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Primary pericardial mesothelioma (PPM) has no accepted standard-of-care treatment options with management and outcomes often extrapolated from diffuse pleural mesothelioma. Disease-specific research is needed to better define PPM. We report our institutional experience with PPM highlighting the potential role for multimodality therapy.Patients with PPM diagnosed by a multidisciplinary team of medical oncologists, thoracic surgeons, thoracic pathologists, and radiologists between January 2011 and January 2022 were followed to February 2022. Clinicopathologic features and treatment outcomes were annotated. Overall survival (OS) was defined from the date of pathologic diagnosis.The median age at diagnosis of the 12 patients identified with having PPM was 51 (range: 21-71) years old. Most patients were of female sex (n = 8; 67%), 75% of the samples were epithelioid (n = 9), and 25% were nonepithelioid (two sarcomatoid and one biphasic). Most cases (92%, 11 of 12) had expression of at least two mesothelial markers on immunohistochemistry. The median OS of the cohort was 25.9 months. Five patients had an OS greater than 12 months; four of whom received pericardial radiation. Three of the patients who received radiation did so as part of a trimodality approach (surgical resection, adjuvant chemotherapy, and radiation); the OS for patients who received trimodality therapy was 70.3 months versus 8.2 months for those who did not.PPM represents a distinct disease with no universally accepted treatment options. Our findings suggest that trimodality therapy may improve outcomes in selected patients with PPM.

Immunotherapy is used to treat almost all patients with advanced non-small cell lung cancer (NSCLC); however, identifying robust predictive biomarkers remains challenging. Here we show the predictive capacity of integrating medical imaging, histopathologic and genomic features to predict immunotherapy response using a cohort of 247 patients with advanced NSCLC with multimodal baseline data obtained during diagnostic clinical workup, including computed tomography scan images, digitized programmed death ligand-1 immunohistochemistry slides and known outcomes to immunotherapy. Using domain expert annotations, we developed a computational workflow to extract patient-level features and used a machine-learning approach to integrate multimodal features into a risk prediction model. Our multimodal model (area under the curve (AUC) = 0.80, 95% confidence interval (CI) 0.74–0.86) outperformed unimodal measures, including tumor mutational burden (AUC = 0.61, 95% CI 0.52–0.70) and programmed death ligand-1 immunohistochemistry score (AUC = 0.73, 95% CI 0.65–0.81). Our study therefore provides a quantitative rationale for using multimodal features to improve prediction of immunotherapy response in patients with NSCLC using expert-guided machine learning.

Purpose: Clinical patterns and the associated optimal management of acquired resistance to PD-(L)1 blockade are poorly understood. Experimental Design: All cases of metastatic lung cancer treated with PD-(L)1 blockade at Memorial Sloan Kettering were reviewed. In acquired resistance (complete/partial response per RECIST, followed by progression), clinical patterns were distinguished as oligo (OligoAR ≤ 3 lesions of disease progression) or systemic (sAR). We analyzed the relationships between patient characteristics, burden/location of disease, outcomes, and efficacy of therapeutic interventions. Results: Of 1,536 patients, 312 (20%) had an initial response and 143 developed AR (9% overall, 46% of responders). OligoAR was the most common pattern (80/143, 56%). Baseline tumor mutational burden, depth of response, and duration of response were significantly increased in oligoAR compared with sAR (P < 0.001, P = 0.03, P = 0.04, respectively), whereas baseline PD-L1 and tumor burden were similar. Post-progression, oligoAR was associated with improved overall survival (median 28 months vs. 10 months, P < 0.001) compared with sAR. Within oligoAR, post-progression survival was greater among patients treated with locally-directed therapy (e.g., radiation, surgery; HR, 0.41; P = 0.039). Fifty-eight percent of patients with oligoAR treated with locally-directed therapy alone are progression-free at last follow-up (median 16 months), including 13 patients who are progression-free more than 2 years after local therapy. Conclusions: OligoAR is a common and distinct pattern of acquired resistance to PD-(L)1 blockade compared with sAR. OligoAR is associated with improved post-progression survival and some cases can be effectively managed with local therapies with durable benefit.

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Malignant pleural diseases, comprising metastatic lung and breast cancers and malignant pleural mesothelioma (MPM), are aggressive solid tumors with poor therapeutic response. We developed and conducted a first-in-human, phase I study of regionally delivered, autologous, mesothelin-targeted chimeric antigen receptor (CAR) T-cell therapy. Intrapleural administration of 0.3M to 60M CAR T cells/kg in 27 patients (25 with MPM) was safe and well tolerated. CAR T cells were detected in peripheral blood for >100 days in 39% of patients. Following our demonstration that PD-1 blockade enhances CAR T-cell function in mice, 18 patients with MPM also received pembrolizumab safely. Among those patients, median overall survival from CAR T-cell infusion was 23.9 months (1-year overall survival, 83%). Stable disease was sustained for ≥6 months in 8 patients; 2 exhibited complete metabolic response on PET scan. Combination immunotherapy with CAR T cells and PD-1 blockade agents should be further evaluated in patients with solid tumors.Significance:Regional delivery of mesothelin-targeted CAR T-cell therapy followed by pembrolizumab administration is feasible, safe, and demonstrates evidence of antitumor efficacy in patients with malignant pleural diseases. Our data support the investigation of combination immunotherapy with CAR T cells and PD-1 blockade agents in solid tumors.See related commentary by Aldea et al., p. 2674.This article is highlighted in the In This Issue feature, p. 2659

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Despite the initial successes of immunotherapy, there is an urgent clinical need for molecular assays that identify patients more likely to respond. Here, we report that ultrasensitive measures of circulating tumor DNA (ctDNA) and T-cell expansion can be used to assess responses to immune checkpoint blockade in metastatic lung cancer patients (N = 24). Patients with clinical response to therapy had a complete reduction in ctDNA levels after initiation of therapy, whereas nonresponders had no significant changes or an increase in ctDNA levels. Patients with initial response followed by acquired resistance to therapy had an initial drop followed by recrudescence in ctDNA levels. Patients without a molecular response had shorter progression-free and overall survival compared with molecular responders [5.2 vs. 14.5 and 8.4 vs. 18.7 months; HR 5.36; 95% confidence interval (CI), 1.57–18.35; P = 0.007 and HR 6.91; 95% CI, 1.37–34.97; P = 0.02, respectively], which was detected on average 8.7 weeks earlier and was more predictive of clinical benefit than CT imaging. Expansion of T cells, measured through increases of T-cell receptor productive frequencies, mirrored ctDNA reduction in response to therapy. We validated this approach in an independent cohort of patients with early-stage non–small cell lung cancer (N = 14), where the therapeutic effect was measured by pathologic assessment of residual tumor after anti-PD1 therapy. Consistent with our initial findings, early ctDNA dynamics predicted pathologic response to immune checkpoint blockade. These analyses provide an approach for rapid determination of therapeutic outcomes for patients treated with immune checkpoint inhibitors and have important implications for the development of personalized immune targeted strategies.Significance: Rapid and sensitive detection of circulating tumor DNA dynamic changes and T-cell expansion can be used to guide immune targeted therapy for patients with lung cancer.See related commentary by Zou and Meyerson, p. 1038

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Supplementary Figures related to Figures 1, 2, 3, and 4.

