Plasmacytoid Dendritic Cell Dermatosis Associated to Myeloproliferative/Myelodysplastic Neoplasms

Flow Cytometry Profiling of Plasmacytoid Dendritic Cell Neoplasms

In this review, we aim to provide a summary of the diverse immunophenotypic presentations of distinct entities associated with plasmacytoid dendritic cell (pDC) proliferation. These entities include the following: (1) blastic plasmacytoid dendritic cell neoplasm (BPDCN); (2) mature pDC proliferation (MPDCP), most commonly seen in chronic myelomonocytic leukemia (CMML); and (3) myeloid neoplasms with pDC differentiation, in which pDCs show a spectrum of maturation from early immature pDCs to mature forms, most commonly seen in acute myeloid leukemia (pDC-AML). Our aim is to provide a flow cytometry diagnostic approach to these distinct and sometimes challenging entities and to clarify the immunophenotypic spectrum of neoplastic pDCs in different disease presentations. In this review, we also cover the strategies in the evaluation of residual disease, as well as the challenges and pitfalls we face in the setting of immune and targeted therapy. The differential diagnosis will also be discussed, as blasts in some AML cases can have a pDC-like immunophenotype, mimicking pDCs.

Granulomatous dermatitis in the context of chronic myelomonocytic leukemia: More than just reactive infiltrates. An illustrative case report with literature review

Traditionally, skin involvement in chronic myelomonocytic leukemia (CMML) has been considered to be either specific (leukemia cutis) or non-specific, with granulomatous dermatitis included in the latter group. More recently, the true nature of the myeloid cells present in the cutaneous infiltrates of this theoretically reactive dermatitis is being clarified with the use of new molecular techniques such as next-generation sequencing. The same mutations in bone marrow (BM) myeloid neoplastic cells and in the cells of cutaneous infiltrates have been found. We present the case of a 77-year-old man who presented with spread and treatment-resistant skin granulomatous lesions previous to the diagnosis of CMML. The same clonal mutations in SRSF2, IDH1, and RUNX1 were found in both skin and BM with resolution of the lesions after the initiation of azacytidine. In conclusion, we report an exceptional case in which specific granulomatous cutaneous lesions have preceded and allowed the earlier diagnosis of an underlying CMML and a review of all previous similar cases in the literature, including molecular alterations.

Classifications of cutaneous lymphomas and lymphoproliferative disorders: An update from the EORTC cutaneous lymphoma histopathology group

The classification of primary cutaneous lymphomas and lymphoproliferative disorders (LPD) is continuously evolving by integrating novel clinical, pathological and molecular data. Recently two new classifications for haematological malignancies including entities of cutaneous lymphomas were proposed: the 5th edition of the WHO classification of haematolymphoid tumours and the International Consensus Classification (ICC) of mature lymphoid neoplasms. This article provides an overview of the changes introduced in these two classifications compared to the previous WHO classification. The main changes shared by both classifications include the downgrading of CD8+ acral T-cell lymphoma to CD8+ acral T-cell LPD, and the recognition of entities that were previously categorized as provisional and have now been designated as definite types including primary cutaneous small or medium CD4+ T-cell LPD, primary cutaneous gamma/delta T-cell lymphoma, primary cutaneous CD8+ aggressive epidermotropic cytotoxic T-cell lymphoma, Epstein-Barr virus-positive mucocutaneous ulcer. Both classifications consider primary cutaneous marginal zone B-cell clonal neoplasm as an indolent disease but use a different terminology: primary cutaneous marginal zone lymphoma (WHO) and primary cutaneous marginal zone LPD (ICC). The 5th WHO classification further introduces and provides essential and desirable diagnostic criteria for each disease type and includes chapters on reactive B- or T-cell rich lymphoid proliferations formerly referred as cutaneous pseudolymphomas, as well as histiocyte and CD8 T-cell rich LPD in patients with inborn error of immunity. As already emphasized in previous lymphoma classifications, the importance of integrating clinical, histological, phenotypic and molecular features remains the crucial conceptual base for defining cutaneous (and extracutaneous) lymphomas.

Clinical, Histopathological and Molecular Spectrum of Cutaneous Lesions in Myelodysplastic Syndrome and Myeloproliferative Neoplasms (MDS/MPN): An Integrative Review

Myeloid neoplasms and acute leukemias include different entities that have been recently re-classified taking into account molecular and clinicopathological features. The myelodysplastic syndrome/myeloproliferative neoplasm (MDS/MPN) category comprises a heterogeneous group of hybrid neoplastic myeloid diseases characterized by the co-occurrence of clinical and pathological features of both myelodysplastic and myeloproliferative neoplasms. The most frequent entity in this category is chronic myelomonocytic leukemia (CMML) which is, after acute myeloid leukemia (AML), the main myeloid disorder prone to develop cutaneous manifestations. Skin lesions associated with myelodysplastic and myeloproliferative neoplasms include a broad clinical, histopathological and molecular spectrum of lesions, poorly understood and without a clear-cut classification in the current medical literature. The aim of this review is to describe and classify the main clinical, histopathological and molecular patterns of cutaneous lesions in the setting of MDS/MPN in order to improve the diagnostic skills of the dermatologists, hematologists and pathologists who deal with these patients.

Plasmacytoid dendritic cells in the setting of myeloid neoplasms: Diagnostic guide to challenging pathologic presentations

In this article, we describe three broad pathologic presentations of plasmacytoid dendritic cells (pDCs) that may be encountered in clinical practice, in which an association between pDCs and myeloid neoplasms is identified: (1) myeloid neoplasms with mature pDC expansion, most commonly seen in chronic myelomonocytic leukaemia (CMML); (2) myeloid neoplasms with pDC differentiation, in which pDCs show a spectrum of maturation from early immature pDCs to mature forms, most commonly seen in acute myeloid leukaemia (AML); (3) myeloid neoplasms associated with blastic plasmacytoid dendritic cell neoplasm (BPDCN), either stemming from the same precursor or representing an independent clonal process. Additionally, we also discuss AML with pDC-like phenotype, in which myeloblasts show immunophenotypic features that may mimic those seen in pDCs. Using these presentations, we provide a diagnostic algorithm for appropriate pathologic classification, while attempting to clarify and homogenize nomenclatures pertaining to different biologic states of pDCs.