Diagnostic Utility of Bronchial Brush-Tip Washings for the Immunohistochemical Assessment of Peripheral Lung Lesions

Integrating endobronchial ultrasound bronchoscopy with molecular testing of immunotherapy biomarkers in non-small cell lung cancer

Immunotherapy has transformed treatment of advanced non-small-cell lung cancer (NSCLC) patients leading to remarkable long-term survival benefit. However, only about 20% of advanced NSCLC patients typically respond to immune checkpoint inhibitors (ICIs) that target the PD-1/PD-L1 pathway. The only validated biomarker for ICI therapy is the PD-L1 immunohistochemistry (IHC) test, which is considered an imperfect assay due to several variables including availability and integrity of tumour tissue, variability in staining/scoring techniques and heterogeneity in PD-L1 protein expression within and across tumour biopsies. Herein, we discuss integrating minimally invasive EBUS bronchoscopy procedures with novel molecular approaches to improve accuracy and sensitivity of PD-L1 testing. EBUS guided bronchoscopy facilitates repeated sampling of tumour tissue to increase the probability of detecting PD-L1 positive tumours. Since intra-tumoural PD-L1 (CD274) copy number is reported to be less heterogeneous than PD-L1 protein detection, quantifying PD-L1 transcript levels may increase detection of PD-L1 positive tumours. PD-L1 transcript levels show excellent concordance with PD-L1 IHC scoring and multiplex digital droplet PCR (ddPCR) assays that quantify absolute PD-L1 transcript copy number have been developed. ddPCR can also be automated for high throughput detection of low abundant variants with excellent sensitivity and accuracy to improve the broader application of diagnostic cut-off values. Optimizing diagnostic workflows that integrate optimal EBUS bronchoscopy procedures with emerging molecular ICI biomarker assays may improve the selection criteria for ICI therapy benefit.

Adequate tumour cellularity is essential for accurate PD-L1 immunohistochemistry assessment on cytology cell-block specimens

OBJECTIVES

PD-L1 immunohistochemistry (IHC) is an essential predictive biomarker for patients with non-small cell lung cancer (NSCLC), required to inform treatment decisions regarding anti-PD-1 immune checkpoint inhibitor therapy. This study aims to investigate the concordance between PD-L1 IHC assessed on NSCLC cytology and histology specimens and to determine the impactce of tumour cellularity.

METHODS

Matched cytology and histology NSCLC specimens were retrieved from the archives of the Royal Melbourne Hospital and the Royal Prince Alfred Hospital. PD-L1 IHC was performed concurrently on both specimens at the Peter MacCallum Cancer Centre using the SP263 assay kit on the Ventana Benchmark Ultra staining platform and scored by two experienced pathologists.

RESULTS

Overall agreement between matched cytology and histology specimens was good (intraclass correlation coefficient = 0.653, n = 58); however, markedly increased when the analysis was limited to cell-blocks with >100 tumour cells (intraclass correlation coefficient = 0.957, n = 29). Specificity at both 1% and 50% cut-offs was high regardless of cellularity; however, sensitivity decreased in samples with <100 tumour cells.

CONCLUSIONS

PD-L1 IHC on cytology cell-block specimens in NSCLC is an acceptable alternative to histological specimens, provided adequate tumour cells are present. Clinicians and pathologists should be mindful of the risk of false negative PD-L1 IHC in samples with low tumour cellularity, to avoid excluding patients from potentially beneficial treatment.

Sensitive molecular testing methods can demonstrate NSCLC driver mutations in malignant pleural effusion despite non-malignant cytology

Malignant pleural effusion (MPE) may be diagnosed by cytologic evaluation of pleural fluid, though false negative results can occur. Pleural effusions may provide a source of tumour material for genotyping in lung cancer patients. Detection of MPE may be improved through use of highly sensitive molecular techniques. We identified five patients with non-small cell lung cancer (NSCLC) with initial pleural fluid samples that were non-malignant on cytology, but were subsequently clinically confirmed to have MPE. Tumour mutation status was confirmed via routine testing of diagnostic clinical specimens. Cytologically negative pleural fluid cell-block specimens were analysed by amplicon-based parallel sequencing (APS) for somatic mutations commonly detected in NSCLC, and selected cases by improved and complete enrichment CO-amplification at lower denaturation temperature PCR (ICECOLD PCR) for known mutations. Mutations were detected in three out of three (sensitivity 100%) cytologically non-malignant pleural fluids from patients with a known mutation: two patients with known Kirsten rat sarcoma (KRAS) mutation demonstrated the same KRAS mutation in their pleural fluids by APS, both at approximately 2% mutant allele frequency. In one patient with a known KRAS mutation, ICECOLD PCR detected the same KRAS variant at 0.7% frequency. No mutations were detected in patients with wild-type findings from reference samples (specificity 100%). Sensitive DNA sequencing methods can detect cancer-driver mutations in cytologically non-malignant pleural fluid specimens from NSCLC patients with MPE. Our findings demonstrate the feasibility of sensitive molecular diagnostic techniques for improvement of diagnostic assessment of pleural effusions in patients with lung cancer.

Role of Immunocytochemistry in the Cytological Diagnosis of Pulmonary Tumors

Pulmonary cytology is a challenging diagnostic tool, and it is usually evaluated considering medical history and radiological findings in order to reach an accurate diagnosis. Since the majority of lung cancer patients have an advanced stage at diagnosis, a cytological specimen is frequently the only material available for diagnosis and further prognostic/predictive marker determination. Several types of specimens can be obtained from the respiratory system (including sputum, bronchoalveolar lavage, bronchial brushing, fine needle aspiration, and pleural fluid) with different technical preclinical management protocols and different diagnostic yields. Immunocytochemistry (ICC) has a pivotal role in the determination of diagnostic, prognostic, and predictive markers. Therefore, limited cytology samples are to be used with a cell-sparing approach, to allow both diagnostic ICC evaluation as well as predictive marker assessment by ICC or specific molecular assays. In this review, we describe the most common ICC markers used for the diagnosis and prognostic/predictive characterization of thoracic tumors in different cytological specimens.