Table S2: Surveillance plasma sample ctDNA metrics. Table S3: Baseline plasma sample ctDNA metrics. Table S4: Surveillance plasma sample variants in ctDNA detected samples. Table S5: Baseline plasma variants in available samples. Table S6: Tumor variants detected by whole exome and targeted sequencing. Table S7: Canonical genes implicated in clonal hematopoiesis.

Supplemental Methods

Table S1 shows summary patient demographics, pathologic features, and treatment details

Supplemental Figure 2

Supplementary Table S1. Summary of patient characteristics Supplementary Table S2. Summary of plasma samples analyzed Supplementary Table S3. Summary of peripheral blood lymphocytes and tumor infiltrating lymphocytes samples analyzed Supplementary Table S4. Genes analyzed by TEC-Seq Supplementary Table S5. Summary of TEC-Seq Characteristics Supplementary Table S6. Somatic sequence alterations detected in cfDNA Supplementary Table S7. Mutation Cellularity Analysis for tumor-specific cfDNA variants Supplementary Table S8. TCR-beta sequencing analysis Supplementary Table S9. Differentially abundant clones for CGLU111 Supplementary Table S10. Differentially abundant clones for CGLU117 Supplementary Table S11. Differentially abundant clones for CGLU127 Supplementary Table S12. Differentially abundant clones for CGLU212 Supplementary Table S13. Differentially abundant clones for CGLU135 Supplementary Table S14. Differentially abundant clones for CGLU161 Supplementary Table S15. Differentially abundant clones for CGLU159 Supplementary Table S16. Differentially abundant clones for CGLU162 Supplementary Table S17. Differentially abundant clones for CGLU203 Supplementary Table S18. Differentially abundant clones for CGLU243

Overall survival by combination of STK11, KEAP1, and SMARCA4 alteration status.

Purpose:SMARCA4 mutations are among the most common recurrent alterations in non–small cell lung cancer (NSCLC), but the relationship to other genomic abnormalities and clinical impact has not been established.Experimental Design:To characterize SMARCA4 alterations in NSCLC, we analyzed the genomic, protein expression, and clinical outcome data of patients with SMARCA4 alterations treated at Memorial Sloan Kettering.Results:In 4,813 tumors from patients with NSCLC, we identified 8% (n = 407) of patients with SMARCA4-mutant lung cancer. We describe two categories of SMARCA4 mutations: class 1 mutations (truncating mutations, fusions, and homozygous deletion) and class 2 mutations (missense mutations). Protein expression loss was associated with class 1 mutation (81% vs. 0%, P < 0.001). Both classes of mutation co-occurred more frequently with KRAS, STK11, and KEAP1 mutations compared with SMARCA4 wild-type tumors (P < 0.001). In patients with metastatic NSCLC, SMARCA4 alterations were associated with shorter overall survival, with class 1 alterations associated with shortest survival times (P < 0.001). Conversely, we found that treatment with immune checkpoint inhibitors (ICI) was associated with improved outcomes in patients with SMARCA4-mutant tumors (P = 0.01), with class 1 mutations having the best response to ICIs (P = 0.027).Conclusions:SMARCA4 alterations can be divided into two clinically relevant genomic classes associated with differential protein expression as well as distinct prognostic and treatment implications. Both classes co-occur with KEAP1, STK11, and KRAS mutations, but individually represent independent predictors of poor prognosis. Despite association with poor outcomes, SMARCA4-mutant lung cancers may be more sensitive to immunotherapy.

Purpose:Treatment with PD-(L)1 blockade can produce remarkably durable responses in patients with non–small cell lung cancer (NSCLC). However, a significant fraction of long-term responders ultimately progress and predictors of late progression are unknown. We hypothesized that circulating tumor DNA (ctDNA) analysis of long-term responders to PD-(L)1 blockade may differentiate those who will achieve ongoing benefit from those at risk of eventual progression.Experimental Design:In patients with advanced NSCLC achieving long-term benefit from PD-(L)1 blockade (progression-free survival ≥ 12 months), plasma was collected at a surveillance timepoint late during/after treatment to interrogate ctDNA by Cancer Personalized Profiling by Deep Sequencing. Tumor tissue was available for 24 patients and was profiled by whole-exome sequencing (n = 18) or by targeted sequencing (n = 6).Results:Thirty-one patients with NSCLC with long-term benefit to PD-(L)1 blockade were identified, and ctDNA was analyzed in surveillance blood samples collected at a median of 26.7 months after initiation of therapy. Nine patients also had baseline plasma samples available, and all had detectable ctDNA prior to therapy initiation. At the surveillance timepoint, 27 patients had undetectable ctDNA and 25 (93%) have remained progression-free; in contrast, all 4 patients with detectable ctDNA eventually progressed [Fisher P < 0.0001; positive predictive value = 1, 95% confidence interval (CI), 0.51–1; negative predictive value = 0.93 (95% CI, 0.80–0.99)].Conclusions:ctDNA analysis can noninvasively identify minimal residual disease in patients with long-term responses to PD-(L)1 blockade and predict the risk of eventual progression. If validated, ctDNA surveillance may facilitate personalization of the duration of immune checkpoint blockade and enable early intervention in patients at high risk for progression.

Frequency of altered individual genes within SMARCA4 Class 1 vs SMARCA4 Class 2 subgroups.

