CD123 immunostaining patterns in systemic mastocytosis: differential expression in disease subgroups and potential prognostic value.

CD123 is the α-subunit of the interleukin-3 receptor; it represents a potential therapeutic target in systemic mastocytosis (SM) given its absent expression on normal/reactive mast cells (MCs) and aberrant expression on neoplastic MCs. We studied 58 SM patients to define CD123 expression patterns by immunohistochemistry and its clinical significance. Two hematopathologists independently scored bone marrow slides using predefined histologic parameters. In all, 23 patients had indolent SM (ISM), 10 aggressive SM (ASM), 23 SM with associated hematological neoplasm (SM-AHN) and 2 had mast cell leukemia (MCL). MC_CD123 expression was demonstrable in 37 (64%) cases; expression rates were 100%, 61%, 57% and 0% in ASM, ISM, SM-AHN and MCL, respectively (P=0.02). Focal proliferation of plasmacytoid dendritic cells (PDCs) around MC aggregates, suggesting a tumor-promoting role for PDCs, was noted in 44 (76%) cases, and was significantly higher in CD123-positive versus -negative cases (87% versus 50%, P=0.005). CD123 expression and its staining intensity had prognostic value in SM-chronic myelomonocytic leukemia and nonindolent SM patients, respectively. These observations suggest that targeting CD123 in SM may have direct (via MCs) and indirect (via PDCs) antitumor effects and clinical trials to that effect require laboratory correlative studies to address the observed target expression heterogeneity.

KIT(D816V+) systemic mastocytosis associated with KIT(D816V+) acute erythroid leukaemia: first case report with molecular evidence for same progenitor cell derivation.

A case of systemic mastocytosis associated with a clonal haematological non-mast cell lineage disease (SM-AHNMD), where the associated disease is acute erythroid leukaemia (erythroid/myeloid type), is reported. Interestingly, molecular studies showed the KIT(D816V+) mutation not only in the mast cells, but also in the myeloid blast population and the leukaemic erythroid cells. As is the case with most erythroid leukaemias, the patient had a very aggressive clinical course and died shortly after diagnosis. It is believed that this is the first reported case of systemic mastocytosis with erythroid leukaemia where the KIT(D816V+) mutation was detected in all three cell types. Molecular findings provide evidence for derivation of these seemingly morphologically distinct lesions from the same clonal precursor cell. From a practice standpoint, this case illustrates the importance of definitively diagnosing the associated non-mast cell lineage disease due to its prognostic implications.

Mantle cell lymphoma lacking the t(11;14) translocation: a case report and brief review of the literature.

The diagnosis of mantle cell lymphoma (MCL) requires a multifaceted approach with integration of morphology and immunophenotype, supported by cyclin D1 positivity or identification of t(11;14)(q13;q32). Interphase fluorescence in situ hybridisation (FISH) using a dual colour, dual fusion probe strategy for t(11;14) is a rapid test with high sensitivity and specificity for MCL, and is easily performed on routine bone marrow aspirate or peripheral blood specimens. This test has become the method of choice for many pathologists to confirm a diagnosis of MCL. This report describes a case of MCL with a normal (negative) FISH signal pattern for t(11;14) that was found to be cyclin D1 positive by immunohistochemistry in tissue sections. This case illustrates the need for additional testing when the t(11;14) abnormality is not identified but the morphology and immunophenotype are otherwise suggestive of MCL.