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Chronic myelomonocytic leukemia and blastic plasmacytoid dendritic cell neoplasm. A case report and systematic review

2020; Wiley; Volume: 100; Issue: 3 Linguagem: Inglês

10.1002/cyto.b.21932

1552-4957

Andrea Espasa, Marc Sorigué, Gustavo Tapia, Marta Cabezón, Sara Vergara, Minerva Raya, José‐Tomás Navarro, Jordi Juncà, Lurdes Zamora, Blanca Xicoy,

Chronic Lymphocytic Leukemia Research

Plasmacytoid dendritic cells (pDCs) are part of the innate immune system and perform essential functions, such as antigen presentation and cytokine release. Malignant proliferations of pDCs are currently known as blastic plasmacytoid dendritic cell neoplasm (BPDCN) and were added in the 2008 revision of the World Health Organization (WHO) classification of hematological malignancies (Swerdlow et al., 2017). It is an aggressive disease defined by the clonal proliferation of blastic plasmacytoid dendritic cells precursors. Skin infiltration is almost universal, and bone marrow involvement, as well as that of lymphatic organs, is common. Blastic pDCs can be distinguished from their mature counterparts by morphology and expression of CD56 and CD33 (positive in 43% of BPDCN), among others. While the pathological diagnosis can be relatively straightforward when the clinical and pathological data show a matching picture, the coexistence of a monocyte-derived hematological malignancy makes the diagnostic process notably more difficult. Since these disorders are almost always CD4 and HLA-DR-positive and frequently express CD56, it can be very complex to establish whether the skin lesions are due to skin involvement by the monocytic malignancy or a BPDCN associated with it. In this setting, flow cytometry (FC) could be an important ancillary diagnostic tool. In this report, we describe a patient with CMML and BPDCN for whom FC played an essential role in distinguishing two phenotypically-similar, clonally-related, but ultimately different populations. We then conduct a systematic review of this association. A detailed materials and methods section can be found in the Supporting Information, including the antibodies, clones and fluorochromes used as well as relevant procedural aspects of immunohistochemistry staining and next-generation sequencing. Briefly, the flow cytometric analysis was carried out on peripheral blood and bone marrow collected on EDTA-containing 3 ml vacutainer tubes (Becton-Dickinson) and processed according to a standard stain-lyze-wash protocol within 24 hr. 100 μl of peripheral blood or 50 μl of bone marrow were mixed with 5 μl of each monoclonal antibody (all from Beckman Coulter, see Supporting Information, methods) and incubated in the dark, at room temperature for 10 min. After staining, the samples were lyzed with OptiLyse C (Beckman Coulter) for 10 min and then washed with FACSflow (Becton-Dickinson), at 1500 rpm for 5 min. After removing the supernatant and resuspending with FACSflow, 30,000 to 50,000 events were acquired on a 3-laser, 10-color, Navios flow cytometer (Beckman Coulter). For the cytometric analysis of the skin, a 1 cm punch biopsy was obtained, quickly placed in RPMI and minced right away with a scalpel tip. The RPMI-preserved cell suspension was processed according to the same stain-lyze-wash protocol. Kaluza software (Beckman Coulter) was used for all analyses. The figure shows the gating sequence, which included monitoring the stability of the acquisition over time and exclusion of doublets and debris. Monocytes were gated generously in CD33 and CD64 (bright expression with small-to-medium side light scatter). Plasmacytoid dendritic cells were gated as CD123++/HLA-DR++. Normal populations were used as internal controls. Fluorescence intensity was analyzed as median fluorescence intensity ratio (MFIr) that is, the ratio between the median expression intensity for the target antigen in the neoplastic population and the median expression intensity in T lymphocytes, except for HLA-DR for which a reliable internal control was unavailable and absolute values are used. The patient gave permission for the publication of this data. An 87-year-old man was seen to the hematology outpatient clinic due to thrombocytopenia (platelet count 126/nl [abnormal < 150/nl]), anemia (hemoglobin 91 g/L [abnormal < 120 g/L]) and monocytosis (1.4/nl [abnormal > 0.9/nl]). The physical exam was notable for violate, papulous skin lesions in the chest, back, and face, which had appeared 2 months earlier. The bone marrow smear showed signs of granulocytic dysplasia and 9% of monocytes. Immunophenotypic characterization of peripheral blood and bone marrow showed a mature monocytic population with expression of CD56 and CD123 (Figure 1a) although the percentage of classical monocytes (CD14bright, CD16-negative) was below 90% of total monocytes. G-banding karyotype was normal. NGS identified mutations involving TET2 (p.Met1333Asn) and ZRSR2 (p.Asn249Thr) and a diagnosis of chronic myelomonocytic leukemia (CMML) type 0 (low risk according to the CPSS [CMML-specific prognostic scoring system] and CPSS-Mol [molecular CPSS]). A skin punch biopsy of the lesions was taken. The pathological examination identified the presence of blastic cells with expression of CD4 and CD56, and negative for CD34, TdT, CD20, and CD3. Ki-67 was positive in 40% of cells. Mature neutrophils or monocytes were not seen. With this data, the histological examination could be consistent with both a blastic monocytic proliferation or BPDCN. Unfortunately, more specific markers of BPDCN (BDCA2, TCL1, DC2AP, or CLA) were not available. In order to better characterize this population infiltrating the skin, a new punch biopsy was obtained for FC analysis. Over 95% of the sample was made up by a single population, which was CD4-positive and showed bright expression of CD56, HLA-DR, and CD123. BDCA2 was positive, consistent