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Supplementary Figure S1. ctDNA clonal dynamics during anti-PD1 for patients with a clinical response. Supplementary Figure S2. ctDNA clonal dynamics during anti-PD1 for patients with molecular primary resistance. Supplementary Figure S3. ctDNA molecular responses precede radiologic responses. Supplementary Figure S4. Molecular responses correlate with a favorable prognosis. Supplementary Figure S5. Duration of molecular response correlates with progression-free and overall survival. Supplementary Figure S6. Disease prognostication by radiologic imaging at first assessment. Supplementary Figure S7. Differential clinical outcome by molecular responses in patients with radiologically stable disease. Supplementary Figure S8. Disease prognostication by tumor mutation burden. Supplementary Figure S9. ctDNA molecular response more accurately distinguish clinical responders from non-responders compared to clonal tumor mutation burden. Supplementary Figure S10. Molecular responses mirror pathologic responses to anti-PD1 therapy in early stage operable NSCLC. Supplementary Figure S11. TCR clonal dynamics during response and acquired resistance to anti-PD1. Supplementary Figure S12. TCR clonal dynamics for patients with clinical primary resistance. Supplementary Figure S13. Differential VJ gene usage for a patient with clinical response compared to a patient with clinical primary resistance. Supplementary Figure S14. Dynamic changes in pro-inflammatory and immunosuppressive cytokines in early stage NSCLC patients with differential responses to anti-PD1 therapy.

Purpose:In patients with >1 non–small cell lung carcinoma (NSCLC), the distinction between separate primary lung carcinomas (SPLCs) and intrapulmonary metastases (IPMs) is a common diagnostic dilemma with critical staging implications. Here, we compared the performance of comprehensive next-generation sequencing (NGS) with standard histopathologic approaches for distinguishing NSCLC clonal relationships in clinical practice.Experimental Design:We queried 4,119 NSCLCs analyzed by 341–468 gene MSK-IMPACT NGS assay for patients with >1 surgically resected tumor profiled by NGS. Tumor relatedness predicted by prospective histopathologic assessment was contrasted with comparative genomic profiling by subsequent NGS.Results:Sixty patients with NGS performed on >1 NSCLCs were identified, yielding 76 tumor pairs. NGS classified tumor pairs into 51 definite SPLCs (median, 14; up to 72 unique somatic mutations per pair), and 25 IPMs (24 definite, one high probability; median, 5; up to 16 shared somatic mutations per pair). Prospective histologic prediction was discordant with NGS in 17 cases (22%), particularly in the prediction of IPMs (44% discordant). Retrospective review highlighted several histologic challenges, including morphologic progression in some IPMs. We subsampled MSK-IMPACT data to model the performance of less comprehensive assays, and identified several clinicopathologic differences between NGS-defined tumor pairs, including increased risk of subsequent recurrence for IPMs.Conclusions:Comprehensive NGS allows unambiguous delineation of clonal relationship among NSCLCs. In comparison, standard histopathologic approach is adequate in most cases, but has notable limitations in the recognition of IPMs. Our results support the adoption of broad panel NGS to supplement histology for robust discrimination of NSCLC clonal relationships in clinical practice.

Background Malignant peritoneal mesothelioma (MPeM) is clinically distinct and less studied than malignant pleural mesothelioma. We report the genomic and immunophenotypic features of a prospectively collected MPeM cohort. Methods Next-generation sequencing (NGS) was performed on MPeM tumors. Genomic near-haploidization (GNH) was assessed. WT1, BAP1, mesothelin, VISTA, and PD-L1 were examined by immunohistochemistry (IHC) when tissue was available. Overall survival (OS) was stratified by selected genomic and IHC features. Results Fifty consented patients with MPeM (45 epithelioid, 5 non-epithelioid) demonstrated common alterations in BAP1 (60%; 30/50), NF2 (24%; 12/50) SETD2 (22%; 11/50), and TP53 (16%; 8/50). Seventy-six percent (38/50) of specimens were evaluable for allele-specific copy number analysis; 8% (3/38) had GNH. IHC positivity rates were 93% (37/40) for mesothelin, 96% (46/48) for WT1, 50% (19/38) for PD-L1 and 89% (34/38) for VISTA. BAP1 loss by IHC was observed in 76% (29/38), including five wildtype on NGS. Combining NGS and IHC for BAP1, OS was worse with alteration/loss compared to wildtype/retained in all patients (n=37 vs. 13, 43.8 vs. 117.3 months; p=0.04) Three of thirty patients had a pathogenic germline variant: POT1 I78T, MUTYH R109Y, BAP1 E402*. Conclusion MPeM has a distinct biology and genomic composition. CDKN2A/B alterations were rare in MPeM while BAP1, NF2, TP53, SETD2, LATS2 were common. BAP1 alteration/loss was associated with shorter survival when all patients were included. A notable minority of specimens had GNH associated with NF2, TP53, and SETDB1 mutations. Pathogenic germline mutations were found in 3 of 30 patients.

BACKGROUND: Current risk stratification for patients with malignant pleural mesothelioma based on disease stage and histology is inadequate. For some individuals with early-stage epithelioid tumours, a good prognosis by current guidelines can progress rapidly; for others with advanced sarcomatoid cancers, a poor prognosis can progress slowly. Therefore, we aimed to develop and validate a machine-learning tool—known as OncoCast-MPM—that could create a model for patient prognosis. METHODS: We did a retrospective study looking at malignant pleural mesothelioma tumours using next-generation sequencing from the Memorial Sloan Kettering Cancer Center-Integrated Mutation Profiling of Actionable Cancer Targets (MSK-IMPACT). We collected clinical, pathological, and routine next-generation sequencing data from consecutive patients with malignant pleural mesothelioma treated at the Memorial Sloan Kettering Cancer Center (New York, NY, USA), as well as the MSK-IMPACT data. Together, these data comprised the MSK-IMPACT cohort. Using OncoCast-MPM, an open-source, web-accessible, machine-learning risk-prediction model, we integrated available data to create risk scores that stratified patients into low-risk and high-risk groups. Risk stratification of the MSK-IMPACT cohort was then validated using publicly available malignant pleural mesothelioma data from The Cancer Genome Atlas (ie, the TCGA cohort). FINDINGS: Between Feb 15, 2014, and Jan 28, 2019, we collected MSK-IMPACT data from the tumour tissue of 194 patients in the MSK-IMPACT cohort. The median overall survival was higher in the low-risk group than in the high-risk group as determined by OncoCast-MPM (30·8 months [95% CI 22·7–36·2] vs 13·9 months [10·7–18·0]; hazard ratio [HR] 3·0 [95% CI 2·0–4·5]; p

