Formalin fixation for optimal concordance of programmed death-ligand 1 immunostaining between cytologic and histologic specimens from patients with non-small cell lung cancer

Why PD-L1 expression varies between studies of lung cancer: results from a Bayesian meta-analysis

PD-L1 expression is an important biomarker for the management of non-small cell lung cancer (NSCLC) but has been highly heterogeneous across studies. We developed a statistical model to reconcile conflicting estimates of PD-L1 prevalence by accounting for between-study variation in test sensitivity, specimen age, and laboratory count. In doing so, we obtained refined estimates for PD-L1 expression prevalence and identified differences by histological subtype, mutational status, and stage. Across 92 studies published between 2015 and 2023, the detectability of PD-L1 declined with increasing specimen age while the consistency of detection rates was greater for studies incorporating data from a higher number of laboratories. Using the 22C3 antibody as a benchmark, we predicted that 58.3% (95% CrI 49.8-66.1%) and 27.0% (95% CrI 21.2-33.1%) of NSCLC will have PD-L1 tumour proportion scores at the ≥ 1% and ≥ 50% threshold. PD-L1 expression was lower in EGFR-mutated NSCLC and higher in NSCLC with ALK, KRAS, MET, ROS1, and RET alterations. PD-L1 expression was more common with later-stage disease. Overall, this work highlights the continuing challenge of consistency in PD-L1 testing. Although the underlying prevalence of PD-L1 expression varies in the lung cancer population based on tumour-related factors, controllable differences in testing parameters also account for variations in PD-L1 prevalence.

Development of a Novel Peptide with RGD Tumor Homing Motif: Evaluation of its Anticancer Potential in Hepatocellular Carcinoma and Colon Cancer Cells

BACKGROUND

Peptide-based therapy has emerged as a promising avenue for treating various disorders, and recent research has highlighted the potential of anti-cancer peptides (ACPs) in cancer treatment. In this context, this study aimed to design a novel peptide incorporating a tumor-homing peptide (RGD) and C-amidation to enhance its anticancer activity, particularly against liver (HepG2) and colon (HCT-116) cancer cell lines.

OBJECTIVES

The primary objective was to design a peptide with improved anticancer properties by leveraging the tumor-homing capabilities of RGD and enhancing its activity through C-amidation. The study sought to evaluate the cytotoxicity of the designed peptide against red blood cells (RBCs) and normal Vero cells. Furthermore, the anticancer efficacy of the peptide was assessed in hepatocellular carcinoma (HepG2) and colon cancer (HCT-116) cell lines. The specific objectives included examining the apoptotic induction and morphological changes in treated cells compared to untreated cells.

METHODS

The peptide was designed using the ACPred-FL bioinformatics tool, and its cytotoxicity was assessed through hemolysis assays against RBCs and normal Vero cells. Anticancer activity was evaluated against HepG2 and HCT-116 cell lines. The analysis of apoptotic induction involved measuring the relative gene expression of oncogenic marker BCL2 and apoptotic markers (BAX, BID, CAS-8). Additionally, Cytopathological examination and Western Blot analysis were employed to study morphological changes and confirm the quantification of relevant markers.

RESULTS

The designed peptide, consisting of twelve amino acids with a molecular mass of 1230.6233 Da and an isoelectric point of 9.81, exhibited low erythrocyte lysis and minimal toxicity to normal cells. The IC50 values demonstrated significant anticancer activity against both HepG2 (36.49±2.6 μg/mL) and HCT-116 (11.03±2.5 μg/mL) cell lines. Treated cells exhibited a significant decrease in the oncogenic marker BCL2 and an upregulation of apoptotic markers (BAX, BID, CAS-8). Western Blot analysis confirmed these results in addition to cytopathological examination that scattered apoptotic and degenerative changes.

CONCLUSION

The designed peptide is considered a patent product that displayed remarkable anticancer activity against hepatocellular carcinoma and colon cancer cell lines, effectively modulating apoptotic and oncogenic markers. These findings highlight the potential of the peptide as a therapeutic agent for cancer treatment, emphasizing its clinical significance in combating liver and colon cancers. Nonetheless, further research and development are warranted to explore the translational potential of this peptide in clinical studies.

