Comparison of immunohistochemical mesothelial biomarkers in paired biopsies and effusion cytology cell blocks from pleural mesothelioma.

OBJECTIVE: Traditionally, the diagnosis of pleural mesothelioma is based on histological material. Minimally invasive effusion cytology specimens are an alternative that, like biopsies, require ancillary analyses. Validation of immunohistochemical (IHC) analyses on cytology, including the surrogate markers for molecular alterations BAP1 and MTAP, is of interest. METHODS: IHC for eight different markers was performed on 59 paired formalin-fixed, paraffin-embedded pleural biopsies and pleural effusion cell blocks with mesothelioma. Immunoreactivity in ≥10% of tumour cells was considered positive/preserved. The concordance between histological and cytological materials was assessed. RESULTS: The overall percentage of agreement between the histological epithelioid component in 58 biopsies and paired cell blocks was 93% for calretinin, 98% for CK5, 97% for podoplanin, 90% for WT1, 86% for EMA, 100% for desmin, 91% for BAP1, and 72% for MTAP. For 11 cases with biphasic or sarcomatoid histology, the concordance between cytology and the histological sarcomatoid component was low for calretinin, CK5, and WT1 (all ≤45%). For the whole cohort, loss of both BAP1 and MTAP was seen in 40% while both markers were preserved in 11% of the biopsies for epithelioid histology. The corresponding numbers were 54% and 8%, respectively, for the paired cell blocks. CONCLUSIONS: Generally, a high concordance for IHC staining was seen between paired biopsies and pleural effusion cell blocks from mesotheliomas, but the somewhat lower agreement for WT1, EMA, and especially MTAP calls for further investigation and local quality assurance. The lower concordance for the sarcomatoid subtype for some markers may indicate biological differences.

PD-L1 Expression in Non-Small Cell Lung Cancer Specimens: Association with Clinicopathological Factors and Molecular Alterations.

Immune checkpoint inhibitors (ICI) targeting programmed cell death-1 or its ligand (PD-L1) have improved outcomes in non-small cell lung cancer (NSCLC). High tumor PD-L1 expression, detected by immunohistochemistry (IHC) typically on formalin-fixed paraffin-embedded (FFPE) histological specimens, is linked to better response. Following our previous investigation on PD-L1 in cytological samples, the aim of this study was to further explore the potential impacts of various clinicopathological and molecular factors on PD-L1 expression. Two retrospective NSCLC cohorts of 1131 and 651 specimens, respectively, were investigated for PD-L1 expression (<1%/1−49%/≥50%), sample type, sample site, histological type, and oncogenic driver status. In both cohorts, PD-L1 was positive (≥1%) in 55% of the cases. Adenocarcinomas exhibited lower PD-L1 expression than squamous cell carcinomas (p < 0.0001), while there was no difference between sample types, tumor locations, or between the two cohorts in multivariate analysis (all p ≥ 0.28). Mutational status correlated significantly with PD-L1 expression (p < 0.0001), with the highest expression for KRAS-mutated cases, the lowest for EGFR-mutated, and the KRAS/EGFR wild-type cases in between. There was no difference in PD-L1 levels between different prevalent KRAS mutations (all p ≥ 0.44), while mucinous KRAS-mutated adenocarcinomas exhibited much lower PD-L1 expression than non-mucinous (p < 0.0001). Our data indicate that cytological and histological specimens are comparable for PD-L1 evaluation. Given the impact of KRAS mutations and the mucinous growth pattern on PD-L1 expression, these factors should be further investigated in studies on ICI response.

Factors Influencing Concordance of PD-L1 Expression between Biopsies and Cytological Specimens in Non-Small Cell Lung Cancer.

