphoid aggregates as benign in the absence of the more characteristic paratrabecular pattern.

The value of anti-pax-5 immunostaining in routinely fixed and paraffin-embedded sections: a novel pan pre-B and B-cell marker.

Whereas L26 (anti-CD20) is well established as a B-cell marker of high specificity for use in paraffin-embedded tissues and JCB117 (anti-CD79a) is increasingly used, a comparable additional pan-B-cell antibody has hitherto not yet been identified. Here we have studied the use of a novel anti-pan-B-cell marker Pax-5 for use in diagnostic pathology. Pax-5 encodes for BSAP (Pax-5), a B-cell-specific transcription factor, the expression of which is detectable as early as the pro-B-cell stage and subsequently in all further stages of B-cell development until the plasma cell stage where it is downregulated. Pax-5 is essential for B-lineage commitment in the fetal liver, whereas in adult bone marrow this transcription factor is required for progression of B-cell development beyond the early pro-B (pre-BI) cell stage. Among the B-cell genes that are present in early B-cell development and are upregulated by Pax-5 are CD19 and Igalpha (CD79a). We have tested a commercially available anti-Pax-5 antibody (anti-BSAP, clone 24) in a series of 592 routinely fixed and paraffin wax-embedded biopsies, including lymph nodes, bone marrow, and various other organs containing lymphoid tissues. Pax-5 protein (BSAP) was detected in all cases of precursor and mature B-cell non-Hodgkin lymphomas/leukemias. In addition, in 97% of classic Hodgkin lymphomas, Reed-Sternberg cells expressed Pax-5. However, Pax-5 was not detected in any of the multiple myelomas, solitary plasmacytomas, and 4% of diffuse large B-cell lymphomas. Among those diffuse large B-cell lymphomas not expressing Pax-5 were only those with terminal B-cell differentiation. All T-cell non-Hodgkin lymphomas, including ALCL and lymphoblastic lymphomas and leukemias, were negative. There was a strong association between Pax-5 and CD20 expression. We conclude that anti-Pax-5 is an excellent pan-B and pan-pre-B-cell marker. We have found that anti-Pax-5 is superior to anti-CD20 in the diagnosis of pre-B acute lymphoblastic leukemia and classic Hodgkin lymphoma versus ALCL of T and "null" cell type. It was also useful in differential diagnosis between lymphoplasmacytic lymphoma and plasmacytoma. Even though there is an excellent correlation between CD20 and Pax-5 expression, anti-Pax-5 exceeds the specificity and sensitivity of L26 (anti-CD20) because of its earlier expression in B-cell differentiation and its ability to detect all committed B cells, including classic Hodgkin lymphoma.

The World Health Organization (WHO) classification of the myeloid neoplasms.

A World Health Organization (WHO) classification of hematopoietic and lymphoid neoplasms has recently been published. This classification was developed through the collaborative efforts of the Society for Hematopathology, the European Association of Hematopathologists, and more than 100 clinical hematologists and scientists who are internationally recognized for their expertise in hematopoietic neoplasms. For the lymphoid neoplasms, this classification provides a refinement of the entities described in the Revised European-American Lymphoma (REAL) Classification-a system that is now used worldwide. To date, however, there has been no published explanation or rationale given for the WHO classification of the myeloid neoplasms. The purpose of this communication is to outline briefly the WHO classification of malignant myeloid diseases, to draw attention to major differences between it and antecedent classification schemes, and to provide the rationale for those differences.