Comparison of Claudin-4, BerEP4, Carcinoembryonic Antigen and MOC31 in Serous Fluids Metastases Demonstrate High Sensitivity of Claudin-4 at Low Cellularity

INTRODUCTION

Claudin-4 has been described as a highly sensitive immunocytochemical marker for detection of metastatic carcinoma cells in effusion cytology specimens. This study aims to challenge the performance of claudin-4 in different types of malignancies and low cellularity specimens, by comparison with other markers in a large cohort of carcinomatous effusion specimens.

METHODOLOGY

Cell block preparations from peritoneal and pleural fluid specimens were retrieved, with malignant (carcinoma) diagnoses confirmed by review of hospital diagnosis code and pathology reports. Claudin-4, BerEP4, CEA, and MOC31 immunocytochemistry were performed and scored by expression proportion and intensity. Tumor cellularity was assessed for subgroup analysis of low cellularity specimens.

RESULTS

Totally 147 specimens (70 pleural, 77 peritoneal) of 68 lung, 62 breast, 9 gynecological, and 7 gastrointestinal carcinomas were retrieved. The average proportion expression of claudin-4 was highest (89.6%, vs. CEA 40.5%, BerEp4 18.6%, MOC31 16.8%) and the percentage of strong expression was highest for claudin-4 (72.1%). Expression levels of claudin-4 were consistently higher than other markers in subgroups of all primary sites. The difference was more significant for low cellularity specimens. High (≥50%) proportion expression was seen for 96.61% of cases for claudin-4 (vs. BerEp4 8.77%, CEA 46.55%, MOC31 8.77%, p < 0.001). These factors contributed to a low concordance between claudin-4 and BerEp4, CEA and MOC31 (K = 0.010-0.043).

CONCLUSION

Claudin-4 is more sensitive than CEA, BerEp4 and MOC31, suitable for low cellularity specimens of most types of metastatic carcinoma and is a robust immunocytochemical marker for carcinoma that can be used solitarily.

Diagnostic and Predictive Immunocytochemistry in Lung Cancer

BACKGROUND

Immunocytochemistry (ICC) is suitable for use on a range of cytology preparations, such as cell blocks, air-dried slides, ethanol-fixed slides, direct smears, cytospins, and liquid-based cytology (LBC) samples. However, it must be standardized against the gold standard of formalin-fixed paraffin-embedded tissues with adequate number of positive and negative controls. The role of ICC in lung cancer is crucial, as most lung cancer specimens are cytology samples. Accurate diagnosis and testing of certain biomarkers rely heavily on both diagnostic and predictive ICC.

SUMMARY

Key ICC markers important in lung cancer include, but are not limited to, diagnostic ICCs such as TTF-1, p40, Napsin A, and p63, as well as predictive ICCs like ALK, ROS-1, PD-L1, and NTRK.

KEY MESSAGES

With proper validation, immunocytochemistry for lung cancer can be effectively performed on direct smears, cytospins, and other specimens, even when resources for preparing cell blocks are unavailable. This is particularly true for diagnostic antibodies, but it is important to exercise caution with predictive ICC. Nonetheless, a low threshold for molecular testing should be maintained. PD-L1 ICC can be challenging and should ideally be performed on formalin-fixed cell blocks or biopsies when available.

BACKGROUND

Immunocytochemistry (ICC) is suitable for use on a range of cytology preparations, such as cell blocks, air-dried slides, ethanol-fixed slides, direct smears, cytospins, and liquid-based cytology (LBC) samples. However, it must be standardized against the gold standard of formalin-fixed paraffin-embedded tissues with adequate number of positive and negative controls. The role of ICC in lung cancer is crucial, as most lung cancer specimens are cytology samples. Accurate diagnosis and testing of certain biomarkers rely heavily on both diagnostic and predictive ICC.

SUMMARY

Key ICC markers important in lung cancer include, but are not limited to, diagnostic ICCs such as TTF-1, p40, Napsin A, and p63, as well as predictive ICCs like ALK, ROS-1, PD-L1, and NTRK.