Malignant pleural diseases, comprising metastatic lung and breast cancers and malignant pleural mesothelioma (MPM), are aggressive solid tumors with poor therapeutic response. We developed and conducted a first-in-human, phase I study of regionally delivered, autologous, mesothelin-targeted chimeric antigen receptor (CAR) T-cell therapy. Intrapleural administration of 0.3M to 60M CAR T cells/kg in 27 patients (25 with MPM) was safe and well tolerated. CAR T cells were detected in peripheral blood for >100 days in 39% of patients. Following our demonstration that PD-1 blockade enhances CAR T-cell function in mice, 18 patients with MPM also received pembrolizumab safely. Among those patients, median overall survival from CAR T-cell infusion was 23.9 months (1-year overall survival, 83%). Stable disease was sustained for ≥6 months in 8 patients; 2 exhibited complete metabolic response on PET scan. Combination immunotherapy with CAR T cells and PD-1 blockade agents should be further evaluated in patients with solid tumors. Significance: Regional delivery of mesothelin-targeted CAR T-cell therapy followed by pembrolizumab administration is feasible, safe, and demonstrates evidence of antitumor efficacy in patients with malignant pleural diseases. Our data support the investigation of combination immunotherapy with CAR T cells and PD-1 blockade agents in solid tumors. See related commentary by Aldea et al., p. 2674. This article is highlighted in the In This Issue feature, p. 2659

To improve understanding of the pathology of immune check-point inhibitor (ICI)-related pneumonitis, clinical, radiographic and histopathological features and outcomes were investigated in a cohort of patients who were treatment-naive before receiving ICI inhibition, who underwent lung biopsy, and in whom other potential causes of lung injury were excluded.Patients were retrospectively identified via searches of institutional pathology and clinical records. Patients treated with other modalities for cancer and patients with lung infections or other aetiologies that could cause pneumonitis were excluded. Clinical records were reviewed by pulmonologists. Imaging studies at presentation and follow-up were reviewed by a thoracic radiologist. Pathology was reviewed by thoracic pathologists.Six patients with ICI-related pneumonitis were identified. Two patients presented with respiratory failure requiring mechanical ventilation, diffuse ground glass opacities (GGOs) on chest computed tomography (CT) and acute lung injury (ALI) pattern on transbronchial lung biopsies and had fatal outcomes, despite treatment. The remaining four patients presented with less severe symptoms, predominantly consolidations and patchy ground glass and part solid opacities on chest CT, organising pneumonia (OP) or chronic interstitial inflammation histologically, and showed favourable responses to treatment and remission within months.This study highlights two radiological-pathological patterns of ICI-related pneumonitis with different behaviour: (1) severe respiratory symptoms and diffuse GGOs on imaging correlating with ALI pattern histologically and poor prognosis; and (2) mild respiratory symptoms and consolidations or patchy subsolid opacities on imaging correlating histologically with OP or chronic interstitial inflammation and good outcomes.

Introduction This study aims to improve understanding of the cytopathology community’s perspective regarding the value of rapid onsite evaluation (ROSE) in clinical practice. Materials and methods The American Society of Cytopathology membership was surveyed in 2019 to obtain subjective data on the cytopathology community’s perceptions regarding ROSE. Comments were categorized by major themes and attitudes and analyzed by respondent’s role in laboratory, practice size, and practice setting (Fisher’s exact and χ2 tests). Results A total of 541 responses were received from 255 cytopathologists/pathologists, 261 cytotechnologists, 19 trainees, and 6 others (as previously reported). Reasons for which cytopathology personnel provide this service aligned with their perceptions of why clinicians request ROSE. A minority of respondents, disproportionally from high volume centers, felt ROSE is unnecessary. Overall attitude regarding ROSE was generally positive. There were no significant differences in attitude regarding ROSE according to role in laboratory or practice size, but respondents from academic centers provided a significantly higher percentage of positive comments than those in private or community practice. Although survey respondents generally felt that ROSE is valuable to patient care, they also highlighted several challenges, including staffing, time commitment, and inadequate reimbursement. Implementation of telecytology was felt to potentially alleviate some of these challenges. Conclusions Survey results show that the cytology community views ROSE favorably, practices vary considerably, and there is a perceived need for improved reimbursement. Data from this study may be used to identify areas that warrant additional research to clarify the clinical value of ROSE.

BACKGROUND: PD-L1 expression is the only FDA-approved biomarker for immune checkpoint inhibitors (ICIs) in patients with lung adenocarcinoma, but sensitivity is modest. Understanding the impact of molecular phenotype, clinical characteristics, and tumor features on PD-L1 expression is largely unknown and may improve prediction of response to ICI. METHODS: We evaluated patients with lung adenocarcinoma in whom PD-L1 testing and targeted next-generation sequencing (MSK-IMPACT) was performed on the same tissue. Clinical and molecular features were compared across PD-L1 subgroups to examine how molecular phenotype associated with tumor PD-L1 expression. In patients treated with anti-PD-(L)1 blockade, we assessed how these interactions impacted efficacy. RESULTS: 1586 patients with lung adenocarcinoma had paired PD-L1 testing and targeted next-generation sequencing. PD-L1 negativity was more common in primary compared to metastatic samples (p

Introduction: Highly aggressive thoracic neoplasms characterized by SMARCA4 (BRG1) deficiency and undifferentiated round cell or rhabdoid morphology have been recently described and proposed to represent thoracic sarcomas. However, it remains unclear whether such tumors may instead represent sarcomatoid carcinomas, and how their clinicopathologic characteristics compare with those of nonsarcomatoid SMARCA4-deficient non–small cell lung carcinomas (SD-NSCC). Methods: We identified 22 SMARCA4-deficient thoracic sarcomatoid tumors (SD-TSTs) with round cell and/or rhabdoid morphology and 45 SD-NSCCs, and comprehensively analyzed their clinicopathologic, immunohistochemical, and genomic characteristics using 341–468 gene next-generation sequencing and other molecular platforms. Results: The relationship of SD-TSTs with NSCC was supported by (1) the presence of NSCC components juxtaposed with sarcomatoid areas in five cases, (2) focal expression of NSCC lineage markers TTF1 or p40 in four additional cases, (3) smoking history in all except one patient (mean = 51 pack-years), accompanied by genomic smoking signature, and (4) high tumor mutation burden (mean = 14.2 mutations per megabase) and mutations characteristic of NSCC in a subset. Compared with SD-NSCCs, SD-TSTs exhibited considerably larger primary tumor size (p < 0.0001), worse survival (p = 0.004), and more frequent presentation at younger age (30–50 years) despite heavier smoking history. Distinctive pathologic features of SD-TSTs included consistent lack of adhesion molecule claudin-4, SMARCA2 (BRM) codeficiency, and frequent expression of stem cell markers. Conclusions: SD-TSTs represent primarily smoking-associated undifferentiated/de-differentiated carcinomas rather than primary thoracic sarcomas. Despite their histogenetic relationship with NSCC, these tumors have unique clinicopathologic characteristics, supporting their recognition as a distinct entity. Further studies are warranted to determine therapeutic approaches to this novel class of exceptionally aggressive thoracic tumors.

