Immunocytochemistry of cytology specimens for predictive biomarkers in lung cancer

Practical issues related to immunocytochemistry on cytological smears: Tips and recommendations

OBJECTIVE

Immunocytochemistry (ICC) is essential for enhancing diagnostic accuracy and identifying markers for diagnosis, prognosis and targeted therapies. While cell blocks (CBs) are preferred for standardization and optimized staining, cytological smears are an alternative when CBs are unavailable. However, the literature on ICC protocols for smears is sparse. This review addresses preparation, fixation and protocols for nuclear and cytoplasmic antibodies on smears, drawing from our laboratory's experience.

METHODS

We reviewed procedures for ICC on cytological smears using existing literature and practical insights from our laboratory.

RESULTS

Commercially available antibodies were found to be reliable for ICC on smears if specimens are properly prepared and fixed. Protocols developed in our laboratory maintained antigenicity and provided clear staining results.

CONCLUSIONS

Although ICC on CBs is the gold standard for standardization, cytological smears are a viable alternative when CBs are unavailable. Success in ICC on smears depends on proper preparation and fixation. This review offers practical protocols and insights to help laboratories optimize ICC on cytological smears. Further research and standardization are necessary to enhance reproducibility and reliability of ICC on smears. The practical information provided is based on personal experience in our laboratory.

Utility of Wnt family member 9b (Wnt9b) immunohistochemistry in the cytologic diagnosis of metastatic breast carcinoma

Wnt family member 9b (Wnt9b) has been demonstrated as a valuable marker for breast cancer diagnosis in surgical pathology. In this study, we examined the utility of Wnt9b in diagnosing metastatic breast carcinoma in cytology samples. Cell blocks from fine needle aspirations (FNA) and fluid specimens of 96 metastatic breast carcinomas and 123 primary and metastatic non-breast neoplasms from various organ systems were evaluated by Wnt9b and GATA3 immunohistochemistry (IHC). Wnt9b and GATA3 were positive in 81.3% and 92.7% of metastatic breast carcinomas, respectively. Conversely, 93.5% and 90.0% of non-breast, non-urothelial carcinomas were negative for Wnt9b and GATA3, respectively. Wnt9b expression was positive in rare gastrointestinal, gynecological, lung, pancreas, and salivary gland tumors. All twenty-eight urothelial carcinomas were negative for Wnt9b, while twenty-six (92.9%) were positive for GATA3. Wnt9b was slightly less sensitive but more specific than GATA3 in diagnosing metastatic breast cancer in cytology samples. Particularly, Wnt9b shows higher specificity in differentiating breast and urothelial primaries. The combined use of Wnt9b and GATA3 may increase diagnostic accuracy.

Quality Assurance in Immunocytochemistry: A Review and Practical Considerations

BACKGROUND

Cytological samples play a critical role in diagnosing advanced-stage tumors and those arising in difficult-to-reach anatomical sites such as the pancreatobiliary tract, lung, thyroid, suprarenal, pelvis, and others such as salivary glands. These samples are often the only available material for accurate diagnosis and for performing ancillary studies, such as immunocytochemistry (ICC) or the detection of molecular biomarkers.

SUMMARY

While the use of immunohistochemistry is well established and standardized on formalin-fixed-paraffin-embedded histological tissue, in cytological samples, it presents unique challenges. Methods used for obtaining and processing these specimens are complex and are not standardized among laboratories. Moreover, there is also diversity in the types of cytological samples potentially suitable for ICC.

KEY MESSAGES

This review explores the current landscape of ICC practices in European and North American laboratories, highlighting variability in methods and the need for standardization to ensure reliable results and reproducibility of ICC on cytological specimens.

The impact of different fixatives on immunostaining of lung adenocarcinomas in pleural effusion cell blocks

BACKGROUND

Cell blocks (CBs) are widely used for biomarker analyses such as immunostaining. Although immunohistochemistry on formalin-fixed paraffin-embedded tissues is standardized, there are multiple preparation methods and fixatives for cytology. Our objective was to investigate the effect of different common fixatives on the immunoreactivity of pleural effusion CBs with metastatic lung adenocarcinomas.