KEY MESSAGES

With proper validation, immunocytochemistry for lung cancer can be effectively performed on direct smears, cytospins, and other specimens, even when resources for preparing cell blocks are unavailable. This is particularly true for diagnostic antibodies, but it is important to exercise caution with predictive ICC. Nonetheless, a low threshold for molecular testing should be maintained. PD-L1 ICC can be challenging and should ideally be performed on formalin-fixed cell blocks or biopsies when available.

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.

The updated College of American Pathologists principles of analytic validation of immunohistochemical assays: A step forward for cytopathology

Updated College of American Pathologists guideline recommendations include specific guidelines for validating immunohistochemistry assays performed on cytology specimens. The new recommendations may be the impetus needed to open the door to a wider adoption of cytology specimens into routine clinical practice for immunochemistry‐based assays that drive patient care and biomarker‐driven therapeutics.

Multi-Tissue Controls and Multiplex Immunocytochemistry in Pulmonary Cytology

INTRODUCTION

The World Health Organization 2021 lung cancer classification highlights the central role of immunohistochemistry (IHC) in diagnostic pathology. Despite traditional IHC being essential, its limitation to one marker per tissue section brings challenges, particularly when facing cytological limitedly sized samples. To overcome these challenges, multiplex immunocytochemistry (mICC) techniques offer the simultaneous detection of multiple markers from a single section. These advances complement the highly complex imaging techniques that enable additional analyses of cellular interactions.

METHODS

The present study outlines a comprehensive mICC methodology of an automated multiplex immunoperoxidase staining method and multiple tissue hybrid controls for ICC/mICC. Protocols are presented in detail and demonstrate a careful approach to optimizing various markers for diagnostic workup including immunotherapy.

CONCLUSION

Multiplex IHC/ICC emerges as a transformative force in biomedical diagnostics and research. Beyond simultaneous marker detection, it unravels complexities within tissues - unveiling co-localization nuances, deciphering expression patterns, and enhancing understanding of cellular populations. As personalized treatments gain prominence, the study emphasizes the heightened importance of diagnostic tools and sample adequacy. The present methodological study, encapsulating an automated multiplex immunoperoxidase staining method, symbolizes a stride towards precision in pulmonary carcinoma diagnosis. Multi-tissue controls represent a key element in quality assurance in pathology laboratories.

Principles of Analytic Validation of Immunohistochemical Assays: Guideline Update

CONTEXT.—

In 2014, the College of American Pathologists developed an evidence-based guideline to address analytic validation of immunohistochemical assays. Fourteen recommendations were offered. Per the National Academy of Medicine standards for developing trustworthy guidelines, guidelines should be updated when new evidence suggests modifications.

OBJECTIVE.—

To assess evidence published since the release of the original guideline and develop updated evidence-based recommendations.

DESIGN.—

The College of American Pathologists convened an expert panel to perform a systematic review of the literature and update the original guideline recommendations using the Grading of Recommendations Assessment, Development and Evaluation approach.

RESULTS.—

Two strong recommendations, 1 conditional recommendation, and 12 good practice statements are offered in this updated guideline. They address analytic validation or verification of predictive and nonpredictive assays, and recommended revalidation procedures following changes in assay conditions.

CONCLUSIONS.—

While many of the original guideline statements remain similar, new recommendations address analytic validation of assays with distinct scoring systems, such as programmed death receptor-1 and analytic verification of US Food and Drug Administration approved/cleared assays; more specific guidance is offered for validating immunohistochemistry performed on cytology specimens.

The detection of PD-L1 expression on liquid-based cytology in pleural effusion of lung adenocarcinoma and its prognostic evaluation: Between paired liquid-based cytology and cell block samples

BACKGROUND

Programmed death-ligand 1 (PD-L1) expression levels measured by immunohistochemistry have been proven to predict the outcome of immunotherapy in lung adenocarcinoma (LUAD). However, data on PD-L1 expression on liquid-based cytology (LBC) in malignant pleural effusion (MPE) is scarce.

METHODS

This study cohort included 60 cases with MPE suffering from LUAD. PD-L1 SP263 assay was used for immunocytochemistry (ICC) on LBC and matched cell block (CB) to validate ICC protocols on LBC slides. Clinical outcomes were analyzed based on immunotherapy and PD-L1 tumor proportion scores (TPS) on LBC slides and CBs.