Localized malignant mesotheliomas (LMM) is an uncommon and poorly recognized neoplasm. Its pathologic diagnosis is often surprising in patients with serosal/subserosal based localized tumors that are clinically suspicious for metastatic lesions or primary sarcomas. Once a tumor is diagnosed as "mesothelioma", LMM is often mistaken for diffuse malignant mesothelioma (DMM). Best currently available evidence about LMM was collected from the literature and cases diagnosed by members of the International Mesothelioma Panel (IMP). One hundred and one (101) LMM have been reported in the English literature. Patients had localized tumors with identical histopathologic features to DMM. Patients ranged in age from 6 to 82 years; 75% were men. Most (82%) of the tumors were intrathoracic. Others presented as intrahepatic, mesenteric, gastric, pancreatic, umbilical, splenic, and abdominal wall lesions. Tumors varied in size from 0.6 to 15 cm. Most patients underwent surgical resection and/or chemotherapy or radiation therapy. Median survival in a subset of patients was 29 months. Seventy two additional LMM from IMP institutions ranged in age from 28 to 95 years; 58.3% were men. Sixty tumors (83.3%) were intrathoracic, others presented in intraabdominal sites. Tumors varied in size from 1.2 to 19 cm. Median survival for 51 cases was 134 months. Best evidence was used to formulate guidelines for the diagnosis of LMM. It is important to distinguish LMM from DMM as their treatment and prognosis is different. A multidisciplinary approach is needed for the diagnosis of LMM as it shows identical histopathology and immunophenotype to DMM.

Purpose: In patients with >1 non–small cell lung carcinoma (NSCLC), the distinction between separate primary lung carcinomas (SPLCs) and intrapulmonary metastases (IPMs) is a common diagnostic dilemma with critical staging implications. Here, we compared the performance of comprehensive next-generation sequencing (NGS) with standard histopathologic approaches for distinguishing NSCLC clonal relationships in clinical practice. Experimental Design: We queried 4,119 NSCLCs analyzed by 341–468 gene MSK-IMPACT NGS assay for patients with >1 surgically resected tumor profiled by NGS. Tumor relatedness predicted by prospective histopathologic assessment was contrasted with comparative genomic profiling by subsequent NGS. Results: Sixty patients with NGS performed on >1 NSCLCs were identified, yielding 76 tumor pairs. NGS classified tumor pairs into 51 definite SPLCs (median, 14; up to 72 unique somatic mutations per pair), and 25 IPMs (24 definite, one high probability; median, 5; up to 16 shared somatic mutations per pair). Prospective histologic prediction was discordant with NGS in 17 cases (22%), particularly in the prediction of IPMs (44% discordant). Retrospective review highlighted several histologic challenges, including morphologic progression in some IPMs. We subsampled MSK-IMPACT data to model the performance of less comprehensive assays, and identified several clinicopathologic differences between NGS-defined tumor pairs, including increased risk of subsequent recurrence for IPMs. Conclusions: Comprehensive NGS allows unambiguous delineation of clonal relationship among NSCLCs. In comparison, standard histopathologic approach is adequate in most cases, but has notable limitations in the recognition of IPMs. Our results support the adoption of broad panel NGS to supplement histology for robust discrimination of NSCLC clonal relationships in clinical practice.

Substantial changes in the 2021 WHO Classification of Tumors of the Pleura and Pericardium since the 2015 WHO Classification include the following: (1) pleural and pericardial tumors have been combined in one chapter whereas in the 2015 WHO, pericardial tumors were classified with cardiac tumors; (2) well-differentiated papillary mesothelioma has been renamed well-differentiated papillary mesothelial tumor given growing evidence that these tumors exhibit relatively indolent behavior; (3) localized and diffuse mesothelioma no longer include the term "malignant" as a prefix; (4) mesothelioma in situ has been added to the 2021 classification because these lesions can now be recognized by loss of BAP1 and/or MTAP by immunohistochemistry and/or CDKN2A homozygous deletion by fluorescence in situ hybridization; (5) the three main histologic subtypes (i.e., epithelioid, biphasic, and sarcomatoid) remain the same but architectural patterns and cytologic and stromal features are more formally incorporated into the 2021 classification on the basis of their prognostic significance; (6) nuclear grading for epithelioid diffuse mesothelioma is introduced, and it is recommended to record this and other histologically prognostic features in pathology reports; (7) BAP1, EZH2, and MTAP immunohistochemistry have been found to be useful in separating benign mesothelial proliferations from mesothelioma; (8) biphasic mesothelioma can be diagnosed in small biopsies having both epithelioid and sarcomatoid components even if the amount of one component is less than 10%; and (9) the most frequently altered genes in diffuse pleural mesothelioma include BAP1, CDKN2A, NF2, TP53, SETD2, and SETDB1.

Paired T cell receptor and RNA single cell sequencing (scTCR/RNA-seq) has allowed for enhanced resolution of clonal T cell dynamics in cancer. Here, we report a scTCR/RNA-seq dataset of 162,062 single T cells from 31 tissue regions, including tumor, adjacent normal tissues, and lymph nodes (LN), from three patients who underwent resections for progressing lung cancers after immune checkpoint blockade (ICB). We found marked regional heterogeneity in tumor persistence that was associated with heterogeneity in CD4 and CD8 T cell phenotypes; regions with persistent cancer cells were enriched for follicular helper CD4 T cells (TFH), regulatory T cells (Treg), and exhausted CD8 T cells. Clonal analysis demonstrated that highly-expanded T cell clones were predominantly of the CD8 subtype, were ubiquitously present across all sampled regions, found in the peripheral circulation, and expressed gene signatures of ‘large’ and ‘dual-expanded’ clones that have been predictive of response to ICB. Longitudinal tracking of CD8 T cell clones in the peripheral blood revealed that the persistence of ubiquitous CD8 T cell clones, as well as phenotypically distinct clones with tumor-reactive features, correlated with systemic tumor control. Finally, tracking CD8 T cell clones across tissues revealed the presence of TCF-1+precursor exhausted CD8 T cells in tumor draining LNs that were clonally linked to expanded exhausted CD8 T cells in tumors. Altogether, this comprehensive scTCR/RNA-seq dataset with regional, longitudinal, and clonal resolution provides fundamental insights into the tissue distribution, persistence, and differentiation trajectories of ICB-responsive T cells that underlie clinical responses to ICB.

