A case of blastic plasmacytoid dendritic cell neoplasm (BPDCN) without cutaneous lesion
Author: Binglong Wang 1
Editor: Weifeng Gao2
Chief Editor: Li Yang3
Reviewer: Baohong Yue4
1Department of Clinical Laboratory, The First Affiliated Hospital of Fujian Medical University, Fujian Province, China
2Department of Hematology, Beijing Luhe Hospital, Capital Medical University, Beijing, China
3Department of Clinical Laboratory, Shantou Central Hospital, Guangdong Province, China
4Department of Clinical Laboratory, The First Affiliated Hospital of Zhengzhou University, Henan Province, China
Figure 1.Peripheral blood (PB) smear showing tumor cells resembled lymphoblasts, with moderately dispersed chromatin, one to two inconspicuous nucleoli, and scant cytoplasm (Wright stain, original magnification ×1000)
Figure 2. Peripheral blood (PB) smear showing neoplastic cell with pseudopod-like cytoplasmic and irregular nuclei (Wright stain, original magnification ×1000)
Figure 3. Bone marrow (BM) aspirate smear showing neoplastic cells with small to intermediate size, scant cytoplasm, agranular, condensed chromatin and inconspicuous nucleoli (Wright stain, original magnification ×1000)
Figure 4. Bone marrow (BM) aspirate smear showing neoplastic cells with pseudopod-like cytoplasmic and cytoplasmic microvacuoles (Wright stain, original magnification ×1000)
Figure 5. Myeloperoxidase was negative in neoplastic cells (BM, original magnification ×1000)
Figure 6. Periodic Acid-Schiff was positive in neoplastic cells (BM, original magnification ×1000)
Figure 7. Flow cytometry immunophenotype of bone marrow revealed blast cells (red) were positive for HLA-DR, CD33, CD43, CD123, CD56, CD117 (partial), CD36 (partial), CD4 (partial).
Figure 8. Biopsy of cervical lymph node reportedly revealed blastic NK-cell lymphoma.
Figure 9. The bone marrow biopsy findings were consistent with BPDCN.
A 47-year-old man was referred and admitted to local clinics with pale, cough, expectoration, and neck lymphadenopathy which gradually spread to axilla and groin. On examination, there was no skin lesion and palpable hepatosplenomegaly. He lost 4kg in the last six months. Cough and expectoration were alleviated after anti-inflammatory treatment(details were unknown). However, the lymph nodes were still enlarged. So, he was referred and admitted to our hospital. A full blood count showed a leucocyte count of 3.0×109/L, hemoglobin of 102g/L and platelet count of 51×109/L. Serum levels of lactate dehydrogenase elevated to 641 U/L(normal range, 313–618 U/L). Computed tomography scan of the chest showed many enlarged nodes in the mediastinum and axilla. Lymphoblast-appearing cells (11%) were noted in peripheral blood smear (Fig. 1-2). Bone marrow examination showed 67.5% of blasts (Fig. 3-4). These cells were small to intermediate size, scant cytoplasm, agranular, condensed chromatin and inconspicuous nucleoli. Myeloperoxidase was negative (Fig. 5). Periodic acid-Schiff was positive in 94% abnormal cells (Fig. 6).
Immunophenotyping of bone marrow revealed the CD45low population (66.0%) was positive for HLA-DR, CD33, CD43, CD123, CD56, CD117 (partial), CD36 (partial), CD4 (partial), and negative for CD13, CD14, CD64, CD19, cMPO, cCD3, CD303, CD304 (Fig.7) . Chromosome analysis was normal. The neck nodes biopsy and immunohistochemistry were in keeping with blastic NK-cell lymphoma (Fig.8), while the bone marrow biopsy findings were consistent with blastic plasmacytoid dendritic cell neoplasm (BPDCN) (Fig.9). Finally, a diagnosis of BPDCN without cutaneous lesions was made.
