联合检测D2-40、calretinin及HBME-1在浆膜腔积液细胞学鉴别诊断中的意义

目的 观察D2-40、calretinin及HBME-1在浆膜腔积液间皮和转移性癌细胞中的表达,评价其用于鉴别诊断的价值.方法 用细胞块技术对87例浆膜腔积液标本进行免疫组化检测,观察D2-40、calretinin和HBME-1在癌细胞和间皮细胞中的表达.结果 D2-40、calretinin和HBME-1标记间皮细胞的敏感度分别为48.1%、81.0%、77.2%,特异度分别为90.2%、69.5%、61.0%.三者联合的敏感度和特异度分别为70.9%和81.7%.三者标记卵巢癌腹水间皮细胞的特异性都不高.结论 D2-40、calretinin和HBME-1合用可辅助鉴别诊断转移性癌与间皮.     

Comparison of three cytologic preparation methods and immunocytochemistries to distinguish adenocarcinoma cells from reactive mesothelial cells in serous effusion

We assessed whether a panel of seven antibodies is useful in the differentiation of adenocarcinoma cells (ACCs) from reactive mesothelial cells (RMCs) in effusion samples and to determine optimal specimen preparation conditions for immunocytochemical analysis of effusion samples. Immunocytochemistry (ICC) was performed on three types of effusion preparations from the same effusion specimens: ethanol-fixed smears, ethanol-fixed cell-blocks, and formalin-fixed cell-blocks. Commercially available antibodies MOC-31, Ber-EP4, CA19-9, CEA, EMA, CA125, and HBME-1 were tested on RMCs from four samples of various etiology and 15 samples of adenocarcinoma from various primary sites. Ethanol-fixed smears showed strong immunoreactivity to all antibodies tested. The immunoreactivity of ethanol-fixed and formalin-fixed cell-blocks was significantly lower with all antibodies except CA19-9. Smear preparations are more sensitive than cell-blocks for immunocytochemical study. A panel of antibodies MOC-31, Ber-EP4, CA19-9, and CEA appears to be suitable to distinguish between ACCs and RMCs.     

Immunocytochemical panel for distinguishing between carcinoma and reactive mesothelial cells in body cavity fluids

The morphological evaluation of cytological specimens from body cavity fluids presents difficulties in the differential diagnosis between benign reactive mesothelial (RM) cells and adenocarcinoma (AC) or malignant mesothelioma (MM). The aim of our study was to investigate whether a panel of five different antibodies can offer reliable markers in the differential diagnosis of RM, AC, and MM in serous effusions. A total of 134 cytological specimens of serous effusions from 80 ACs, 50 RMs, and 4 MMs, previously stained with Papanicolaou stain, were selected retrospectively from our files and stained with anti-human mesothelial cell (HBME-1), calretinin, epithelial specific antigen (MOC-31), Ber-EP4, and BG8. Statistical significance was found with HBME-1, calretinin, MOC-31, anti-human epithelial antigen (Ber-EP4), and blood group related antigen (BG8) when comparing AC vs. any type of mesothelial proliferation (MM or RM). The sensitivity of HBME-1 and calretinin for mesothelial cells was 98 and 100%, respectively, and the specificity was 71 and 80%, respectively. Both antibodies stained reactive mesothelial as well as MM cells, with calretinin showing a stronger intensity of immunostaining. The sensitivity of the stain for AC was 86.25% for MOC-31, 77.5% for Ber-EP4, and 67.5% for BG8, and, when combined, the sensitivity was 100%. Our data suggest that immunocytochemical studies performed on Papanicolaou-stained cytological smears with HBME-1, calretinin, MOC-31, Ber-EP4, and BG8 proved to be useful in the differentiation between metastatic AC and mesothelial proliferation. Probably, calretinin is a more preferred marker for mesothelial cells as evidenced by a more intense staining reaction.     

Significance of flower pot cells in effusion cytology

Cells with long polar hair‐like processes referred to as ‘flower pot cells’ are a rare but beautiful morphological feature observed in effusions of diverse etiologies. This report describes these cells in effusions seen in ovarian borderline serous tumours, malignant mesothelioma and in reactive mesothelial cells with or without accompanying malignant cells. These processes were better appreciated in air‐dried May‐Grunwald‐Giemsa stained smears.     

Embolization of mesothelial cells in lymphatics: the route to mesothelial inclusions in lymph nodes?