PD-L1 expression assessed by immunohistochemical staining is used for the selection of immunotherapy in non-small cell lung cancer (NSCLC). Appropriate validation of PD-L1 expression in cytology specimens is important as cytology is often the only diagnostic material in NSCLC. In a previous study comprising two different cohorts of paired biopsies and cytological specimens, we found a fairly good cyto-histological correlation of PD-L1 expression in one, whereas only a moderate correlation was found in the other cohort. Therefore, that cohort with additional new cases was now further investigated for the impact of preanalytical factors on PD-L1 concordance in paired biopsies and cytological specimens. A total of 100 formalin-fixed paraffin-embedded cell blocks from 19 pleural effusions (PE), 17 bronchial brushes (BB), and 64 bronchoalveolar lavage (BAL) and concurrent matched biopsies from 80 bronchial biopsies and 20 transthoracic core biopsies from NSCLC patients were stained using the PD-L1 28-8 assay. Using the cutoffs ≥1%, ≥5%, ≥10%, and ≥50% positive tumour cells, the overall agreement between histology and cytology was 77-85% (κ 0.51-0.70) depending on the applied cutoff value. The concordance was better for BALs (κ 0.53-0.81) and BBs (κ 0.55-0.85) than for PEs (κ -0.16-0.48), while no difference was seen for different types of biopsies or histological tumour type. A high number of tumour cells (>500) in biopsies was associated with better concordance at the ≥50% cutoff. In conclusion, the study results suggest that PEs may be less suitable for evaluation of PD-L1 due to limited cyto-histological concordance, while a high amount of tumour cells in biopsies may be favourable when regarding cyto-histological PD-L1 concordance.

PD-L1 Testing in Cytological Non-Small Cell Lung Cancer Specimens: A Comparison with Biopsies and Review of the Literature.

INTRODUCTION: Programmed death-ligand 1 (PD-L1) expression is used for treatment prediction in non-small cell lung cancer (NSCLC). While cytology may be the only available material in the routine clinical setting, testing in clinical trials has mainly been based on biopsies. METHODS: We included 2 retrospective cohorts of paired, concurrently sampled, cytological specimens and biopsies. Also, the literature on PD-L1 in paired cytological/histological samples was reviewed. Focus was on the cutoff levels ≥1 and ≥50% positive tumor cells. RESULTS: Using a 3-tier scale, PD-L1 was concordant in 40/47 (85%) and 66/97 (68%) of the paired NSCLC cases in the 2 cohorts, with kappa 0.77 and 0.49, respectively. In the former cohort, all discordant cases had lower score in cytology. In both cohorts, concordance was lower in samples from different sites (e.g., biopsy from primary tumor and cytology from pleural effusion). Based on 25 published studies including about 1,700 paired cytology/histology cases, the median (range) concordance was 81-85% (62-100%) at cutoff 1% for a positive PD-L1 staining and 89% (67-100%) at cutoff 50%. CONCLUSIONS: The overall concordance of PD-L1 between cytology and biopsies is rather good but with significant variation between laboratories, which calls for local quality assurance.

Higher concordance of PD-L1 expression between biopsies and effusions in epithelioid than in nonepithelioid pleural mesothelioma.

BACKGROUND: Malignant mesothelioma (MM) is a therapy-resistant tumor, often causing an effusion. Drugs targeting the programmed cell death 1 (PD-1)/programmed cell death ligand 1 (PD-L1) pathway have shown promising results, but assessment of PD-L1 expression to select patients for therapy has mainly been performed on histologic tissue samples. In a previous study, we showed that MM effusions are suitable for PD-L1 assessment with results comparable to those reported in histologic studies, but no studies have compared PD-L1 expression in histologic and cytologic samples. METHODS: PD-L1 expression was determined immunohistochemically (clone 28-8) in 61 paired samples of effusions and biopsies from patients with pleural MM, obtained at the time of diagnosis. Only cases with >100 tumor cells were included. Membranous staining in tumor cells was considered positive at ≥1%, >5%, >10%, and >50% cutoff levels. RESULTS: Of 61 histologic samples, PD-L1 expression was found in 28 and 7 samples at ≥1% and >50% cutoffs, respectively; the corresponding figures for cytology were 21 and 5, respectively. The overall percentage agreement between histology and cytology was 69% and 84%, with a kappa (κ) of 0.36 and 0.08 at ≥1% and >50% cutoffs, respectively. The concordance between cytology and histology tended to be higher for epithelioid MM versus nonepithelioid MM at a ≥1% cutoff. PD-L1 positivity in biopsies, but not in effusions, correlated with the histologic subtype at a ≥1% cutoff. CONCLUSIONS: A moderate concordance of PD-L1 expression between biopsies and effusions from pleural MM, especially for the epithelioid subtype, indicates biological differences between the 2 types of specimens. Cytology and histology may be complementary.