BPDCN is a rare, aggressive hematologic malignancy derived from the precursors of plasmacytoid dendritic cells. The disease could occur at any age, but most patients are elderly, with a median/mean age at diagnosis of 60-67 years. The male-to-female ratio is 3.3:1[1]. BPDCN frequently manifests as cutaneous lesions, followed by dissemination to peripheral blood, bone marrow, and lymph nodes[2]. It was first reported and recognized by Adachi[3] in 1994. Many names have been used due to uncertain tissue origin initially, such as agranular CD4(+) natural kill-cell leukemia,CD4(+)/CD56(+) haematodermic neoplasm[4-5]. With the gradual understanding of this disease, Lucio et al. [6] proposed that this type of tumor was related to plasmacytoid dendritic cells in 1999, which was subsequently confirmed by multiple studies. The 2001 WHO Classification named it blastic NK-cell lymphoma based on its cytological and immunophenotypic characteristics [7]. In the 2008 WHO Classification, BPDCN was considered to originate from plasmacytoid dendritic cells precursors, which was grouped into “acute myeloid leukemia and related precursor neoplasms”[8]. With the rapid development of molecular biology, the gene expression profile of BPDCN was confirmed to be distinct from both AML and ALL[9], which validated its classification as a separate entity among the acute leukemias in the 2016 WHO Classification, rather than as a subtype of AML.
The BPDCN is composed of monomorphic, medium-sized tumor cells, with obvious blastic features resembling either lymphoblasts or myeloblasts. Nuclei display round or irregular, fine to slightly condensed chromatin and one to several small nucleoli. The cytoplasm is usually scant and appears greyish-blue and agranular by Giemsa staining. Some cells present pseudopod-like cytoplasm. The typical neoplastic cell has cirumferential cytoplasmic microvacuoles, which is presentedas pearl necklace. The neoplastic cells in BPDCN are negative for alpha-naphthyl butyrate esterase, naphthol AS-D chloroacetate esterase (CAE), and MPO, while PAS reactivity is strong [1].
The typical immunophenotype of tumor cells detected by flow cytometry is positive for CD4, CD43, HLA-DR and CD56, as well as plasmacytoid dendritic cell related antigens, i.e. CD123(bright), BDCA-2/CD303 and TCL1, but negative for all myeloid and lymphoid lineage antigens, i.e. CD3, CD20, CD79a, myeloperoxidase (MPO), CD11c, CD163 and lysozyme.Some cases variably express the CD2, CD5, CD36, CD38 and CD79a antigens, but not CD13 and CD16 generally [10-11]. However, CD4 or CD56 is negative in about 8% of cases which does not exclude the diagnosis if other PDC―associated antigens (in particular CD123, TCL1A, or CD303) are expressed[1]. The progenitor antigens, CD34 and CD117, are always negative. By immunohistochemistry, BPDCN express the same markers found by flow cytometric, with TCL1 expression. However, TCL1 is not specific for BPDCN, which could be positive in mature B-cell lymphomas and T-cell prolymphocytic leukemia[12]. Recently, the TCF4(E2-2) transcription factor, which is essential to drive PDCs development, was found to represent a faithful diagnostic marker for BPDCN[1]. Garnache-Ottou et al. [13] had proposed a scoring system (Table 1) for BPDCN based on surface antigen expression. Among the antigens generally overexpressed by BPDCN blasts, CD123 could serve as a therapeutic target of engineered monoclonal antibodies[14].
Table 1. Scoring system for pDC leukemia/BPDCN diagnosis[13]
Two thirds of patients with BPDCN have an abnormal karyotype. Specific chromosomal aberrations are lacking, but complex karyotypes are common. Six major recurrent chromosomal abnormalities have been recognized, involving del(5q21) or (5q34) (seen in 72% of cases), del(12p13) (in 64%), del(13q13-21) (in 64%), del (6q23-qter) (in 50%), 15q (in 43%), and loss of chromosome 9 (in 28%). Genomic abnormalities mainly involve tumour suppressor genes or genes related to the G1/S transition; the most recurrent being deletions of CDKN2A. Array-based comparative genomic hybridization shows recurrent deletions of regions on chromosomes 4 (4q34), 9 (9p11–p13 and 9q12–q34), and 13 (13q12-q31), with diminished expression of tumour suppressor genes (RB1, LATS2), whereas elevated expression of the products of the oncogenes HES6, RUNX2, and FLT3 is not associated with genomic amplification[1].