METHODS

This prospective study included 24 malignant pleural effusions from different patients with lung adenocarcinoma. From each case, four identical CBs were fixed in 10% neutral buffered formalin, PreservCyt, CytoLyt, and CytoRich Red (only 17 of the cases), respectively. Samples containing <100 malignant cells were excluded. All CBs were stained with thyroid transcription factor 1 (TTF-1; clones 8G7G3/1 and SPT24), napsin A, claudin 4, CEA, CK7, and epithelial cell adhesion molecule (EpCAM; clones BS14, Ber-Ep4, and MOC-31). The fraction and intensity of stained cells were evaluated.

RESULTS

Of the investigated markers, a significant difference in staining proportion was seen for TTF-1 clone 8G7G3/1 and EpCAM clone MOC-31, especially with cases being negative in CytoLyt (33.3% and 83.3% positive, respectively) and PreservCyt (62.5% and 83.3%) whereas being positive in CytoRich Red (76.5% and 94.1%) and formalin (both 95.8%). A significantly weaker intensity of staining was seen for all alcohol-based fixatives compared to formalin for TTF-1 clone 8G7G3/1, napsin A, and EpCAM clone MOC-31, whereas EpCAM clone Ber-Ep4 was significantly weaker only in PreservCyt compared with formalin.

CONCLUSIONS

Immunocytochemical expression and concordance with formalin-fixed CBs differ depending on the used fixative as well as the antibody and clone, warranting investigation of the reliability of each biomarker for non-formalin-fixed cytology.

Quality of cell blocks prepared from residual pleural effusion and bronchial washing samples for immunocytochemistry

INTRODUCTION

Cell blocks (CBs) enable the long-term preservation of cytological samples. The aim of this study was to analyse the quality of CBs prepared from leftover fluid from lung adenocarcinoma pleural effusion samples and residual bronchial washing sediment for immunocytochemistry.

METHODS

The residual part of 455 lung adenocarcinoma pleural effusion samples and sediment from 384 bronchial washing samples were used to prepare CBs following the agarose method. The quality of CBs was evaluated based on the quantity of malignant cells in haematoxylin and eosin-stained slides and interpreted as optimal or insufficient for immunocytochemistry. Immunocytochemistry on CBs was performed using the Dako EnVision™ FLEX detection visualisation system. The CB results for TTF-1, ALK, and PD-L1 immunocytochemistry were compared with the corresponding cytological smears.

RESULTS

Among all CBs, 202 (44.4%) from leftover pleural effusion fluid and 85 (22.1%) from residual bronchial washing sediment had an optimal number of lung adenocarcinoma cells. Eight pleural effusion CBs were stained for TTF-1. Four pleural effusion and two bronchial washing CBs were stained for ALK and PD-L1. All tested pleural effusion CBs were confirmed positive for TTF-1 and negative for ALK. The PD-L1 tumour proportion score (TPS) was ≥ 50% in two pleural effusions. ALK was confirmed negative in bronchial washing CBs. One bronchial washing CB was interpreted as PD-L1-negative while the corresponding smear was positive (TPS ≥1%; 2%).

CONCLUSION

The CB results of TTF-1, ALK, and PD-L1 corresponded to the findings for the smears. The inclusion of CBs prepared from leftover fluid from pleural effusion samples and residual bronchial washing sediment in routine cytological practice could provide a source of high-quality material for immunocytochemistry in addition to smears and cytospins.

Molecular/biomarker testing in lung cytology: A practical approach

The increasing comprehension of molecular mechanisms underlying lung cancer and the discovery of targetable genomic alterations has dramatically change the pathological approach to lung cancer, especially non-small cell lung cancer (NSCLC). This unstoppable knowledge has taken pathologists to the leading front on lung cancer management. This is especially relevant in the world of cytopathology where "doing more with less" is a daily challenge. Nowadays with a growing number of predictive biomarkers needed to manage patients with NSCLC, there has been a paradigm shift in care and handling of diagnostic samples. One of the main emphasis and interest relies on the utilization of cytologic samples and small biopsies for not only diagnostic purposes but also for ancillary testing. Moreover, lung cytopathology is in continuous evolutions with implementation of new diagnostic techniques, new tools, and facing new challenges. The goal of this paper will be to provide the reader with the necessary concepts than can be used to exploit the cytological samples in order to use these samples for comprehensive diagnosis and relevant ancillary testing purposes.