Although cancer immunotherapy with PD-(L)1 blockade is now routine treatment for patients with lung cancer, remarkably little is known about acquired resistance. We examined 1,201 patients with NSCLC treated with PD-(L)1 blockade to clinically characterize acquired resistance, finding it to be common (occurring in more than 60% of initial responders), with persistent but diminishing risk over time, and with distinct metastatic and survival patterns compared to primary resistance. To examine the molecular phenotype and potential mechanisms of acquired resistance, we performed whole transcriptome and exome tumor profiling in a subset of NSCLC patients (n=29) with acquired resistance. Systematic immunogenomic analysis revealed that tumors with acquired resistance generally had enriched signals of inflammation (including IFNγ signaling and inferred CD8+ T cells) and could be separated into IFNγ upregulated and stable subsets. IFNγ upregulated tumors had putative routes of resistance with signatures of dysfunctional interferon signaling and mutations in antigen presentation genes. Transcriptomic profiling of cancer cells from a murine model of acquired resistance to PD-(L)1 blockade also showed evidence of dysfunctional interferon signaling and acquired insensitivity to in vitro interferon gamma treatment. In summary, we characterized clinical and molecular features of acquired resistance to PD-(L)1 blockade in NSCLC and found evidence of ongoing but dysfunctional IFN response. The persistently inflamed, rather than excluded or deserted, tumor microenvironment of acquired resistance informs therapeutic strategies to effectively reprogram and reverse acquired resistance.

Introduction Rapid on-site evaluation (ROSE) is a service provided by cytologists that helps ensure specimen adequacy and appropriate triage for ancillary testing. However, data on the current usage patterns across different practice settings have been lacking. Materials and methods To obtain an accurate and timely assessment of the current state of practice of ROSE, a 14-question online survey was constructed by the Clinical Practice Committee of the American Society for Cytopathology. The survey was available to the membership of the American Society for Cytopathology for a 3-week period in early 2019. Results A total of 541 responses were received, including from 255 cytopathologists/pathologists, 261 cytotechnologists, 19 cytology resident/fellow trainees, and 6 others. ROSE was offered as a clinical service by 95.4% of the respondents, with telecytology for ROSE used in 21.9% of the practices. Endobronchial ultrasound-guided transbronchial needle aspiration was the procedure most frequently reported to use ROSE (mean, 59.1%; median, 70%). Cytotechnologists were involved in ROSE in most practices. The number of daily ROSE procedures correlated with the annual nongynecologic cytology volumes. Approximately 70% of ROSE procedures were reported to require >30 minutes, on average, for the cytologist. Conclusions The results from our survey of cytologists have shown that the reported practice patterns for the usage of ROSE vary considerably. The presented data can help inform future guideline recommendations and the implementation of ROSE in different clinical settings.

Biopsy site changes in mediastinal lymph nodes (LNs) attributable to prior endobronchial ultrasound-guided transbronchial needle aspiration (EBUS-TBNA) have not been studied in a systematic manner. Twenty-four contributors from 14 institutions in 5 countries collaborated via social media (Twitter) to retrospectively review consecutive cases of resected mediastinal LNs from patients with prior EBUS-TBNA. Resected LNs were reexamined by submitting pathologists for changes attributable to EBUS-TBNA. Patients who received neoadjuvant therapy were excluded. Cases with suspected biopsy site changes underwent central review by 5 pathologists. A total of 297 mediastinal LN resection specimens from 297 patients (183 male/114 female, mean age: 65 y, range: 23 to 87) were reviewed. Biopsy site changes were most common in station 7 (10 cases) followed by 11R, 4R, and 10R, and were found in 34/297 (11.4%) cases, including displacement of tiny cartilage fragments into LN parenchyma in 26, intranodal or perinodal scars in 7, and hemosiderin in 1. Cartilage fragments ranged from 0.26 to 1.03 mm in length and 0.18 to 0.62 mm in width. The mean interval between EBUS-TBNA and LN resection was 38 days (range: 10 to 112) in cases with biopsy site changes. A control group of 40 cases without prior EBUS-TBNA, including 193 mediastinal LN stations, showed no evidence of biopsy site changes. Biopsy site changes are identified in a subset of resected mediastinal LNs previously sampled by EBUS-TBNA. The location of the abnormalities, temporal association with prior EBUS-TBNA, and the absence of such findings in cases without prior EBUS-TBNA support the contention that they are caused by EBUS-TBNA.

Despite the initial successes of immunotherapy, there is an urgent clinical need for molecular assays that identify patients more likely to respond. Here, we report that ultrasensitive measures of circulating tumor DNA (ctDNA) and T-cell expansion can be used to assess responses to immune checkpoint blockade in metastatic lung cancer patients (N = 24). Patients with clinical response to therapy had a complete reduction in ctDNA levels after initiation of therapy, whereas nonresponders had no significant changes or an increase in ctDNA levels. Patients with initial response followed by acquired resistance to therapy had an initial drop followed by recrudescence in ctDNA levels. Patients without a molecular response had shorter progression-free and overall survival compared with molecular responders [5.2 vs. 14.5 and 8.4 vs. 18.7 months; HR 5.36; 95% confidence interval (CI), 1.57–18.35; P = 0.007 and HR 6.91; 95% CI, 1.37–34.97; P = 0.02, respectively], which was detected on average 8.7 weeks earlier and was more predictive of clinical benefit than CT imaging. Expansion of T cells, measured through increases of T-cell receptor productive frequencies, mirrored ctDNA reduction in response to therapy. We validated this approach in an independent cohort of patients with early-stage non–small cell lung cancer (N = 14), where the therapeutic effect was measured by pathologic assessment of residual tumor after anti-PD1 therapy. Consistent with our initial findings, early ctDNA dynamics predicted pathologic response to immune checkpoint blockade. These analyses provide an approach for rapid determination of therapeutic outcomes for patients treated with immune checkpoint inhibitors and have important implications for the development of personalized immune targeted strategies. Significance: Rapid and sensitive detection of circulating tumor DNA dynamic changes and T-cell expansion can be used to guide immune targeted therapy for patients with lung cancer. See related commentary by Zou and Meyerson, p. 1038