The main differential diagnosis is usually made with AML. The blasts of AML with monocytic differentiation can express CD4, CD56, and CD123 and BPDCN cells may resemble myeloblasts or monoblasts. Thus, demonstration of negative for MPO, lysozyme, and NSE is important, as positivity for any of these three markers would favor AML rather than BPDCN. One recent study suggested that a panel of immunohistochemical markers including MPO, CD56, CD123, TCL1, TdT, and myxovirus A was most helpful in distinguishing between AML and BPDCN [15]. Furthermore, BPDCN must also be distinguished from mature plasmacytoid dendritic cell proliferation (MPDCP) associated with other myeloid neoplasms (most commonly chronic myelomonocytic leukaemia, MDS, or AML). Unlike the tumor cells of BPDCN, the cells in mature plasmacytoid dendritic cell nodules have abundant, eccentric cytoplasm reminiscent of plasma cells and mature chromatin, which morphologically similar to normal PDCs. The PDCs in these nodules generally have the same phenotype as their normal counterparts, although in occasional cases aberrant single or multiple antigen expression (e.g. of CD2, CD5, CD7, CD10, CD13, CD14, CD15, and/or CD33) has been reported. Most importantly, CD56 is negative in most cases, or shows only focal and weak reactivity. The PDCs in MPDCP have a low Ki-67 proliferation index (<10%)and lack TdT and CD34 [1].
Here, we reported a 47-year-old man who was diagnosed with BPDCN without skin lesions, presenting with pancytopenia and lymphadenectasis. Such patient could be liable to be misdiagnosed as ALL based on morphological and histochemical results alone, so the comprehensive diagnosis of MICM and pathological biopsy combined with clinical manifestations is very important.
References
[1]Swerdlow SH, Campo E, Harris NL, et al. (Eds): WHO Classification of Tumours of Haematopoietic and Lymphoid Tissues (Revised 4th edition). IARC: Lyon 2017.
[2] Pilichowska ME, Fleming MD, Pinkus JL, et al. CD4+/CD56+ hematodermic neoplasm (‘blastic natural killer cell lymphoma’): neoplastic cells express the immature dendritic cell marker BDCA-2 and produce interferon. Am J Clin Pathol, 2007,128:445-453.
[3] Adachi, M., Maeda, K., Takekawa, M., et al. High expression of CD56 (N-CAM) in a patient with cutaneous CD4-positive lymphoma. Am J Hematol, 1994, 47(4), 278-282.
[4] Marafioti T, Paterson JC, Ballabio E, et al. Novel markers of normal and neoplastic human plasmacytoid dendritic cells. Blood, 2008, 111:3778–3792.
[5] Urosevic M, Conrad C, Kamarashev J, et al. CD4+CD56+ hematodermic neoplasms bear a plasmacytoid dendritic cell phenotype. Hum Pathol, 2005, 36:1020-1024.
[6] Lucio P, Parreira A, Orfao A. CD123hi dendritic cell lymphoma: an unusual case of non-Hodgkin lymphoma. Ann Intern Med, 1999, 131:549-550.
[7] Jaffe ES, Harris NL, Stein H, et al. World Health Organization classification of tumours of haematopoietic and lymphoid Tissues. Lyon: IARC Press; 2001.
[8] Vardiman JW, Thiele J, Arber DA,et al. The 2008 revision of the World Health Organization(WHO）classification of myeloid neoplasms and acute leukemia:rationale and important changes. Blood, 2009, 114(5):937-951.
[9] Sapienza, MR., Fuligni, F, Agostinelli, C, et al. Molecular profiling of blastic plasmacytoid dendritic cell neoplasm reveals a unique pattern and suggests selective sensitivity to NF-kB pathway inhibition. Leukemia, 2014, 28(8):1606-1616.
[10] Chaperot L, Bendriss N, Manches O, et al. Identification of a leukemic counterpart of the plasmacytoid
dendritic cells. Blood, 2001, 97:3210-3217.
[11] Petrella T, Bagot M, Willemze R, et al. Blastic NK-cell lymphomas (agranular CD4+CD56+ hematodermic neoplasms): a review. Am J Clin Pathol, 2005, 123:662–675.