Aims : To provide evidence that lymphatic embolization is the mechanism for mesothelial inclusions in lymph nodes.  

Methods and results

A 60-year-old man with alcoholic cirrhosis and ascites had an umbilical hernia resected. The herniorrhaphy specimen contained numerous dermal and submesothelial lymphatic vessels filled by cells similar to the cells that lined the hernia sac. Most of the cells in lymphatics were submesothelial reactive cells, whose cytoplasm stained with antibodies against cytokeratins (AE1–AE3; 8,18), smooth muscle actin, vimentin, desmin and tissue polypeptide antigen (TPA). Some cells seemed to be superficial mesothelial cells, being positive with high molecular weight anticytokeratin antibody 34βE12. On ultrastructural study submesothelial cells with intermediate cytoplasmic filaments, rough endoplasmic reticulum and primitive cell junctions, and scanty superficial mesothelial cells with microvilli, tonofilaments and desmosomes were found in the lymphatics.  

Conclusions

Lymphatic dissemination of mesothelial and submesothelial cells is an uncommon and not well known phenomenon. Lymphatic dissemination is probably the route by which the mesothelial cells reach the lymphatic nodes. These cells may be mistaken for malignant cells.     

Diagnostic usefulness of EMA, IMP3, and GLUT-1 for the immunocytochemical distinction of malignant cells from reactive mesothelial cells in effusion cytology using cytospin preparations

To differentiate reactive mesothelial cells (RMs) from metastatic carcinoma and malignant mesothelioma (MM) in effusion cytology is crucial for the cytologic diagnosis and the management of the patients. In the present study, the immunocytochemical staining profile of the epithelial membrane antigen (EMA), the insulin-like growth factor-II mRNA-binding protein 3 (IMP3), and the glucose transporter-1 (GLUT-1) was examined to distinguish RMs from malignant cells. A total of 171 pleural (n = 87) and peritoneal (n = 84) effusion specimens, including 50 benign effusions with RMs, 11 MM effusions, and 110 metastatic malignant effusions, were evaluated for immunocytochemistry. EMA, IMP3, monoclonal GLUT-1, and polyclonal GLUT-1 immunoreactivity were observed in 26.0%, 6.0%, 20.0%, and 18.0% of RMs, respectively. In contrast to RMs, the immunoreactivity in MM was 100%, 36.4%, 100%, and 90.9%; adenocarcinoma (AC) was 100%, 80.8%, 81.7%, and 72.1%; squamous-cell carcinoma was 83.3%, 83.3%, 83.3%, and 66.7%. EMA, IMP3, mGLUT-1, and pGLUT-1 expressions were observed in 98.4%, 65.6%, 88.5%, and 75.4% in the pleural effusion with malignant cells, and 100%, 88.3%, 78.3%, and 71.7% in ascites containing malignant cells, respectively. The findings of the present study indicate that the immunocytochemical staining for EMA, IMP3, and GLUT-1 is a useful diagnostic tool for distinguishing effusions containing malignant cells from those that contain benign cells, and in particular, we suggest that the combination of mGLUT-1 and EMA, and IMP3 and EMA are extremely useful in pleural effusion and in ascites, respectively.     

Scoring system for differential diagnosis of malignant mesothelioma and reactive mesothelial cells on cytology specimens

Cytology is the only useful tool in the detection of malignant mesothelioma (MM) at an early stage. No other methods, such as immunocytochemistry or electron microscopy, are available to distinguish MM from reactive mesothelial cells (RMC). Some objective analysis of cytology specimens is necessary. On the basis of our case review and cytological features described in previous articles, we developed a scoring system for malignant mesothelioma (SSMM) of effusion cytology to distinguish MM cells from RMC. Mesothelioma cells in effusions from 22 patients (20 pleural and 2 peritoneal mesotheliomas) were compared with RMC from 20 patients without obvious tumor cells and 50 effusions containing metastatic carcinoma cells. The SSMM is based on characteristic features of mesothelial and malignant cells. The total achievable score is 10 points: one point each is given for variety of cell size, cyanophilic cytoplasm with villosity/windows/bleb, sheet‐like arrangement, mirror‐ball‐like cell clusters, nuclear atypia, and cannibalism, respectively. Further two points each are ascribed for acidophilic large nucleoli and multinucleated cells with more than eight nuclei. The total score for each of the 22 mesotheliomas was more than 5 points. On the other hand, all RMC and the 50 metastatic carcinoma cases scored less than 3 points, aside from two cases that were treated with OK432. No single characteristic feature was observed to be consistent within the 22 mesotheliomas analyzed. Ancillary use of immunocytochemistry, such as podoplanin (D2‐40) and calretinin, supported the diagnostic accuracy of the SSMM. SSMM is useful for the differential diagnosis of MM. Diagn. Cytopathol. 2009. © 2009 Wiley‐Liss, Inc.     