RESULTS

PD-L1 expression with TPS ≥1% was lower in LBCs than in CBs (33 of 60 [55.0%] vs. 35 of 60 [58.3%]; p = .687). Even with the TPS ≥50% threshold, PD-L1 expression was lower in LBCs (10 of 60 [16.7%] vs. 15 of 60 [25%]; p = .125). Epidermal growth factor receptor (EGFR) exon 20 mutation, tumor cell proportion, and pleural fluid neutrophil-to-lymphocyte ratio were related to PD-L1 expression on CBs (p = .013, p = 0.022, and p = .011), respectively. Patients with subsequent immune checkpoint inhibitor therapy remained a better prognostic in subgroups of PD-L1 positive expression on LBC slides (TPS ≥1%, p = .041).

CONCLUSIONS

LBC specimens had comparable performance to CBs in PD-L1 assessment and predicting treatment response to PD-L1-defined therapy.

Evaluation of a Novel Fixative Solution for Liquid-Based Cytology in Diagnostic Cytopathology

Since its introduction in the early 2000s, liquid-based cytology (LBC) has been increasingly used for gynecologic and non-gynecologic cytology, and its multiple advantages have been widely recognized. The aim of this study was to investigate the use of a new fixative and pre-analytical method for morphological diagnosis in cytological samples. In particular, we evaluated the effect of a novel preservative solution on the preparation of diagnostic slides by comparing it with the standard reference used globally in cytology laboratories. This study included both gynecological (n = 139) and non-gynecological (n = 183) samples. Several morphologic variables were then identified and evaluated. Using this approach, we were then able to demonstrate the suitability of the new system, with improved safety, to be integrated within current pathology clinical practice. Overall, using a safer preservative solution, the study shows no statistical difference (and then non-inferiority) in the new fixation protocol compared with the standard reference used in routine practice in terms of diagnostic adequacy, evaluated both in clinically relevant gyn and non-gyn datasets.

Assessing PD-L1 Expression in Head and Neck Squamous Cell Carcinoma: Trials and Tribulations

Immune checkpoint inhibitors have improved the outcome of patients diagnosed with inoperable recurrent or metastatic head and neck squamous cell carcinoma. However, as only a subset of head and neck cancer patients benefit from this treatment, biomarkers predicting treatment response help guide physicians in their clinical decision-making. PD-L1 expression assessed by immunohistochemistry is the single most clinically relevant biomarker predicting response to PD-1-blocking antibodies. Here, we discuss in which clinical context assessment of PD-L1 expression is instrumental for the choice of therapy, how pathologists score it, and how it affects the approval of anti-PD-1 antibodies. Furthermore, we discuss the heterogeneity of PD-L1 expression and review technical aspects of determining this prominent biomarker-knowledge that might influence clinical decision-making.

Impact of Decalcification, Cold Ischemia, and Deglycosylation on Performance of Programmed Cell Death Ligand-1 Antibodies With Different Binding Epitopes: Comparison of 7 Clones

Programmed cell death ligand-1 (PD-L1) expression levels in patients' tumors have demonstrated clinical utility across many cancer types and are used to determine treatment eligibility. Several independently developed PD-L1 immunohistochemical (IHC) predictive assays are commercially available and have demonstrated different levels of staining between assays, generating interest in understanding the similarities and differences between assays. Previously, we identified epitopes in the internal and external domains of PD-L1, bound by antibodies in routine clinical use (SP263, SP142, 22C3, and 28-8). Variance in performance of assays utilizing these antibodies, observed following exposure to preanalytical factors such as decalcification, cold ischemia, and duration of fixation, encouraged additional investigation of antibody-binding sites, to understand whether binding site structures/conformations contribute to differential PD-L1 IHC assay staining. We proceeded to further investigate the epitopes on PD-L1 bound by these antibodies, alongside the major clones utilized in laboratory-developed tests (E1L3N, QR1, and 73-10). Characterization of QR1 and 73-10 clones demonstrated that both bind the PD-L1 C-terminal internal domain, similar to SP263/SP142. Our results also demonstrate that under suboptimal decalcification or fixation conditions, the performance of internal domain antibodies is less detrimentally affected than that of external domain antibodies 22C3/28-8. Furthermore, we show that the binding sites of external domain antibodies are susceptible to deglycosylation and conformational structural changes, which directly result in IHC staining reduction or loss. The binding sites of internal domain antibodies were unaffected by deglycosylation or conformational structural change. This study demonstrates that the location and conformation of binding sites, recognized by antibodies employed in PD-L1 diagnostic assays, differ significantly and exhibit differing degrees of robustness. These findings should reinforce the need for vigilance when performing clinical testing with different PD-L1 IHC assays, particularly in the control of cold ischemia and the selection of fixation and decalcification conditions.

