Comparison of Immunohistochemistry, Next-generation Sequencing and Fluorescence In Situ Hybridization for Detection of MTAP Loss in Pleural Mesothelioma.

9p21 deletions involving MTAP/CDKN2A genes are detected in diffuse pleural mesotheliomas (DPM) but are absent in benign mesothelial proliferations. Loss of MTAP expression by immunohistochemistry (IHC) is well accepted as a surrogate for 9p21 deletion to support a diagnosis of DPM. Accurate interpretation can be critical in the diagnosis of DPM, but variations in antibody performance may impact interpretation. The objectives of this study were to compare the performance of MTAP monoclonal antibodies (mAbs) EPR6893 and 1813 and to compare MTAP expression by IHC with 9p21 copy number status in DPM. Cytoplasmic expression of MTAP IHC with mAbs EPR6893 (ab126770; Abcam) and 1813 (NBP2-75730, Novus Biologicals) was evaluated in 56 DPM (47 epithelioid, 7 biphasic, and 2 sarcomatoid) profiled by targeted next-generation sequencing. 9p21 Copy number status was assessed by Fraction and Allele-Specific Copy Number Estimates from Tumor Sequencing (FACETS) analysis and also by CDKN2A fluorescence in situ hybridization in discrepant cases when material was available. MTAP mAb 1813 showed stronger immunoreactivity, more specific staining, and no equivocal interpretations compared to mAb EPR6893 which showed equivocal staining in 19 (34%) of cases due to weak or heterogenous immunoreactivity, lack of definitive internal positive control, and/or nonspecific background staining. MTAP expression with mAb 1813 showed near perfect agreement with 9p21 copy number by combined FACETS/fluorescence in situ hybridization calls (κ = 0.85; 95% CI, 0.71-0.99; P < .001). MTAP IHC with mAb 1813 was 96% sensitive, 86% specific, and 93% accurate for 9p21 homozygous deletion. The findings of this study suggest that interpretation of MTAP IHC is improved with mAb 1813 because mAb EPR6893 was often limited by equivocal interpretations. We show that MTAP IHC and molecular assays are complementary in detecting 9p21 homozygous deletion. MTAP IHC may be particularly useful for low tumor purity samples and in low-resource settings.

Clinical Characteristics and Outcomes of Patients with Well-Differentiated Papillary Peritoneal Mesothelial Tumors.

PURPOSE: Well-differentiated papillary peritoneal mesothelial tumors (WDPMTs) are understudied and discrete from peritoneal mesotheliomas (PMs). We report clinicopathologic characteristics and outcomes of a large prospective WDPMT cohort. METHODS: Patients with WDPMT identified between August 2007 and December 2020 were followed through January 2023. Clinical characteristics and outcomes were annotated. Overall survival (OS) was assessed from pathologic diagnosis. Germline variants were analyzed, and targeted next-generation sequencing (NGS; MSK-IMPACT) data were compared to PMs and diffuse pleural mesotheliomas (DPMs). RESULTS: Among 54 patients, median age at diagnosis was 55 (range 20-76), 50% were female (n = 27), and 46% were smokers (n = 25; median 8 pack/years). Most (94%, n = 51) WDPMTs were found during surgical explorations for other indications, primarily other malignancies. Two patients underwent surgical resection for WDPMT; none received systemic therapy for WDPMT. Median OS was not reached (19/54; median follow up 4.5 years). Somatic NGS was available for 35% (19/54) of patients. TRAF7 alterations were enriched in WDPMT (89%; 17/19) compared with PM (0%; 0/50; p < 0.0001) and DPM (0%; 0/74; p < 0.0001). In WDPMT compared with PM and DPM, there were less BAP1 (0% [0/0] vs. 4% [8/50] vs. 46% [34/74]; p = 0.001 and p < 0.0001, respectively) and NF2 (0% [0/0] vs. 24% [12/50] vs. 31% [23/74]; p = 0.03 and p = 0.001 respectively) alterations. Pathogenic germline variants were present in 23% (4/17) of WDPMTs. CONCLUSIONS: Well-differentiated papillary peritoneal mesothelial tumors were primarily incidental findings. There was no WDPMT-related mortality, so there was no distinct role for routine cytoreductive surgery or systemic therapy. Genomic profiles can help to differentiate WDPMT from DPM and PM.