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一例无皮损的母细胞性浆细胞样树突细胞肿瘤
作者：王炳龙 福建医科大学附属第一医院检验科
编辑: 郜伟峰 首都医科大学附属北京潞河医院血液科
主编: 杨 礼 汕头市中心医院检验科
审稿专家：岳保红 郑州大学第一附属医院检验科
病史摘要：男性，47 岁，出现颈部淋巴结肿大，质地韧，活动度可，无压痛，伴咳嗽、咳痰，呈淡黄色，后渐波及腋下、腹股沟淋巴结，无痰中带血，伴面色苍白，无低热、盗汗，无头晕、头痛，无恶心、呕吐，无鼻出血、牙龈出血，无血尿，无尿频、尿急、尿痛，无皮疹、关节痛，无口腔破溃，就诊于当地医院，予抗炎治疗(具体不详)后咳嗽、咳痰明显好转，淋巴结肿大无明显消退，半年内体重减轻约4 kg。
影像学检查：CT示肺部平扫未见明显异常；纵隔及双侧腋窝多发淋巴结肿大，请结合临床。
相关实验室检查：
血常规：
生化：
外周血涂片：可见原始细胞占11%
骨髓涂片：骨髓增生极度活跃，原始细胞约占67.5%，细胞体积大小不均，胞浆量少，核染色质较粗，可见核仁
细胞化学染色：POX阴性， PAS 94%阳性。
流式细胞学检查：CD45弱阳性细胞占有核细胞总数69.1%，HLA-DR+，CD33+ ，CD43+， CD123+，CD56+，部分表达CD117，CD36，CD4，CD13-，CD14-，CD64-，CD19-， cMPO-，cCD3-，CD303-，CD304-。
染色体核型：
颈部淋巴结活检：结合免疫组化符合母细胞性NK细胞淋巴瘤。
骨髓活检：结合免疫组化考虑母细胞性浆细胞样树突细胞肿瘤。
最后诊断：母细胞性浆细胞样树突细胞肿瘤（BPDCN）
病例聚焦：
一、定义和起源
母细胞性浆细胞样树突细胞肿瘤 (blastic plasmacytoid dendritic cell neoplasm，BPDCN)是一种罕见的、侵袭性的血液恶性肿瘤，起源于浆细胞样树突细胞的前体细胞，该病可于任何年龄段发病，但好发于老年60-67岁，男女比例为3.3:1[1]。常侵犯皮肤，其次是骨髓，外周血和淋巴结 [2]。它最早由Adachi[3]在1994年被报道和认识。最初，由于不能确定其组织来源，已经更换过好多名称，如无颗粒CD4+NK细胞白血病、无颗粒CD4+CD56+血液皮肤肿瘤等[4-5]。随着对该疾病的逐渐认识，1999年Lucio等 [6]首先提出此类肿瘤与浆细胞样树突细胞有关，随后被多个研究证实。WHO 2001根据其细胞学和免疫表型特征将其命名为母细胞性NK细胞肿瘤[7]。WHO 2008[8]将其命名为BPDCN，并将其划分在急性髓系白血病及相关前体细胞肿瘤里。后来，随着分子生物学地快速发展，发现BPDCN的基因表达与AML和ALL均不同[9]，因此，在最新的WHO 2016修订版中将其分离出来成为独立的一种疾病。
二、形态学特点
BPDCN的肿瘤细胞胞体中等大小，胞浆量少或中等，灰蓝色，嗜碱性不均匀，可见伪足突出(拖尾细胞)，典型的瘤细胞可见沿胞膜下特征性的呈珍珠项链样排列的空泡，极少许细胞可有少许粗大的紫红色颗粒，细胞化学染色α-萘酚-丁酸酯酶、氯乙酸AS-D萘酚酯酶 (CAE)和MPO均为阴性，PAS阳性，呈圆珠样、颗粒状或大块状阳性[1]。
三、免疫表型