Effect of liquid-based cytology fixing solution on immunocytochemistry: Efficacy of antigen retrieval in cytologic specimens

BACKGROUND

Immunocytochemistry (ICC) is an indispensable technique to improve diagnostic accuracy. ICC using liquid-based cytology (LBC)-fixed specimens has been reported. However, problems may arise if the samples are not fixed appropriately. We investigated the relationship between the LBC fixing solution and ICC and the usefulness of antigen retrieval (AR) in LBC specimens.

METHODS

Specimens were prepared from five types of LBC-fixed samples using cell lines and the SurePath™ method. ICC was performed using 13 antibodies and analyzed by counting the number of positive cells in the immunocytochemically stained specimens.

RESULTS

Insufficient reactivity was observed using ICC without heat-induced AR (HIAR) in nuclear antigens. The number of positive cells increased in ICC with HIAR. The percentage of positive cells was lower in CytoRich™ Blue samples for Ki-67 and in CytoRich™ Red and TACAS™ Ruby samples for estrogen receptor and p63 than in the other samples. For cytoplasmic antigens, the percentage of positive cells for no-HIAR treatment specimens was low in the three antibodies used. In cytokeratin 5/6, the number of positive cells increased in all LBC specimens with HIAR, and the percentage of positive cells in CytoRich™ Red and TACAS™ Ruby samples was significantly lower (p < .01). For cell membrane antigens, CytoRich™ Blue samples had a lower percentage of positive cells than the other LBC-fixed samples.

CONCLUSION

The combination of detected antigen, used cells, and fixing solution may have different effects on immunoreactivity. ICC using LBC specimens is a useful technique, but the staining conditions should be examined before performing ICC.

Cutoff values of PD-L1 expression in urinary cytology samples for predicting response to immune checkpoint inhibitor therapy in upper urinary tract urothelial carcinoma

BACKGROUND

The objective of this study was to determine the cutoff value of PD-L1 expression that can predict response to immune checkpoint inhibitor (ICI) immunotherapy for upper tract urothelial carcinoma (UTUC).

METHODS

The concordance of PD-L1 expression between paired surgical resection specimens (SRSs) and urine cell blocks (UCBs) (cohort 1) was studied in a retrospective set of 58 UTUC patients to determine its suitability as a predictor of ICI immunotherapy efficacy. PD-L1 expression in UCBs obtained before neoadjuvant ICI immunotherapy was verified in a prospective set of 12 UTUC patients (cohort 2). PD-L1 (SP263 clone) expression was assessed for percentage (tumor proportional score) of tumor cell (TC) showing PD-L1 staining.

RESULTS

The authors found an overall agreement of 94.4% (51 of 54) between UCBs and SRSs in cohort 1 (positive percent agreement = 100%, negative percent agreement = 93.8%, r value = 0.63). PD-L1 expression in <10% and ≥10% of tumor cells (TCs) of UCBs were the best predictors of negative (<25%) and positive (≥25%) expression in TCs of SRSs, respectively (concordance = 98.1%, r value = 0.93). These findings were verified in cohort 2: at the 10% cutoff for PD-L1 expression, the best response predictive value was 83.3% (5 of 6) in PD-L1-positive patients, and the nonresponse predictive value was 50% (3 of 6) in PD-L1-negative patients. The sensitivity, specificity, and area under the receiver operating characteristic curve values for predicting ICI immunotherapy efficacy based on PD-L1-expressing TCs in UCBs were 62.5%, 75%, and 0.688, respectively.

CONCLUSIONS

Immunocytochemistry of UCBs is reliable for determining PD-L1 expression, which can predict the efficacy of ICI immunotherapy at a cutoff of 10%.