Intranodal benign thyroid tissue: significance of HBME-1 in differentiation from metastatic papillary thyroid carcinoma

The aim of this study was to determine the significance of HBME-1 immunostaining in the differentiation between intranodal benign thyroid tissue and metastatic papillary thyroid carcinoma in the lymph node. Immunohistochemically we examined normal-appearing intranodal thyroid tissue in four patients who did not show evidence of papillary carcinoma histologically or clinically. We also examined follicular-pattern-predominant papillary carcinoma with metastatic foci in the lymph nodes. Normal-appearing intranodal thyroid tissue and normal thyroid showed no immunopositivity for HBME-1. In contrast, all papillary carcinomas in both the lymph nodes and thyroid demonstrated strong positivity for HBME-1. HBME-1 was predominantly positive for the luminal surface of the tumor cells. The immunopositivity of the cuboidal and low columnar carcinoma cells was more intensive than that of the flat-shaped cells in the lymph nodes and thyroid. The results probably indicate that HBME-1 immunostaining is helpful in distinguishing between intranodal benign thyroid tissue and metastatic papillary carcinoma in lymph nodes. We emphasize that the HBME-1 reactivity should be evaluated in connection with the histological findings, and that positive and negative controls stained in parallel are necessary.     

地塞米松对大鼠胸膜间皮细胞水通道蛋白1表达的调节

 目的：观察胸膜间皮细胞水通道蛋白1（AQP-1）的表达及地塞米松（Dex）对其表达的影响，为进一步研究胸水治疗的机制提供实验依据。方法:体外培养大鼠胸膜间皮细胞，细胞鉴定后，采用免疫细胞化学、RT-PCR方法检测AQP-1表达；应用Western blotting检测以不同浓度Dex（10^-8、10^-7、10^-6、10^-5、10^-4 mmol/L）处理细胞 24 h 及以10^-4 mmol/L Dex处理细胞 6 h、12 h、24 h、36 h、48 h、72 h后AQP-1表达情况。结果:发现胸膜间皮细胞存在AQP-1表达， 10^-8、10^-7、10^-6、10^-5、10^-4 mmol/ L Dex干预胸膜间皮细胞 24 h 后，AQP-1蛋白表达量(积分吸光度)分别为755.04±19.81、843.72±19.41、862.96±26.53、694.80±32.00、938.08±13.32，分别高于正常对照组（372.90±16.46） 2.02、2.26、2.31、1.86、2.52倍 (P<0.01)，AQP-1表达升高与地塞米松浓度无关；以10-4 mmol/L Dex干预细胞 6 h、12 h、24 h、36 h、48 h、72 h 后，AQP-1蛋白表达量分别为：554.14±23.57、917.78±38.62、1 587.20±61.22、1 322.09±28.65、918.40±26.62、1 117.60±51.32，分别高于正常对照组（495.91±23.12）1.12、1.85、3.20、2.67、1.85、2.25倍(P<0.01)，AQP-1表达与地塞米松作用时间有关。结论:胸膜间皮细胞存在AQP-1表达，地塞米松对胸膜间皮细胞AQP-1表达有明显的增强性调节作用，具有时间依赖性。     

HBME-1 and CK19 are highly discriminatory in the cytological diagnosis of papillary thyroid carcinoma

The cytologic diagnosis of papillary thyroid carcinoma is straightforward in most instances. However, there are some mimics including goitrous nodules and Hurthle cell neoplasms. Many studies have shown the combination of HBME-1 and CK19 expression to be useful in reaching a correct histologic diagnosis on tissue sections. We aim to assess the value of these markers in the setting of cell blocks prepared from needle aspiration specimens. We performed immunohistochemical staining of HBME-1 and CK19 on cell block material from 22 thyroid nodules that also had follow-up histology. Both CK19 and HBME-1 were strongly positive in all nine cases of papillary thyroid carcinoma, the latter showing distinct luminal accentuation. In the non-papillary carcinomas, none showed positivity for both HBME-1 and CK19. Two of six Hurthle cell neoplasms were positive for CK19, however all were negative for HBME-1. One of nine goitrous nodules was strongly positive for HBME-1 with luminal/membranous staining, but this were negative for CK19. The sensitivity, specificity and positive predictive value of HBME-1 in distinguishing between papillary thyroid carcinoma and goitrous nodules/Hurthle cell neoplasms were found to be 100%, 92.9% and 0.9, respectively; and that of HBME-1 and CK19 combination was 100%, 100% and 1. We thus conclude that the combination of positive HBME-1 (luminal/membranous) and CK 19 (cytoplasmic) staining on cell blocks of thyroid cytologic specimens is highly discriminatory in the diagnostic workup for papillary thyroid carcinoma.     