Immune effector monocyte-neutrophil cooperation induced by the primary tumor prevents metastatic progression of breast cancer.

Metastatic behavior varies significantly among breast cancers. Mechanisms explaining why the majority of breast cancer patients never develop metastatic outgrowth are largely lacking but could underlie the development of novel immunotherapeutic target molecules. Here we show interplay between nonmetastatic primary breast cancer and innate immune response, acting together to control metastatic progression. The primary tumor systemically recruits IFNγ-producing immune effector monocytes to the lung. IFNγ up-regulates Tmem173/STING in neutrophils and enhances their killing capacity. The immune effector monocytes and tumoricidal neutrophils target disseminated tumor cells in the lungs, preventing metastatic outgrowth. Importantly, our findings could underlie the development of immunotherapeutic target molecules that augment the function of immune effector monocytes and neutrophils.

Determination of PD-L1 expression in effusions from mesothelioma by immuno-cytochemical staining.

BACKGROUND: Malignant mesothelioma (MM) is an aggressive, fatal tumor. Current therapeutic options only marginally improve survival. Programmed cell death ligand 1 (PD-L1) is a dominant mediator of immunosuppression, binding to programmed cell death 1 (PD-1). PD-L1 is up-regulated in cancer cells, and the PD-1/PD-L1 pathway plays a critical role in tumor immune evasion, thus providing a target for antitumor therapy. Further, a correlation between PD-L1 expression and prognosis has been reported. Studies performed on histological material have revealed expression of PD-L1 in MM, but no study has been performed on MM effusions thus far. METHODS: PD-L1 expression was determined by a commercially available antibody (clone 28-8) in 74 formalin-fixed, paraffin-embedded cell blocks from body effusions obtained at diagnosis from patients with MM. The presence of MM cells was confirmed with CK5/6, calretinin, and EMA and the admixture of macrophages was assessed with CD68. Only cases containing more than 100 tumor cells were assessed. Membranous staining in tumor cells was considered positive. Survival time was calculated from the appearance of the first malignant effusion until death. RESULTS: Reactivity was observed in 23 of 61 (38%) of cases and was classified as ≥1%-5% (n = 9 cases), >5%-10% (n = 4 cases), >10%-50% (n = 4 cases), and >50% (n = 6 cases) positive cells. Survival times did not differ significantly between patients with PD-L1-positive and PD-L1-negative tumors. CONCLUSION: MM effusions are suitable for immune-cytochemical assessment of PD-L1 expression in malignant cells and the results are similar to those reported for histological specimens. Cancer Cytopathol 2017;125:908-17. © 2017 American Cancer Society.

Guidelines for cytopathologic diagnosis of epithelioid and mixed type malignant mesothelioma. Complementary statement from the International Mesothelioma Interest Group, also endorsed by the International Academy of Cytology and the Papanicolaou Society of Cytopathology.