PD-L1 immunohistochemical testing: A review with reference to cytology specimens

BACKGROUND

Immunotherapy based on disruption of the PD-1/PD-L1 axis is standard of care for many high stage malignancies including melanomas, non-small cell carcinomas of the lung, triple negative breast carcinomas, and squamous cell carcinomas of the head and neck. Eligibility for immunotherapy requires immunohistochemical assessment of PD-L1 expression. Currently, many high stage malignancies are diagnosed by cytology and cytologic material is the only specimen available for ancillary testing. Formal guidelines do not currently exist defining the optimal specimen type, antibody to be used or the best scoring system for cytologic material. Significant information has been published for PD-L1 testing of pulmonary specimens but much less data exists for the reproducibility, accuracy and best practices for material obtained from other body sites and types of malignancy.

METHODS

We searched the PubMed data base for manuscripts relating to PD-L1 testing of cytologic specimens. The search period was between 2016 and 2022. The search terms used were PD-L1, cytology, FNA, immunotherapy, immunohistochemistry, immunocytochemistry, cytology-histology correlation. Cross referencing techniques were used to screen for the most relevant manuscripts. The abstracts of these were then reviewed for final data collection and analysis.

RESULTS

A total of 86 studies were identified conforming to study relevancy. These were reviewed in their entirety by two authors (LJL, TZ) for extraction of data. The majority of studies involved pulmonary specimens (79) with three relating to PD-L1 testing of head and neck cytologic specimens and one each for PD-L1 testing of cytology specimens from melanomas, pancreas, pleural fluids, and triple negative breast carcinomas. While smears could be used, most studies found cell blocks optimal for testing.

SUMMARY

Currently, four drugs are approved for immunotherapy based on PD-L1 status. These drugs require specific antibody clones as well as scoring systems. Scoring systems and cut points vary with the type of neoplasm being treated. Cytology specimens from the lung, head and neck and melanomas can all be used for PD-L1 testing with good agreement with corresponding histology specimens.

Nationwide differences in cytology fixation and processing methods and their impact on interlaboratory variation in PD-L1 positivity

Programmed death ligand-1 (PD-L1) immunostaining, which aids clinicians in decision-making on immunotherapy for non-small cell lung cancer (NSCLC) patients, is sometimes performed on cytological specimens. In this study, differences in cytology fixation and cell block (CB) processing between pathology laboratories were assessed, and the influence of these differences on interlaboratory variation in PD-L1 positivity was investigated. Questionnaires on cytology processing were sent to all Dutch laboratories. Information gathered from the responses was added to data on all Dutch NSCLC patients with a mention of PD-L1 testing in their cytopathology report from July 2017 to December 2018, retrieved from PALGA (the nationwide network and registry of histo- and cytopathology in the Netherlands). Case mix-adjusted PD-L1 positivity rates were determined for laboratories with known fixation and CB method. The influence of differences in cytology processing on interlaboratory variation in PD-L1 positivity was assessed by comparing positivity rates adjusted for differences in the variables fixative and CB method with positivity rates not adjusted for differences in these variables. Twenty-eight laboratories responded to the survey and reported 19 different combinations of fixation and CB method. Interlaboratory variation in PD-L1 positivity was assessed in 19 laboratories. Correcting for differences in the fixative and CB method resulted in a reduction (from eight (42.1%) to five (26.3%)) in the number of laboratories that differed significantly from the mean in PD-L1 positivity. Substantial variation in cytology fixation and CB processing methods was observed between Dutch pathology laboratories, which partially explains the existing considerable interlaboratory variation in PD-L1 positivity.

Program death ligand-1 immunocytochemistry in lung cancer cytological samples: A systematic review