腹膜间皮细胞在小鼠子宫内膜细胞刺激腹腔微环境中作用

目的：探讨腹腔微环境受子宫内膜细胞刺激改变中腹膜间皮细胞的作用及其对子宫内膜异位症发病机制的意义。方法： 注射小鼠子宫内膜上皮和间质细胞入小鼠腹腔，酶联免疫吸附法（ELISA）检测注射后4、24和72 h时点腹腔冲洗液细胞因子MCP-1/JE、IL-1α和IL-6蛋白表达，同步逆转录-聚合酶链式反应技术 (Real-Time RT-PCR) 检测腹膜组织 (主要含腹膜间皮细胞) 和腹腔巨噬细胞的细胞因子MCP-1/JE、IL-1 α和IL-6 mRNA表达。结果: 子宫内膜细胞刺激腹腔细胞因子蛋白含量迅速一过性升高，4 h时点为表达高峰，腹膜细胞因子基因表达与腹腔液蛋白表达同步，腹腔巨噬细胞基因表达高峰滞后于腹腔液蛋白表达。子宫内膜上皮细胞刺激腹腔炎症反应作用强于间质细胞。结论: 子宫内膜细胞刺激腹腔发生非特异性炎症反应，腹膜间皮细胞可能是其细胞因子效应的主要来源，提示腹膜在子宫内膜异位症中除作为病灶依附体外，还可能在腹腔微环境无菌性炎症反应中起重要作用。     

Combined immunohistochemistry for thyroid peroxidase, galectin-3, CK19 and HBME-1 in differential diagnosis of thyroid tumors

We evaluated some proposed molecular thyroid tumor markers: thyroid peroxidase (TPO), galectin-3, cytokeratin-19, and HBME-1, individually and in combination, by immunohistochemistry in a total of 242 archival thyroid tissue sections. The expression of each individual marker was most helpful for the diagnosis of papillary carcinoma and its follicular variant. However, none of them was sensitive and specific enough to discriminate between Hürthle adenoma and carcinoma. Galectin-3 and HBME-1 could be used as single discriminators between follicular thyroid adenoma and carcinoma, but HBME-1 is the better choice. As a single test, all analyzed tumor markers had sufficient power to predict differentiated thyroid cancer, with sensitivities ranging from 66.5% to 82.2%. The sensitivity was improved by using combinations of some proposed markers. Only two antigens, HBME-1 and TPO, had distinct predictive values for different diagnostic alternatives i.e. a sequential combination improved diagnostic accuracy between follicular thyroid adenoma and the follicular variant of papillary thyroid carcinoma to 92.6% and consequently, between overall benign and malignant thyroid tumors to 89.1%. HBME-1 is the most accurate ancillary stain in discriminating well-differentiated thyroid carcinomas from benign tumors, although the addition of TPO did improve accuracy and served as a useful confirmatory marker.     

Comparison of immunomarkers for the identification of adrenocortical cells in cytology specimens