To provide practical guidelines for the cytopathologic diagnosis of malignant mesothelioma (MM). Cytopathologists involved in the International Mesothelioma Interest Group (IMIG) and the International Academy of Cytology (IAC), who have an interest in the field contributed to this update. Reference material includes peer-reviewed publications and textbooks. This article is the result of discussions during and after the IMIG 2012 conference in Boston, followed by thorough discussions during the 2013 IAC meeting in Paris. Additional contributions have been obtained from cytopathologists and scientists, who could not attend these meetings, with final discussions and input during the IMIG 2014 conference in cape town. During the previous IMIG biennial meetings, thorough discussions have resulted in published guidelines for the pathologic diagnosis of MM. However, previous recommendations have stated that the diagnosis of MM should be based on histological material only.[12] Accumulating evidence now indicates that the cytological diagnosis of MM supported by ancillary techniques is as reliable as that based on histopathology, although the sensitivity with cytology may be somewhat lower.[345] Recognizing that noninvasive diagnostic modalities benefit both the patient and the health system, future recommendations should include cytology as an accepted method for the diagnosis of this malignancy.[67] The article describes the consensus of opinions of the authors on how cytology together with ancillary testing can be used to establish a reliable diagnosis of MM.

Guidelines for the cytopathologic diagnosis of epithelioid and mixed-type malignant mesothelioma: Complementary Statement from the International Mesothelioma Interest Group, Also Endorsed by the International Academy of Cytology and the Papanicolaou Society of Cytopathology.

OBJECTIVE: To provide practical guidelines for the cytopathologic diagnosis of malignant mesothelioma. DATA SOURCES: Cytopathologists with an interest in the field involved in the International Mesothelioma Interest Group (IMIG) and the International Academy of Cytology (IAC) contributed to this update. Reference material includes peer-reviewed publications and textbooks. RATIONALE: This article is the result of discussions during and after the IMIG 2012 conference in Boston, followed by thorough discussions during the 2013 IAC meeting in Paris. Additional contributions have been obtained from cytopathologists and scientists who could not attend these meetings, with final discussions and input during the IMIG 2014 conference in Cape Town.

Guidelines for the cytopathologic diagnosis of epithelioid and mixed-type malignant mesothelioma. Complementary statement from the International Mesothelioma Interest Group, also endorsed by the International Academy of Cytology and the Papanicolaou Society of Cytopathology.

OBJECTIVE: To provide practical guidelines for the cytopathologic diagnosis of malignant mesothelioma. DATA SOURCES: Cytopathologists with an interest in the field involved in the International Mesothelioma Interest Group (IMIG) and the International Academy of Cytology (IAC) contributed to this update. Reference material includes peer-reviewed publications and textbooks. RATIONALE: This article is the result of discussions during and after the IMIG 2012 conference in Boston, followed by thorough discussions during the 2013 IAC meeting in Paris. Additional contributions have been obtained from cytopathologists and scientists who could not attend these meetings, with final discussions and input during the IMIG 2014 conference in Cape Town.

Telomerase activity analyzed with TRAP in situ provides additional information in effusions remaining equivocal after immunocytochemistry and hyaluronan analysis.

Cytology is central in the diagnosis of malignancy in effusions. Ancillary techniques, mainly immunocytochemistry, have considerably improved the sensitivity but some 10% of all cases remain equivocal and require the addition of new diagnostic modalities. We have previously shown that strong nuclear telomerase activity determined with Telomere Repeat Amplification Protocol (TRAP) in situ is specific for malignant cells and could be a candidate for an additional test. Thirty effusions remaining diagnostically equivocal after the use of immunocytochemistry and the determination of the hyaluronan content were reviewed and their TRAP in situ reactivity was related to the definitive diagnoses based on all available data. There were seven effusions from patients with definitive benign diagnoses and 23 effusions from patients with definitive malignant diagnoses. Strong telomerase activity was seen only in effusions from patients with definitive malignant diagnosis, all effusions from patients with benign disease lacking strong telomerase activity, whereas eight of the malignant cases, including three cases of epithelial mesothelioma, showed strong reactivity. Strong nuclear TRAP in situ reactivity was demonstrated only in effusions from patients with verified malignant disease. Although the study is small, it suggests that TRAP in situ activity provides diagnostic information in about one-third of effusions remaining cytologically equivocal after the use of current ancillary techniques. The most striking diagnostic improvement appears to be gained in epithelial mesotheliomas.