In this era of personalized medicine, targeted immunotherapies like immune checkpoint inhibitors (ICI) blocking the programmed death-1 (PD-1)/program death ligand-1 (PD-L1) axis have become an integral part of treating advanced stage non-small cell lung carcinoma (NSCLC) and many other cancer types. Multiple monoclonal antibodies are available commercially to detect PD-L1 expression in tumor cells by immunohistochemistry (IHC). As most clinical trials initially required tumor biopsy for PD-L1 detection by IHC, many of the currently available PD-1/PD-L1 assays have been developed and validated on formalin fixed tissue specimens. The majority (>50%) of lung cancer cases do not have a surgical biopsy or resection specimen available for ancillary testing and instead must rely primarily on fine needle aspiration biopsy specimens for diagnosis, staging and ancillary tests. Review of the literature shows multiple studies exploring the feasibility of PD-L1 IHC on cytological samples. In addition, there are studies addressing various aspects of IHC validation on cytology preparations including pre-analytical (e.g., different fixatives), analytical (e.g., antibody clone, staining platforms, inter and intra-observer agreement, cytology-histology concordance) and post-analytical (e.g., clinical outcome) issues. Although promising results in this field have emerged utilizing cytology samples, many important questions still need to be addressed. This review summarizes the literature of PD-L1 IHC in lung cytology specimens and provides practical tips for optimizing analysis.

PD-L1 Expression in Non-Small Cell Lung Cancer: Data from a Referral Center in Spain

Anti-programmed cell death (PD1)/ligand-1 (PD-L1) checkpoint inhibitors have improved the survival of non-small cell lung cancer (NSCLC) patients. Additionally, PD-L1 has emerged as a predictive biomarker of response. Our goal was to examine the histological features of all PD-L1 cases of NSCLC analyzed in our center between 2017 and 2020, as well as to correlate the expression values of the same patient in different tested samples. PD-L1 immunohistochemistry (IHC) was carried out on 1279 external and internal samples: 482 negative (tumor proportion score, TPS < 1%; 37.7%), 444 low-expression (TPS 1–49%; 34.7%) and 353 high-expression (TPS ≥ 50%; 27.6%). Similar results were observed with samples from our institution (N = 816). Significant differences were observed with respect to tumor histological type (p = 0.004); squamous carcinoma was positive in a higher proportion of cases than other histological types. There were also differences between PD-L1 expression and the type of sample analyzed (surgical, biopsy, cytology; p < 0.001), with a higher frequency of negative cytology. In addition, there were cases with more than one PD-L1 determination, showing heterogeneity. Our results show strong correlation with the literature data and reveal heterogeneity between tumors and samples from the same patient, which could affect eligibility for treatment with immunotherapy.

Formalin fixation for optimal concordance of programmed death-ligand 1 immunostaining between cytologic and histologic specimens from patients with non-small cell lung cancer

BACKGROUND

Immunohistochemical staining of programmed death-ligand 1 (PD-L1) is used to determine which patients with non-small cell lung cancer (NSCLC) may benefit most from immunotherapy. Therapeutic management of many patients with NSCLC is based on cytology instead of histology. In this study, concordance of PD-L1 immunostaining between cytology cell blocks and their histologic counterparts was analyzed. Furthermore, the effect of various fixatives and fixation times on PD-L1 immunoreactivity was studied.

METHODS

Paired histologic and cytologic samples from 67 patients with NSCLC were collected by performing fine-needle aspiration on pneumonectomy/lobectomy specimens. Formalin-fixed, agar-based or CytoLyt/PreservCyt-fixed Cellient cell blocks were prepared. Sections from cell blocks and tissue blocks were stained with SP263 (standardized assay) and 22C3 (laboratory-developed test) antibodies. PD-L1 scores were compared between histology and cytology. In addition, immunostaining was compared between PD-L1-expressing human cell lines fixed in various fixatives at increasing increments in fixation duration.

RESULTS

Agar cell blocks and tissue blocks showed substantial agreement (κ = 0.70 and κ = 0.67, respectively), whereas fair-to-moderate agreement was found between Cellient cell blocks and histology (κ = 0.28 and κ = 0.49, respectively). Cell lines fixed in various alcohol-based fixatives showed less PD-L1 immunoreactivity compared with those fixed in formalin. In contrast to SP263, additional formalin fixation after alcohol fixation resulted in preserved staining intensity using the 22C3 laboratory-developed test and the 22C3 pharmDx assay.

CONCLUSIONS

Performing PD-L1 staining on cytologic specimens fixed in alcohol-based fixatives could result in false-negative immunostaining results, whereas fixation in formalin leads to higher and more histology-concordant PD-L1 immunostaining. The deleterious effect of alcohol fixation could be reversed to some degree by postfixation in formalin.