Recommendations for optimizing the use of cytology in the diagnosis and management of patients with lung cancer

Non-small cell lung cancer (NSCLC) is one of the oncological entities with the greatest evolution in molecular diagnosis due to the large number of diagnostic biomarkers and new treatments approved by international regulatory agencies. An accurate, early diagnosis using the least amount of tissue is the goal for the establishing and developing precision medicine for these patients. Rapid on-site evaluation (ROSE) provides cytological samples of optimal quantity and quality for a complete diagnosis of NSCLC. The usefulness of cytological samples has been demonstrated, not only for massive parallel sequencing but also for the quantification of the expression of programmed death-ligand 1 (PD-L1) and tumour mutational burden (TMB). Pre-analytical, analytical, and post-analytical recommendations are made for the management and appropriate use of cytological samples in order to obtain all the information necessary for the diagnosis and treatment of patients with NSCLC according to current quality parameters.

Tissue Microarray from Cell Block Material (cbTMA)—An Additional Shot for Cytology in the Predictive Pathology Era: The PD-L1 Experience

Generally, predictive biomarker tests are clinically validated on histological formalin-fixed, paraffin-embedded (FFPE) samples. In addition to FFPE samples, cytological samples have also emerged as a useful approach to detect predictive biomarkers. However, as of today, despite the promising results reported in the recent literature, their full implementation in routine clinical practice is still lagging owing to a lack of standardized preparatory protocols, challenging assessments of cyto-histological correlation, and variable inter-observer agreement. The aim of this report was to explore the possibility of implementing a large-scale validation of predictive biomarker testing on cytological material. To this aim, we evaluated the technical feasibility of PD-L1 assessment on a cell block (CB)-derived tissue microarray (cbTMA). Consecutive and unselected CBs prepared from metastatic lymph node fine-needle cytology (FNC) samples were retrospectively collected and used for TMA construction. PD-L1 immunohistochemistry (IHC) was carried out on cbTMA sections with the companion diagnostic kit SP263 assay. TMA contained 33 CB-derived cores. A total of 20 sections were hematoxylin and eosin (H&E) stained. Overall, 29 (88%) samples were visible at least in one H&E-stained slide. Four cases out of five sections stained with the SP263 assay (4/29, 13.8%) showed PD-L1 positivity in neoplastic and/or immune cells; remarkably, no unspecific background was observed. Although our study was based on a limited and non-selected series, our findings do provide proof of concept for the use of cbTMA in predictive biomarker testing on cytological material in large-scale post-clinical trial validation studies, multicenter studies, and quality control programs.

Feasibility of using digital confocal microscopy for cytopathological examination in clinical practice

Optical imaging modalities are emerging as digital microscopy tools for tissue examination. The investigation of these techniques for potential applications in anatomic pathology practice has focused primarily on surgical pathology and has not included cytopathological specimens. We evaluated the feasibility of using digital confocal microscopy (CM) to examine cytopathological specimens. Smears and cell suspensions collected in RPMI solution were prepared from tissue scrapes obtained from surgical resections of breast, lung, liver, and kidney. Air-dried smears and cell pellets obtained from centrifugation of the cell suspensions were stained with 0.6 mM acridine orange and imaged with a CM platform. After completion of imaging, the smears were stained with Diff-Quik (DQ), and cell pellets were routinely processed, embedded in paraffin wax, cut, and stained with hematoxylin and eosin (H&E). We evaluated the mean time to acquire digital CM images; quality of images based on the extent of tissue recognition (0%, grade 0; 1-19%, grade 1; 20-50%, grade 2; >50%, grade 3); comparison of images with DQ- and H&E-stained specimens; and ability to make specific diagnoses. We imaged 91 smears and 52 cell pellets and acquired digital CM images within 2-3 min, with 92% and 88% of images, respectively, from smears and cell pellets showing grade 3 quality. On the basis of CM images, 8 smears (9%) and 7 cell pellets (14%) were categorized as benign, and 83 (91%) and 45 (88%), respectively, as malignant. Specific diagnoses were made by using digital CM images of smears and cell pellets that matched accurately with corresponding DQ- and H&E-stained preparations. The results of our first feasibility study clearly indicated the utility of CM as a next-generation digital microscopy tool for evaluating cytology specimens. Prospective clinical studies are warranted for validating our findings for potential incorporation into cytopathological clinical practice.