Liquid-based cytology using CytoRich Red/Tripath is diagnostically equivalent to conventional smears for bronchial washings and brushings and reduces the cost.

A split sample study was performed on 109 bronchial brushings and washings and evaluated from conventional slides (CS) and CytoRich Red/Tripath preparations (CRR/Tripath). Unassessable bronchial washings were significantly more frequent in CS (5 vs. 0), but as all brushings were assessable with both methods, no overall diagnostic advantage was found. CS and CRR/Tripath gave discordant diagnoses in one case with a final benign diagnosis and in six cases with final malignant diagnoses. In the benign case, atypia was assessed in CS. In the malignant cases, suspected malignancy was found in one CRR/Tripath and one CS, atypia vs. benign assessment was also balanced, with three atypias in CRR/Tripath and two in CS. The better preserved cells in CRR/Tripath facilitated correct diagnosis in some cases, but might also lead to false positive diagnoses. In small cell carcinomas diagnostic hints such as smearing and moulding were less pronounced in CRR/Tripath but this did not affect the diagnostic accuracy. Overall, the diagnostic performance with CRR/Tripath was at least as good as with conventional slides, although statistically no difference could be seen. The number of slides and screening time, and thereby cost was significantly reduced with CRR/Tripath, thus the liquid-based method is preferred for bronchial washings and brushings.

Preparation of DNA from cytological material: effects of fixation, staining, and mounting medium on DNA yield and quality.

BACKGROUND: Personalized oncology requires molecular analysis of tumor cells. Several studies have demonstrated that cytological material is suitable for DNA analysis, but to the authors' knowledge there are no systematic studies comparing how the yield and quality of extracted DNA is affected by the various techniques used for the preparation of cytological material. METHODS: DNA yield and quality were compared using cultured human lung cancer cells subjected to different preparation techniques used in routine cytology, including fixation, mounting medium, and staining. The results were compared with the outcome of epidermal growth factor receptor (EGFR) genotyping of 66 clinical cytological samples using the same DNA preparation protocol. RESULTS: All tested protocol combinations resulted in fragment lengths of at least 388 base pairs. The mounting agent EcoMount resulted in higher yields than traditional xylene-based medium. Spray and ethanol fixation resulted in both a higher yield and better DNA quality than air drying. In liquid-based cytology (LBC) methods, CytoLyt solution resulted in a 5-fold higher yield than CytoRich Red. Papanicolaou staining provided twice the yield of hematoxylin and eosin staining in both liquid-based preparations. Genotyping outcome and quality control values from the clinical EGFR genotyping demonstrated a sufficient amount and amplifiability of DNA in both spray-fixed and air-dried cytological samples. CONCLUSIONS: Reliable clinical genotyping can be performed using all tested methods. However, in the cell line experiments, spray- or ethanol-fixed, Papanicolaou-stained slides provided the best results in terms of yield and fragment length. In LBC, the DNA recovery efficiency of the preserving medium may differ considerably, which should be taken into consideration when introducing LBC. Cancer (Cancer Cytopathol) 2013;121:344-353. © 2013 American Cancer Society.

Possibility of mixed progenitor cells in sea star arm regeneration.