流式细胞检测BPDCN典型的肿瘤细胞表现为系别抗原阴性（如B 细胞(CD20，CD79a), T 细胞 (CD3), 髓系抗原 (MPO)，单核细胞(CD11c， CD163，lysozyme)）表达HLA-DR，CD43，CD4，CD56以及浆细胞样树突细胞细胞相关抗原CD123、BDCA-2/CD303、TCL1。在淋系和髓系相关抗原中，CD7和CD33表达较常见。有些病例会表达CD2，CD5，CD36，CD38，CD79a，一般不会表达CD13,CD16[10-11]。8%病例可出现CD56或CD4阴性，但如果CD303、CD123和TCL1阳性并不能排除这一诊断[1]。病理免疫组织化学染色表达标志与流式检测的标志类似，TCL1阳性。但是TCL1阳性并不特异，因为在成熟B细胞淋巴瘤和T幼稚淋巴细胞白血病中也表达该抗原[12]，因此需要一系列相关抗原综合判断。Garnache-Ottou 等 [13]提出以细胞表面抗原表达为基础的 BPDCN 评分系统 (表 1)。该诊断标准为，肿瘤细胞不表达系别抗原，同时表达至少一种浆样树突细胞相关抗原如CD123, TCL1, CD2AP 和BDCA2/CD303。当总积分>2时，诊断成立。WHO 2016修订版 [1]中指出TCF4 (E2-2)转录因子被发现是BPDCN的一个可靠的诊断标志物，它对PDCs的发育起着至关重要的作用。在BPDCN原始细胞普遍过表达的抗原中，CD123可以作为单克隆抗体的治疗靶点[14]。
表1. BPDCN诊断积分系统[13]
备注：BDCA-2：CD303；BDCA-4：CD304
四、染色体和分子遗传学特点
2/3的BPDCN患者有核型异常。缺乏特异性染色体异常，但复杂核型常见。已报道6种主要的重现染色体异常，包括5q21或5q34(见于72%病例)、12p13(见于64%病例)、13q13-21(见于64%病例)、6q23-qter(见于50%病例)、15q(见于43%病例)和9号染色体缺失(见于28%病例)。基因异常主要累及肿瘤抑制基因或与G1/S转化相关的基因，最常见的是CDKN2A的缺失。基于阵列的比较基因组杂交显示染色体4 (4q34)、9 (9p11-p13和9q12-q34)和13 (13q12-q31)区域的重现性缺失导致肿瘤抑基因(RB1, LATS2)表达减少，而癌基因HES6、RUNX2和FLT3产物表达升高不伴有基因组扩增[1]。
五、鉴别诊断
由于本例BPDCN，缺乏皮肤损害，且细胞形态与髓系、淋系原始细胞相似，过氧化物酶阴性，PAS阳性，形态学上需与ALL相鉴别；免疫表型细胞表达CD33，CD4和CD123，部分表达CD117，需与急性髓系白血病AML-M5相鉴别。如果MPO、溶菌酶或NSE有阳性，那么考虑诊断为AML-M5而非BPDCN。有研究表明，同时检测MPO、CD56、CD123、TCL1和TdT、黏病毒A能够很好的鉴别AML-M5和BPDCN[15]。BPDCN可表达CD56，易与NK细胞白血病相混淆，因此在确诊BPDCN之前需要应用一系列髓系、单核细胞标记和BPDCN相对特异的CD303/CD304和TCL1进行鉴别。
此外，BPDCN必须与髓系肿瘤相关MPDCP（mature plasmacytoid dendritic cell proliferation，MPDCP）进行鉴别。MPDCP细胞形态上较成熟，与正常PDCs相似，常常累及皮肤（皮疹、斑点或丘疹，极少有皮肤结节）、淋巴结和或骨髓。MPDCP常常与髓系肿瘤有关，最常见的是CMML、MDS或AML伴单核细胞分化。MPDCP的PDCs除了表达PDCs相关抗原(CD123，CD303，CD2AP，TCL1)外，还表达CD2，CD5，CD7，CD10，CD13，CD14，CD15和CD33，但绝大部分不表达CD56,或表达强度极弱。 Ki-67增殖指数很低，常<10%，不表达TdT和CD34[1]。
参考文献：（同英文部分，略）
（责任编辑：张辉 河南宏力医院）
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