Background: Despite recent treatment advances, malignant pleural mesothelioma (MPM) is an aggressive, recalcitrant malignancy. Currently, histologic subtype (epithelioid/non-epithelioid/biphasic) is the primary prognostic factor; other potential biomarkers to guide therapeutic strategies remain elusive. Even with multimodality therapies, recurrence is high in early-stage disease. In the unresectable/metastatic setting, there are only two FDA approved regimens, both in the first line setting: cisplatin/pemetrexed and ipilimumab/nivolumab. Unfortunately, most who respond to first line treatment experience disease progression within a year. A few established MPM cell lines, with inherent limitations, provide minimal preclinical insight. The relative lack of model systems that accurately reflect MPM tumorigenesis is a barrier to therapeutic and diagnostic advances in MPM. Methods: We developed a diverse library of 22 extensively annotated patient-derived xenograft (PDX) models from 22 patients with MPM. Multi-omic analyses including, targeted tumor next-generation sequencing by MSK-IMPACT, RNA-sequencing, and immunohistochemistry was performed. We deconvoluted the mutational landscapes, global expression profiles, and molecular subtypes of these MPM models and further compared the PDXs to MPM clinical specimens, including matched PDX and primary tumor pairs. Results: The mutational landscapes of PDX models strongly correlated with paired tumor samples. There were some differences in CDKN2A/B mutations and relative enrichment of NF2 with fewer BAP1 alterations, the significance of which is being investigated. When compared by histological subtype, we observed an upregulation of genes involved in NOTCH and EMT signaling in the epithelioid models. Models derived from patients with shorter overall survival or poor response to platinum doublet had higher expression of WNT/β-catenin signaling, hedgehog pathway, and epithelial-mesenchymal transition signaling as well as downregulation of immune-activation pathways, including type I and II interferon signaling and inflammatory response pathways. Conclusions: This library of MPM PDXs, the largest to date, effectively mimics human disease and provides unprecedented insight into the genomic, transcriptomic, and protein landscape of MPM. These PDX models will inform future clinical investigations and provide an important new preclinical resource. Citation Format: Michael Offin, Jennifer L. Sauter, Jacklyn V. Egger, Elisa deStanchina, John T. Poirier, Marjorie G. Zauderer, Charles Rudin, Triparna Sen. Multiomic profiling of patient-derived xenografts established from patients with malignant pleural mesothelioma proposes pathways associated with poor prognosis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 51.

We studied the suitability of commercially available monoclonal antibodies (mAbs) for the immunohistochemical (IHC) detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV2) in standard archival specimens. Antibodies were screened on HEK293 cells transfected with viral nucleoprotein, S1 subunit and S2 subunit of spike protein and on untransfected cells, as well as a panel of normal tissue. Lung tissue with presence of SARS-CoV2 confirmed by in situ hybridization (ISH) was also used. A total of 7 mAbs were tested: (1) mAb 001 (Sino Biological, 40143-R001), (2) mAb 007 (Sino Biological, 40150-R007), (3) mAb 019 (Sino Biological, 40143-R019), (4) mAb 1A9 (GeneTex, GTX632604), (5) mAb ABM19C9 (Abeomics, 10-10007), (6) FIPV3-70 (Santa Cruz, SC-65653), and (7) mAb 6F10 (BioVision, A2060). Only 2 mAbs, clone 001 to the nucleoprotein and clone 1A9 to the S2 subunit spike protein displayed specific immunoreactivity. Both clones showed strong staining in the acute phase of COVID-19 pneumonia, mostly in areas of acute diffuse alveolar damage, but were not completely congruent. Viral protein was also found in kidney tubules, endothelia of multiple organs and a nasal swab of a patient with persistent SARS-CoV2 infection. The other tested reagents were either poorly reactive or demonstrated nonspecific staining in tissues and lesions not infected by SARS-CoV2. Our study demonstrates that rigid specificity testing is mandatory for the evaluation of mAbs to SARS-CoV2 and that clones 001 to nucleoprotein and 1A9 to S2 subunit spike protein are useful for the in situ detection of SARS-CoV2.

Introduction Recent studies have identified subtypes of small cell lung carcinoma (SCLC) defined by the RNA expression of ASCL1, NEUROD1, POU2F3, and YAP1 transcriptional regulators. There are only limited data on the distribution of these markers at the protein level and associated pathologic characteristics in clinical SCLC samples. Methods The expression of ASCL1, NEUROD1, POU2F3, and YAP1 was analyzed by immunohistochemistry in 174 patient samples with SCLC. Subtypes defined by these markers were correlated with histologic characteristics, expression of classic neuroendocrine markers (synaptophysin, chromogranin A, CD56, INSM1), and other SCLC markers, including the neuroendocrine phenotype-associated markers TTF-1 and DLL3. Results ASCL1 and NEUROD1 expression had the following distribution: (1) 41% ASCL1+/NEUROD1−; (2) 37% ASCL1+/NEUROD1+; (3) 8% ASCL1−/NEUROD1+; and (4) 14% ASCL1−/NEUROD1−. On the basis of their relative expression, 69% of cases were ASCL1-dominant and 17% were NEUROD1-dominant. POU2F3 was expressed in 7% of SCLC and was mutually exclusive of ASCL1 and NEUROD1. YAP1 was expressed at low levels, primarily in combined SCLC, and was not exclusive of other subtypes. Both ASCL1-dominant and NEUROD1-dominant subtypes were associated with neuroendocrine markerhigh/TTF-1high/DLL3high profile, whereas POU2F3 and other ASCL1/NEUROD1 double-negative tumors were neuroendocrine markerlow/TTF-1low/DLL3low. Conclusions This is the first comprehensive immunohistochemical and histopathologic analysis of novel SCLC subtypes in patient samples. We confirm that ASCL1/NEUROD1 double-negative tumors represent a distinct neuroendocrine-low subtype of SCLC, which is either uniquely associated with POU2F3 or lacks a known dominant regulator. The expression profiles of these markers appear more heterogeneous in native samples than in experimental models, particularly with regard to the high prevalence of ASCL1/NEUROD1 coexpression. These findings may have prognostic and therapeutic implications and warrant further clinical investigation.