We studied the immunoreactivity of three antibodies--A103, calretinin, and inhibin alpha in destained Papanicolaou (Pap) smears and cell-blocks of 40 fine-needle aspiration biopsy cases of adrenocortical lesions (35 cases of hyperplasia/adenoma and 5 cases of carcinoma). Five cases of carcinoma (4) and melanoma (1) metastases to the adrenal gland and five cases of renal-cell carcinoma were also included for comparison. In benign adrenocortical lesions, A103 staining was noted in 82% of the destained Pap smears and in 92% of cell-blocks. In malignant adrenocortical lesions, A103 staining was noted in 50% of the destained Pap smears and in 80% of cell-blocks. In comparison, calretinin staining was noted in 6% and 50% of destained smears and in 78% and 60% of the cell-blocks of benign and malignant adrenocortical lesions. Inhibin alpha was not positive in any of the smears and showed the lowest level of positivity in the cell-block sections, namely in 11% of the benign lesions and 25% of the malignant lesions. The sensitivity of A103 was 90% on cell-blocks and 74% on smears, that of calretinin 75% on cell-blocks and 11% on smears, and that of inhibin alpha, 13% on cell-blocks alone. The specificity of A103 was lower than the other two makers, 90% vs. 100% because of positivity in metastatic melanoma in the adrenal gland.Our data show A103 to be the immunomarker with the highest sensitivity for identifying cells of adrenocortical origin in destained Pap's smears and cell-block sections with, however, a lower specificity when compared with calretinin and inhibin alpha. Calretinin is comparable in sensitivity with A103 on cell-block sections alone and not on smears. The results of this study suggest that if metastatic melanoma in adrenal gland is not a consideration then A103 is the marker of choice for identifying cells of adrenocortical origin in the limited material available for diagnostic purposes in cytology specimens.     

TGF-β1显著上调其信号蛋白Smad2在腹膜间皮细胞中的表达

目的:探讨Smad2信号蛋白在腹膜间皮细胞中的表达及转化生长因子-β1(TGF-β1)对其表达的影响。方法:大鼠腹膜间皮细胞分别培养于不同浓度TGF-β1培养液(0、1.25、2.5、10μg/L)中,用RT-PCR和免疫组化的方法检测不同时间(0、5、15、30、60、120min)Smad2表达的水平和Smad2细胞内定位变化。结果:Smad2mRNA的表达在TGF-β1刺激后5min开始升高,呈时间依赖性,在30min达到高峰,而后逐渐减弱,在120min降至接近正常水平;Smad2mRNA表达也呈浓度依赖性,随TGF-β1浓度的增高而表达增强。磷酸化Smad2蛋白的表达和核内聚集也与mRNA表达一致,呈时间和浓度依赖性。Smad2在TGF-β1刺激下从胞浆转位至核内聚集,并在30min达高峰。结论:腹膜间皮细胞内存在Smad2的表达。TGF-β1可刺激Smad2表达上调和活化,转位至核内发挥作用,并呈浓度依赖和一定的时间依赖性。     

Carcinoma‐associated fibroblasts derive from mesothelial cells via mesothelial‐to‐mesenchymal transition in peritoneal metastasis

Peritoneal dissemination is a frequent metastatic route for cancers of the ovary and gastrointestinal tract. Tumour cells metastasize by attaching to and invading through the mesothelial cell (MC) monolayer that lines the peritoneal cavity. Metastases are influenced by carcinoma‐associated fibroblasts (CAFs), a cell population that derives from different sources. Hence, we investigated whether MCs, through mesothelial–mesenchymal transition (MMT), were a source of CAFs during peritoneal carcinomatosis and whether MMT affected the adhesion and invasion of tumour cells. Biopsies from patients with peritoneal dissemination revealed the presence of myofibroblasts expressing mesothelial markers in the proximity of carcinoma implants. Prominent new vessel formation was observed in the peritoneal areas harbouring tumour cells when compared with tumour‐free regions. The use of a mouse model of peritoneal dissemination confirmed the myofibroblast conversion of MCs and the increase in angiogenesis at places of tumour implants. Treatment of omentum MCs with conditioned media from carcinoma cell cultures resulted in phenotype changes reminiscent of MMT. Adhesion experiments demonstrated that MMT enhanced the binding of cancer cells to MCs in a β1‐integrin‐dependent manner. Scanning electron microscopy imaging showed that the enhanced adhesion was mostly due to increased cell–cell interaction and not to a mere matrix exposure. Invasion assays suggested a reciprocal stimulation of the invasive capacity of tumour cells and MCs. Our results demonstrate that CAFs can derive from mesothelial cells during peritoneal metastasis. We suggest that MMT renders the peritoneum more receptive for tumour cell attachment/invasion and contributes to secondary tumour growth by promoting its vascularization. Copyright © 2013 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.     