In contrast to most vertebrates, invertebrate deuterostome echinoderms, such as the sea star Asterias rubens, undergo regeneration of lost body parts. The current hypothesis suggests that differentiated cells are the main source for regenerating arm in sea stars, but there is little information regarding the origin and identity of these cells. Here, we show that several organs distant to the regenerating arm responded by proliferation, most significantly in the coelomic epithelium and larger cells of the pyloric caeca. Analyzing markers for proliferating cells and parameters indicating cell ageing, such as levels of DNA damage, pigment, and lipofuscin contents as well as telomere length and telomerase activity, we suggest that cells contributing to the new arm likely originate from progenitors rather than differentiated cells. This is the first study showing that cells of mixed origin may be recruited from more distant sources of stem/progenitor cells in a sea star, and the first described indication of a role for pyloric caeca in arm regeneration. Data on growth rate during arm regeneration further indicate that regeneration is at the expense of whole animal growth. We propose a new working hypothesis for arm regeneration in sea stars involving four phases: wound healing by coelomocytes, migration of distant progenitor cells of mixed origin including from pyloric caeca, proliferation in these organs to compensate for cell loss, and finally, local proliferation in the regenerating arm.

Podoplanin is a useful marker for identifying mesothelioma in malignant effusions.

The diagnosis of malignant mesothelioma in serosal effusions continues to be a major challenge because some of its cytomorphological features closely resemble adenocarcinomas. Immunohistochemistry is a valuable tool in the differentiation of epithelioid mesothelioma from metastatic adenocarcinomas. However, no single antibody has demonstrated absolute sensitivity or specificity. In this study, we evaluated the value of immunostaining pattern for podoplanin to differentiate mesothelioma from adenocarcinomas of various origins.Cell blocks from previously collected paraffin-embedded cell blocks of 86 effusions (18 mesothelioma, 35 reactive mesothelium, 9 breast adenocarcinoma, 14 ovarian adenocarcinoma, and 10 lung adenocarcinoma) were retrieved from the file of the Department of Pathology at University of Michigan and Lund University in Sweden and were used for the study. Slides prepared from the cell blocks were stained for podoplanin. The percentage of immunostained cells was recorded as follows: 1+ (5-25%), 2+ (26-50%), and 3+ (>50%). A stain result involving <5% of cells was considered negative. The intensity of positive results was evaluated as strong, moderate, or weak.Podoplanin is expressed in 94% of malignant mesothelioma cases (17/18), 97% (30/31) of cases of reactive mesothelial, 0% of lung adenocarcinoma cases (0/9), 0% of breast adenocarcinoma (0/9), and 7% of ovarian adenocarcinoma (1/14). All positive cases of malignant mesothelioma and reactive mesothelium showed strong membranous reactivity to podoplanin. The one positive case of ovarian adenocarcinoma showed a weak membranous podoplanin immunostaining.On the basis of our results and published data, we believe that membranous podoplanin immunoreactivity, in conjunction with calretinin, would be more specific than CK5/6 and WT-1 in differentiating epithelioid malignant mesothelioma from adenocarcinoma of the lung, breast, and ovary.

Telomerase activity in effusions: a comparison between telomere repeat amplification protocol in situ and conventional telomere repeat amplification protocol assay.

CONTEXT: We previously found telomere repeat amplification protocol (TRAP) in situ helpful in the diagnosis of malignancy in effusions, whereas varying sensitivities and specificities for malignancy were reported by investigators using extract-based TRAP. OBJECTIVE: To compare the 2 methods and to elucidate the discrepancies between them. DESIGN: Twenty-three effusions were analyzed. Telomerase activity of whole cell lysate was measured with a Telo TAGGG telomerase polymerase chain reaction ELISA PLUS kit with modifications to exclude polymerase chain reaction inhibitors. TRAP in situ was performed on cytospins. An estimate of total TRAP activity in the specimen was made based on the amount of positive cells, their fluorescence intensity, and the proportion of different cell types in the specimen. The estimate was compared with the level of telomerase activity in cell lysate-based TRAP. RESULTS: TRAP in situ: Thirteen of 14 malignant cases and 2 of 2 equivocal cases showed moderate/strong reactivity. Five of 7 benign effusions were negative; in 2 of 7, mesothelial cells showed weak reactivity. Cell lysate-based TRAP assay: In 4 cases no internal standard was detected, indicating the presence of polymerase chain reaction inhibitors. The relative telomerase activities were 33.1 to 72.7 with a considerable overlap between malignant (48 +/- 9, mean +/- SD) and benign (43 +/- 9) cases. CONCLUSIONS: The TRAP in situ results correlated to final diagnoses, whereas the cell lysate-based TRAP assay did not differentiate between malignant and benign cases. The varying proportions of positive cells and the variation in fluorescence intensity in the TRAP in situ slides explained some of the discrepancies. The problems encountered with TRAP performed on cell lysates are partly overcome using TRAP in situ.