Remote digital pathology allows healthcare systems to maintain pathology operations during public health emergencies. Existing Clinical Laboratory Improvement Amendments regulations require pathologists to electronically verify patient reports from a certified facility. During the 2019 pandemic of COVID-19 disease, caused by the SAR-CoV-2 virus, this requirement potentially exposes pathologists, their colleagues, and household members to the risk of becoming infected. Relaxation of government enforcement of this regulation allows pathologists to review and report pathology specimens from a remote, non-CLIA certified facility. The availability of digital pathology systems can facilitate remote microscopic diagnosis, although formal comprehensive (case-based) validation of remote digital diagnosis has not been reported. All glass slides representing routine clinical signout workload in surgical pathology subspecialties at Memorial Sloan Kettering Cancer Center were scanned on an Aperio GT450 at ×40 equivalent resolution (0.26 µm/pixel). Twelve pathologists from nine surgical pathology subspecialties remotely reviewed and reported complete pathology cases using a digital pathology system from a non-CLIA certified facility through a secure connection. Whole slide images were integrated to and launched within the laboratory information system to a custom vendor-agnostic, whole slide image viewer. Remote signouts utilized consumer-grade computers and monitors (monitor size, 13.3–42 in.; resolution, 1280 × 800–3840 × 2160 pixels) connecting to an institution clinical workstation via secure virtual private network. Pathologists subsequently reviewed all corresponding glass slides using a light microscope within the CLIA-certified department. Intraobserver concordance metrics included reporting elements of top-line diagnosis, margin status, lymphovascular and/or perineural invasion, pathology stage, and ancillary testing. The median whole slide image file size was 1.3 GB; scan time/slide averaged 90 s; and scanned tissue area averaged 612 mm2. Signout sessions included a total of 108 cases, comprised of 254 individual parts and 1196 slides. Major diagnostic equivalency was 100% between digital and glass slide diagnoses; and overall concordance was 98.8% (251/254). This study reports validation of primary diagnostic review and reporting of complete pathology cases from a remote site during a public health emergency. Our experience shows high (100%) intraobserver digital to glass slide major diagnostic concordance when reporting from a remote site. This randomized, prospective study successfully validated remote use of a digital pathology system including operational feasibility supporting remote review and reporting of pathology specimens, and evaluation of remote access performance and usability for remote signout.

INTRODUCTION: Histologic subtypes of malignant pleural mesothelioma are a major prognostic indicator and decision denominator for all therapeutic strategies. In an ambiguous case, a rare transitional mesothelioma (TM) pattern may be diagnosed by pathologists either as epithelioid mesothelioma (EM), biphasic mesothelioma (BM), or sarcomatoid mesothelioma (SM). This study aimed to better characterize the TM subtype from a histological, immunohistochemical, and molecular standpoint. Deep learning of pathologic slides was applied to this cohort. METHODS: A random selection of 49 representative digitalized sections from surgical biopsies of TM was reviewed by 16 panelists. We evaluated BAP1 expression and CDKN2A (p16) homozygous deletion. We conducted a comprehensive, integrated, transcriptomic analysis. An unsupervised deep learning algorithm was trained to classify tumors. RESULTS: The 16 panelists recorded 784 diagnoses on the 49 cases. Even though a Kappa value of 0.42 is moderate, the presence of a TM component was diagnosed in 51%. In 49% of the histological evaluation, the reviewers classified the lesion as EM in 53%, SM in 33%, or BM in 14%. Median survival was 6.7 months. Loss of BAP1 observed in 44% was less frequent in TM than in EM and BM. p16 homozygous deletion was higher in TM (73%), followed by BM (63%) and SM (46%). RNA sequencing unsupervised clustering analysis revealed that TM grouped together and were closer to SM than to EM. Deep learning analysis achieved 94% accuracy for TM identification. CONCLUSION: These results revealed that the TM pattern should be classified as non-EM or at minimum as a subgroup of the SM type. ispartof: JOURNAL OF THORACIC ONCOLOGY vol:15 issue:6 pages:1037-1053 ispartof: location:United States status: published

PURPOSE: SMARCA4 mutations are among the most common recurrent alterations in NSCLC, but the relationship to other genomic abnormalities and clinical impact has not been established. EXPERIMENTAL DESIGN: To characterize SMARCA4 alterations in NSCLC, we analyzed the genomic, protein expression, and clinical outcome data of patients with SMARCA4 alterations treated at Memorial Sloan Kettering. RESULTS: In 4813 tumors from patients with NSCLC, we identified 8% (n= 407) patients with SMARCA4-mutant lung cancer. We describe two categories of SMARCA4 mutations: Class 1 mutations (truncating mutations, fusions and homozygous deletion) and Class 2 mutations (missense mutations). Protein expression loss was associated with Class 1 mutation (81% vs 0%, (P < 0.001)). Both classes of mutation co-occured more frequently with KRAS, STK11, and KEAP1 mutations compared to SMARCA4 wildtype tumors (P < 0.001). In patients with metastatic NSCLC, SMARCA4 alterations were associated with shorter overall survival, with Class 1 alterations associated with shortest survival times (P < 0.001). Conversely, we found that treatment with immune checkpoint inhibitors was associated with improved outcomes in patients with SMARCA4-mutant tumors (P = 0.01), with Class 1 mutations having the best response to ICIs (p = 0.027). CONCLUSIONS: SMARCA4 alterations can be divided into two clinically relevant genomic classes associated with differential protein expression as well as distinct prognostic and treatment implications. Both classes co-occur with KEAP1, STK11, and KRAS mutations, but individually represent independent predictors of poor prognosis. Despite association with poor outcomes, SMARCA4-mutant lung cancers may be more sensitive to immunotherapy.

Purpose: Treatment with PD-(L)1 blockade can produce remarkably durable responses in patients with non–small cell lung cancer (NSCLC). However, a significant fraction of long-term responders ultimately progress and predictors of late progression are unknown. We hypothesized that circulating tumor DNA (ctDNA) analysis of long-term responders to PD-(L)1 blockade may differentiate those who will achieve ongoing benefit from those at risk of eventual progression. Experimental Design: In patients with advanced NSCLC achieving long-term benefit from PD-(L)1 blockade (progression-free survival ≥ 12 months), plasma was collected at a surveillance timepoint late during/after treatment to interrogate ctDNA by Cancer Personalized Profiling by Deep Sequencing. Tumor tissue was available for 24 patients and was profiled by whole-exome sequencing (n = 18) or by targeted sequencing (n = 6). Results: Thirty-one patients with NSCLC with long-term benefit to PD-(L)1 blockade were identified, and ctDNA was analyzed in surveillance blood samples collected at a median of 26.7 months after initiation of therapy. Nine patients also had baseline plasma samples available, and all had detectable ctDNA prior to therapy initiation. At the surveillance timepoint, 27 patients had undetectable ctDNA and 25 (93%) have remained progression-free; in contrast, all 4 patients with detectable ctDNA eventually progressed [Fisher P < 0.0001; positive predictive value = 1, 95% confidence interval (CI), 0.51–1; negative predictive value = 0.93 (95% CI, 0.80–0.99)]. Conclusions: ctDNA analysis can noninvasively identify minimal residual disease in patients with long-term responses to PD-(L)1 blockade and predict the risk of eventual progression. If validated, ctDNA surveillance may facilitate personalization of the duration of immune checkpoint blockade and enable early intervention in patients at high risk for progression.