Pleomorphic lobular carcinoma in pleural fluid: diagnostic pitfall for atypical mesothelial cells

Pleomorphic lobular carcinoma (PLC) is a subtype of infiltrating lobular carcinoma because of its dyscohesiveness, linear infiltration pattern, and lack of membranous E-cadherin staining. However, it differs from classic lobular carcinoma because of its high-grade cytology and more aggressive clinical behavior. In breast fine-needle aspiration biopsies, PLC can be confused with invasive ductal carcinoma, particularly the apocrine variant. In this report, we illustrate how metastatic PLC in body fluid specimens shows many of the same cytomorphologic changes that occur in reactive/atypical mesothelial cells. Fortunately, the immunohistochemical staining pattern of PLC can help to distinguish it from other possible diagnoses in the differential, such as reactive/atypical mesothelial cells and other metastatic neoplasms. However, the frequent apocrine features seen in this variant of breast carcinoma can cause nonspecific immunohistochemical positivity that may make the interpretation difficult. This is the first report illustrating the cytopathology and immunohistochemical findings of pleomorphic lobular carcinoma in body cavity fluid cytology. Our case highlights the important issues and pitfalls to be aware of when making this diagnosis.     

Differentiating reactive mesothelial cells from metastatic adenocarcinoma in serous effusions: The utility of immunocytochemical panel in the differential diagnosis

Differentiating reactive mesothelial cells (RMs) from metastatic adenocarcinoma cells (MAC) in serous fluids based on cytomorphologic features alone can be very challenging. Various immunocytochemical (ICC) markers have been used to maximize the diagnostic accuracy, however, cytopathologists still encounter difficulties in effusion cytologic diagnosis. The aim of this study was to evaluate previous and recent ICC stains to identify the most sensitive and specific markers and the best panel for differentiating RM from MAC. Cell block sections from 41 MAC and 43 RM effusions cases were subjected to ICC staining for MOC‐31, BerEp4, carcinoembryonic antigen (CEA), calretinin, HBME‐1, CK5/6, and D2‐40. For the MAC cases, the sensitivity of BerEp4, MOC‐31, and CEA was 82.9, 92.6, and 17%, respectively, and the specificity was 95.3, 93, and 100%, respectively. For the RM cases, the sensitivity of calretinin, CK5/6, D2‐40, and HBME‐1 was 95.3, 27.9, 58.1, and 93%, respectively, and the specificity was 70.7, 73.1, 75.6, and 82.9%, respectively. The results show that BerEp4 and MOC‐31 are highly sensitive and specific for detecting MAC, whereas calretinin and HBME1 are highly sensitive but only modestly specific for detecting RM cases (P < 0.05). Forced entry logistic regression revealed that using MOC‐31, BerEp4, HBME‐1, and calretinin, is an excellent panel for making correct diagnosis with 97.6% sensitivity in detecting MAC and 90.7% specificity in detecting RM. We conclude that adding a panel of MOC‐31, BerEp4, calretinin, and HBME‐1 immunostains to routine cytomorphologic features can greatly enhance the diagnostic accuracy of serous effusions. Diagn. Cytopathol. 2009. © 2009 Wiley‐Liss, Inc.     

Immunocytochemical panel for distinguishing between adenocarcinomas and reactive mesothelial cells in effusion cell blocks

The aim of our study was to determine the value of a panel that consisted of one epithelial marker (MOC‐31) and two mesothelial markers (D2‐40 and calretinin) for distinguishing between reactive mesothelial cells (RMCs) and adenocarcinomas (ACs) in effusion fluids. A total of 118 cell block specimens from pleural and peritoneal effusions, including 88 ACs and 30 benign effusions with RMCs were stained with antibodies against MOC‐31, D2‐40, and calretinin. MOC‐31 membranous activity was observed in all samples from ACs, regardless of the primary tumor site. All benign effusion samples with RMCs were negative for MOC‐31. All benign effusion samples with RMCs exhibited membranous staining for D2‐40, and one AC case had focal reactivity for D2‐40. Almost all benign effusions reacted positively with calretinin. Staining was noted in both the cytoplasm and the nucleus in the majority of cases. Scattered tumor cells had weak calretinin positivity in two AC cases. Background RMCs in AC effusions were consistently positive for D2‐40 and calretinin. In general, D2‐40 identified more RMCs than calretinin. The staining combination of positive for MOC‐31 and negative for D2‐40 or calretinin were 100% specific and 99% sensitive for ACs. Our data suggest that immunohistochemical studies performed on cell blocks with MOC‐31, D2‐40, and calretinin were useful in the differentiation between ACs and RMCs. D2‐40 was a more sensitive marker for RMCs than calretinin. Diagn. Cytopathol. 2009. © 2009 Wiley‐Liss, Inc.