Technical aspects of the use of cytopathological specimens for diagnosis and predictive testing in malignant epithelial neoplasms of the lung

Lung cancer is a leading cause of cancer mortality worldwide but recent years have seen a rapidly rising proportion of cases of advanced non-small cell carcinoma amenable to increasingly targeted therapy, initially based on the differential response to systemic treatment of tumours of squamous or glandular differentiation. In two-thirds of the cases, where patients present with advanced disease, both primary pathological diagnosis and biomarker testing is based on small biopsies and cytopathological specimens. The framework of this article is an overview of the technical aspect of each stage of the specimen pathway with emphasis on maximising potential for success when using small cytology samples. It brings together the current literature addressing pre-analytical and analytical aspects of specimen acquisition, performing rapid onsite evaluation, and undertaking diagnostic and predictive testing using immunocytochemistry and molecular platforms. The advantages and drawbacks of performing analysis on cell block and non-cell block specimen preparations is discussed.

What Is New in Biomarker Testing at Diagnosis of Advanced Non-Squamous Non-Small Cell Lung Carcinoma? Implications for Cytology and Liquid Biopsy

The discovery and clinical validation of biomarkers predictive of the response of non-squamous non-small-cell lung carcinomas (NS-NSCLC) to therapeutic strategies continue to provide new data. The evaluation of novel treatments is based on molecular analyses aimed at determining their efficacy. These tests are increasing in number, but the tissue specimens are smaller and smaller and/or can have few tumor cells. Indeed, in addition to tissue samples, complementary cytological and/or blood samples can also give access to these biomarkers. To date, it is recommended and necessary to look for the status of five genomic molecular biomarkers (EGFR, ALK, ROS1, BRAFV600, NTRK) and of a protein biomarker (PD-L1). However, the short- and more or less long-term emergence of new targeted treatments of genomic alterations on RET and MET, but also on others’ genomic alteration, notably on KRAS, HER2, NRG1, SMARCA4, and NUT, have made cellular and blood samples essential for molecular testing. The aim of this review is to present the interest in using cytological and/or liquid biopsies as complementary biological material, or as an alternative to tissue specimens, for detection at diagnosis of new predictive biomarkers of NS-NSCLC.

Immunocytochemistry for diagnostic cytopathology-A practical guide

Cytological specimens, which are obtained by minimally invasive methods, are an excellent source of diagnostic material. Sometimes they are the only material available for diagnosis as well as for prognostic/predictive markers. When cytomorphology is not straightforward, ancillary tests may be required for a definitive diagnosis to guide clinical management. Immunocytochemistry (ICC) is the most common and practical ancillary tool used to reach a diagnosis when cytomorphology is equivocal, to differentiate entities with overlapping morphological features, and to determine the cell lineage and the site of origin of a metastatic neoplasm. Numerous immunomarkers are available, and some are expressed in multiple neoplasms. To rule out entities within a differential diagnosis, the use of more than one marker, sometimes panels, is necessary. ICC panels for diagnostic purposes should be customised based on the clinical context and cytomorphology, and the markers should be used judiciously to preserve material for additional tests for targeted therapies in the appropriate setting. This review offers a practical guide for the use of ICC for diagnostic cytopathology, covering the most commonly encountered non-hematolymphoid diagnostic scenarios in various body sites.

PD-L1 in Cytological Samples: A Review and a Practical Approach

With a growing number of predictive biomarkers needed to manage patients with non-small cell lung cancer (NSCLC), there has been a paradigm shift in care and handling of diagnostic samples. Among the various testing methods, immunohistochemistry (IHC) is the most cost- effective and widely available. Furthermore, over the past decade immunotherapy has emerged as one of the most promising cancer treatments. In this scenario IHC is the most used testing method available for PDL-1/PD1 immunotherapy. Several monoclonal antibodies targeting programmed death 1 (PD-1)/programmed death ligand-1 (PD-L1) pathways have been integrated into standard-of-care treatments of a wide range of cancer types, once provided evidence of PD-L1 expression in tumor cells by immunohistochemistry (IHC). Since currently available PD-L1 assays have been developed on formalin-fixed paraffin embedded (FFPE) histological specimens, a growing body of research is being dedicated to confirm the feasibility of applying PDL-1 assays also to cytological samples. Albeit promising results have been reported, several important issues still need to be addressed. Among these are the type of cytological samples, pre-analytical issues, cyto-histological correlation, and inter-observer agreement. This review briefly summarizes the knowledge of the role of cytopathology in the analysis of PD-L1 by immunocytochemistry (ICC) and future directions of cytopathology in the immunotherapy setting.