Bronchoscopic Brushing from Central Lung Cancer-Next Generation Sequencing Results are Reliable

The role of bronchoscopic brushing for tumor detection and molecular testing in central lung cancer is unclear. In this study, 50 consecutive subjects with suspected central lung cancer underwent bronchoscopic brushing (31 males, median age 70, 5 never smokers). Histological results were: NSCLC/SCLC/low-grade-NET/granulation tissue in 36/8/2/4 cases. Next generation sequencing (NGS) was feasible in 62% of tumor-positive brush smear samples. In 78% of these cases, NGS displayed identical results compared to histology samples, in 22% NGS from brush smears detected specific mutations, whereas DNA quality from forceps biopsy was insufficient for NGS analysis. Sensitivity, specificity, positive predictive value, negative predictive value of brush smear analysis were 66% (95% confidence interval 50-79), 100% (40-100), 100% (85-100), and 21% (7-46). For the combined analysis of brush smear, brush tip washing and sheath tube content sensitivity was slightly elevated at 69% (53-81). In central lung cancer, bronchoscopic brushing detects tumor cells in about two-third of cases and allows a decision for or against targeted therapy in the majority of tumor-positive cases on the basis of NGS analysis.

Molecular analysis of small tissue samples obtained via transbronchial lung biopsy using radial probe endobronchial ultrasound

BACKGROUND

Radial probe endobronchial ultrasound using a guide sheath (EBUS-GS) is used to diagnose peripheral lung cancer. The aim was to identify the accuracy of molecular analysis that were performed with EBUS-GS specimens in patients with non-small cell lung cancer (NSCLC).

METHOD

From December 2015 to September 2017, we retrospectively studied 91 patients with peripheral NSCLC who underwent surgery after EBUS-GS. Epidermal growth factor receptor (EGFR) mutational and anaplastic lymphoma kinase (ALK) translocation status obtained from surgical specimens served as the references.

RESULTS

Compared to the reference data, EGFR mutational testing of EBUS-GS specimens was in 97% agreement, and the κ coefficient was 0.931 (P< 0.001). In addition, on ALK translocation testing, the results of all 91 patients were in agreement with the reference data (concordance rate of 100%, κ coefficient 1.000; P< 0.001).

CONCLUSION

We found that EBUS-GS could be used for molecular diagnosis, such as EGFR mutational and ALK translocation status, in patients with peripheral NSCLC.

A Novel Approach to Detect Programed Death Ligand 1 (PD-L1) Status and Multiple Tumor Mutations Using a Single Non-Small-Cell Lung Cancer (NSCLC) Bronchoscopy Specimen

Multiple biomarkers are under evaluation to guide the use of immune checkpoint inhibitors in non-small-cell lung cancer (NSCLC), including programed death ligand 1 (PD-L1) tumor cell staining. We have developed a new approach that accurately quantifies PD-L1 status and identifies multiple mutations by using a single bronchoscopy specimen. A novel molecular marker was identified to detect the presence of malignant cells in radial endobronchial ultrasound bronchial brushings from NSCLC (n = 15) and benign (n = 13) nodules by quantitative real-time RT-PCR (RT-qPCR). The MMP9:TIMP3 transcript ratio was significantly increased in NSCLC and using receiver operating characteristic curve analysis accurately discriminated malignant and benign bronchoscopy specimens (area under the curve = 0.98; 95% CI, 0.93-1; P < 0.0001). Utilizing the same specimens, PD-L1 expression and multiple oncogenic mutations were detected by RT-qPCR and next-generation sequencing. A second archive of snap-frozen squamous cell carcinoma (n = 40) and control (n = 20) biopsies with matching formalin-fixed, paraffin-embedded slides were used to compare PD-L1 status by immunohistochemistry and RT-qPCR. The biopsy cohort confirmed that the MMP-9:TIMP3 ratio was predictive of malignancy and demonstrated that PD-L1 transcript expression was concordant with PD-L1 tumor cell membrane staining in NSCLC (Spearman r = 0.636, P < 0.0001). This rapid molecular approach can detect malignant cells and using the same single bronchoscopy specimen can generate high-quality unfixed nucleic acid that accurately quantify PD-L1 status and identify multiple oncogenic mutations.

The feasibility of molecular testing on cell blocks created from brush tip washings in the assessment of peripheral lung lesions

BACKGROUND

With the rapid development of genotype-guided therapies, molecular testing is becoming important in the management of lung cancer. Bronchoscopy is one of the most common investigations performed to diagnose and investigate lung cancer. Given the limited samples often produced by bronchoscopy, this study aims to evaluate the feasibility of performing molecular testing on cell blocks created from bronchoscope cytology brush tip washings (BTW).

METHODS

Patients with positive brush cytology for tumour cells had cell blocks created from the BTW. Mutations were detected using amplicon-based massively parallel sequencing of targeted regions of EGFR, KRAS, and BRAF genes.

RESULTS

A total of 45 patients were included in this study. Of those, 91% had adequate specimens for molecular analysis and 66% of patients with adenocarcinoma had mutations detected. Bronchial brush tip wash cell blocks were the sole specimen available for molecular testing in 27 (60%) patients.

CONCLUSIONS

The findings of this study demonstrate that molecular testing can be performed on cell blocks created from BTW and this technique may allow for an increase in bronchoscope specimens amenable to molecular testing without further increasing morbidity and mortality.