CK5/6 in effusions: no difference between mesothelioma and pulmonary and nonpulmonary adenocarcinoma.

OBJECTIVE: To test the performance of CK5/6 for the differentiation between mesothelioma, adenocarcinoma and benign mesothelia/proliferations in effusion cytology. STUDY DESIGN: CKS/6 immunocytochemistry was applied to ethanol-fixed cytospin preparations from 74 benign and malignant effusions. RESULTS: Reactivity was seen in 7 of 8 mesotheliomas and in 9 of 11 benign mesothelial proliferations but also in 11 of l7 pulmonary adenocarcinomas and in 12 of 31 adenocarcinomas of nonpulmonary origin. Reactivity was also found in 3 of 5 non-small cell lung carcinomas and 1 of 1 squamous carcinoma. CONCLUSION: CK5/6 reactivity was found in a considerable proportion of metastatic adenocarcinomas of pulmonary and nonpulmonary origin. The high reactivity rate in pulmonary adenocarcinomas disagrees with the results obtained with histologic sections from solid tumor tissue, and CK5/6 seems to be of very limited value as an additional marker in effusion cytology.

Comparison of NCL-hTERT antibody reactivity and telomere repeat amplification protocol in situ in effusions.

OBJECTIVE: To compare the performances of 2 methods, telomerase repeat amplification protocol (TRAP) in situ and antibodies to the hTERT protein, in assessing telomerase activity. STUDY DESIGN: TRAP in situ and immunohistochemistry with a commercial antibody (NCL-hTERT) was performed on 54 body cavity effusions. The results were compared and correlated to diagnosis. RESULTS: Thirty-four effusions from patients with verified malignant disease contained cytologically malignant cells. Both methods were positive in 33 of the cases, whereas only hTERT was positive in 1 case. Twenty effusions, all containing mesothelial cells, came from patients with benign conditions. In 2 fluids atypical, hyperplastic mesothelial cells were both TRAP in situ and hTERT positive. All remaining 18 fluids were TRAP in situ negative, whereas 12 of 18 were hTERT positive. Thus the results of TRAP in situ and hTERT immunohistochemistry disagreed in 1 of 34 (3%) malignant and 12 of 20 (60%) benign cases. CONCLUSION: The sensitivities for malignancy were similar for TRAP in situ and hTERT immunohistochemistry. The specificity of the applied hTERT antibody was significantly lower, due to hTERT reactivity in mesothelial cells.

Lower proliferation rate in metastatic effusion mesothelial cells than in benign effusions.

OBJECTIVE: To determine the proliferation rates of mesothelial cells in metastatic and benign effusions. STUDY DESIGN: Immunohistochemistry was performed on formalin-fixed pellets from 16 malignant and 9 benign clinical effusions. Dual staining with antibodies against Ki-67 (MIB-1) and desmin was applied to all effusions to differentiate between benign mesothelial cells and malignant cells, and the proportions of desmin+/Ki-67+ and desmin+/Ki-67- cells were calculated. RESULTS: In 7 malignant effusions no proliferating mesothelial cells were found, whereas some rate of proliferation could always be demonstrated in mesothelial cells in the benign effusions. Further, the median proportions of proliferating cells, malignant 2% vs. benign 11%, differed significantly. CONCLUSIONS: To our knowledge this finding has not been previously described, and it may have implications for both cytologic diagnosis and the understanding of tumor biology and the interaction between tumor cells and mesothelial cells.