with a diagnosis of BPDCN (Figure 1b). No monocytes were seen. The same myeloid NGS panel was run and the same two mutations were detected. An additional mutation in ASXL1 was also identified (p.Gln882*). In subsequent months, cytopenias worsened and alanine aminotransferase (ALT) and serum lactate dehydrogenase (LDH) increased. Treatment with low-dose cytarabine was started, with good hematological response, but no improvement in the skin lesions. Radiotherapy was administered to the largest lesions. As those visually regressed, and given that the patient had an acceptable performance status, total skin irradiation (TSI) was performed, with good response of the lesions. Nevertheless, cytopenias worsened further, even requiring blood transfusions. Bone marrow aspiration was repeated and showed increased cellularity, constituted by massive blast infiltration (91%). Those cells had abundant cytoplasm and, in many cases, pseudopodic prolongations. By FC, they were positive for CD4 and showed bright expression of CD56, HLA-DR, and CD123, consistent with BPDCN. NGS at this moment showed the same mutations in the three genes (TET2, ZRSR2, and ASXL1). Active treatment was discontinued and palliative care was started. He eventually passed away, 9 months after the first diagnosis. We performed a systematic review of the MEDLINE database with the MeSH terms "chronic myelomonocytic leukemia" and "chronic myelomonocytic leukemia," in combination with "plasmacytoid dendritic cell" and "plasmacytoid dendritic cells" (Supporting Information, results). The search was restricted to English and, potentially, Spanish publications. The search produced 24 entries, 22 of which were read in full. Two articles were found through additional searches. Seventeen publications were subsequently excluded. Therefore, seven studies were finally included (see the Supporting Information, results for the diagram of the systematic review process as well as the summary table of the results). A total of 13 patients with CMML and BPDCN have been reported since 2008 in three cases series and four case reports. In the past few years, attention to the association between different hematological malignancies has increased. Molecular studies can establish the relationship between them and, where a clonal relationship exists, help understand the mechanisms of the underlying biological connection and the maturation stage of the common precursor. The association between CMML and BPDCN has previously been reported, and indeed our systematic review revealed the publication of a number of case reports and some case series, yet it is unclear how commonly they coexist. A prospective protocol including a complete skin exam and high sensitivity bone marrow and peripheral blood for the presence (and phenotype) of pDC in patients with CMML would be feasible and informative. This is particularly relevant because the systematic review also showed that monocytosis in BPDCN seems to be more commonly reactive rather than malignant, and that pDC proliferations in CMML are more commonly of mature DC than BPDCN. These two facts also underscore the complexity of the differential diagnosis of abnormal findings in the physical exam or blood tests in patients with these hematological malignancies and indicate that non-malignant monocytic or mature pDCs proliferations may be the first diagnostic option in patients with BPDCN and CMML, respectively. This is made even more complex by the coexpression of numerous markers between monocytic cell lineages and pDCs (CD4, HLA-DR) as well as the coincidence of abnormal markers expressed in neoplastic conditions (such as CD56). BDCA2 and other specific pDCs lineage markers are unavailable in many diagnostic laboratories, given the rarity of these diagnoses. In the case presented, the malignant monocytes were CD123-positive, which makes the differential diagnosis between skin involvement by monocytic/myelomonocytic neoplasms or BPDCN even more challenging. It should be noted that the differential diagnosis of BPDCN includes not only CMML but also other myeloid disorders, such as acute myeloid or monocytic leukemia. This is due to a number of shared features, such as blastoid cells, expression of CD123 and HLA-DR and, particularly in monocytic leukemia, that of CD56 and CD4. These diagnoses should also be considered when BPDCN is suspected. The case presented shows the potential usefulness of FC in these patients. Indeed, despite expression of the same markers, the dot plots showed clearly distinct populations, based on intensity of expression of each marker as well as light scatter properties. Our experience with this patient suggests that running a FC test on skin lesions is worthwhile, given the potential upside and negligible downside. Both the CMML and BPDCN showed shared mutations in genes recurrently mutated in myeloid disorders (TET2 and ZRSR2), including CMML. This confirms the clonal relationship between the two. While molecular testing of CMML and BPDCN in the same patient has rarely been conducted, the published reports indicate shared molecular alterations, supporting the idea that both malignancies are related and stem from a common progenitor. In our case, the additional acquisition of ASXL1 mutation by the BPDCN is consistent with clonal evolution and transformation to a more aggressive neoplasm. In conclusion, we report a patient with clonally-related CMML and BPDCN in which FC was instrumental in establishing the diagnosis. FC could be an important ancillary tool for these patients. We thank the CERCA Programme/Generalitat de Catalunya and the Josep Carreras Foundation for institutional support. The authors declare no potential conflict of interest. Appendix S1: Supporting Information. Appendix S2: Supporting Information. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. 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