PD-L1 and beyond: Immuno-oncology in cytopathology

Over the past decade, immunotherapy has emerged as one of the most promising cancer treatments. Several monoclonal antibodies targeting the programmed death 1 (PD-1)/ programmed death ligand-1 (PD-L1) pathway have been integrated into standard-of-care treatments for a wide range of cancer types. Although all the available PD-L1 immunohistochemistry (IHC) assays have been developed on formalin-fixed histological specimens, a growing body of research has recently suggested the feasibility of PD-L1 testing on cytological samples. Although promising results have been reported, several important issues still need to be addressed. Among these are pre-analytical issues, cyto-hystological correlation, and inter-observer agreement. This review will briefly summarise the knowledge gaps and future directions of cytopathology in the immuno-oncology scenario.

Multiplex immune protein profiling of fine-needle aspirates from patients with non-small-cell lung cancer reveals signatures associated with PD-L1 expression and tumor stage

Biomarker signatures identified through minimally invasive procedures already at diagnosis of non‐small‐cell lung cancer (NSCLC) could help to guide treatment with immune checkpoint inhibitors (ICI). Here, we performed multiplex profiling of immune‐related proteins in fine‐needle aspirate (FNA) samples of thoracic lesions from patients with NSCLC to assess PD‐L1 expression and identify related protein signatures. Transthoracic FNA samples from 14 patients were subjected to multiplex antibody‐based profiling by proximity extension assay (PEA). PEA profiling employed protein panels relevant to immune and tumor signaling and was followed by Qlucore^® Omics Explorer analysis. All lesions analyzed were NSCLC adenocarcinomas, and PEA profiles could be used to monitor 163 proteins in all but one sample. Multiple key immune signaling components (including CD73, granzyme A, and chemokines CCL3 and CCL23) were identified and expression of several of these proteins (e.g., CCL3 and CCL23) correlated to PD‐L1 expression. We also found EphA2, a marker previously linked to inferior NSCLC prognosis, to correlate to PD‐L1 expression. Our identified protein signatures related to stage included, among others, CXCL10 and IL12RB1. We conclude that transthoracic FNA allows for extensive immune and tumor protein profiling with assessment of putative biomarkers of important for ICI treatment selection in NSCLC.

Cytology samples and molecular biomarker testing in lung cancer-advantages and challenges

This review presents an overview on molecular diagnostic in lung cancer using cytologic samples. Every patient with advanced non-small cell lung cancer (NSCLC) should be tested for targetable driver mutations and gene arrangements. If a mutation is found, this may open an option for targeted therapy. As most of the NSCLC patients in advanced stage of disease are no candidates for surgery, these tests have to be performed on small biopsies or cytology samples. The most common and treatable gene alterations should be tested in every patient: EGFR, ALK, ROS1. A growing number of other genetic changes with targetable mutations may become treatable in the near future. To find patients who might profit from inclusion into clinical studies, relevant additional markers may be tested in an appropriate context. Another important approach for treatment is immunotherapy of lung cancer, which is guided by status of PD-L1 expression on tumour cells. The use of cytology samples carries considerable advantages: often, DNA of high quality is extracted thus enabling easy and precise analysis, and samples may be easily obtained. In case of effusions, effusion fluid seldom is not aspirated for immediate patient relief, so no additional dedicated procedure is needed. Some challenges exist: If the tumour cell count is low, mutations with a low allelic frequency may be missed. In cellblocks formalin-induced DNA, damage may obviate any DNA analysis. In very cellular smears, FISH may be impossible due to massive overlapping of nuclei. Autofluorescence may impede FISH analysis. Although there is no real universal test for genomic profiling for lung cancer, the pathology laboratory must be prepared to offer different assays on different specimens in order to address turnaround time and optimise detections of difficult tumour alterations such as gene fusions. The data from the literature demonstrate that cytology show consistent results, and it is a good alternative for lung cancer molecular testing.