Neurofibromatosis Type 2-Yes-Associated Protein and Transcriptional Coactivator With PDZ-Binding Motif Dual Immunohistochemistry Is a Reliable Marker for the Detection of Neurofibromatosis Type 2 Alterations in Diffuse Pleural Mesothelioma.

Neurofibromatosis type 2 (NF2) loss occurs in approximately 30% to 50% of diffuse pleural mesothelioma (DPM) with accumulation of yes-associated protein (YAP) 1 and transcriptional coactivator with PDZ-binding motif (TAZ) in tumor nuclei. NF2 and YAP/TAZ represent potential therapeutic targets. We investigated the performance of NF2-YAP/TAZ dual immunohistochemistry (IHC) in identifying DPM that harbors NF2 alterations and in distinguishing DPM from benign mesothelial proliferations. NF2-YAP/TAZ IHC was subsequently performed in a Discovery cohort of DPMs with (n = 10) or without (n = 10) NF2 alterations detected by next-generation sequencing (NGS) and 9 benign cases. The cutoff values for loss of NF2 expression and YAP/TAZ overexpression using IHC were determined in the Discovery cohort. The performance characteristics of NF2-YAP/TAZ IHC were investigated in a Validation cohort (20 DPMs and 10 benign cases). In the Discovery cohort, all DPMs with NF2 alterations using NGS showed NF2 IHC scores of <2, whereas all NF2-wild-type DPMs showed scores of ≥2. NF2-altered DPMs had significantly higher YAP/TAZ H-scores (P < .001) than NF2-wild-type DPM and benign pleura (median H-scores: 237.5 [range, 185-275], 130.0 [range, 40-225], and 10.0 [range, 0-75], respectively). NF2-YAP/TAZ IHC demonstrated 95.2% sensitivity, 100% specificity, 100% positive predictive value, and 95% negative predictive value for detecting NF2 alterations in DPM (n = 40) with NGS as the gold standard and 87.5% sensitivity and 100% specificity for distinguishing DPM (n = 40) from benign mesothelial proliferations (n = 19). NF2-YAP/TAZ IHC has a high sensitivity and specificity for detecting NF2 alterations in DPM and a high specificity for malignancy, highlighting potential utility for guiding NF2-targeted therapies and distinguishing DPM from benign mimics.

Immune check-point inhibitor-related pneumonitis: acute lung injury with rapid progression and organising pneumonia with less severe clinical disease.

AIMS: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.

V-domain Ig-containing suppressor of T-cell activation (VISTA), a potentially targetable immune checkpoint molecule, is highly expressed in epithelioid malignant pleural mesothelioma.

V-domain Ig-containing suppressor of T-cell activation (VISTA) is an immune checkpoint gene that inhibits anti-tumor immune responses. Since most malignant pleural mesotheliomas do not respond to anti-programmed cell death(-ligand)1 (PD-(L)1)/cytotoxic T-lymphocyte-associated protein 4 (CTLA4) therapy and given the recent finding of The Cancer Genome Atlas Study that pleural mesothelioma displays the highest expression of VISTA among all cancers studied, we examined VISTA expression in a large pleural mesothelioma cohort. VISTA and PD-L1 immunohistochemistry were performed on tissue microarray of immunotherapy-naive pleural mesotheliomas (254 epithelioid, 24 biphasic and 41 sarcomatoid) and ten whole-tissue sections of benign pleura (VISTA only). Percentages of tumor and inflammatory cells with positive staining were assessed. Optimal prognostic cutoff percentages were determined using maximally selected rank statistics. Overall survival was evaluated using Kaplan-Meier methods and Cox proportional hazard analysis. All benign mesothelium expressed VISTA. Eighty-five percent of 319 and 38% of 304 mesotheliomas expressed VISTA and PD-L1 (88% and 33% of epithelioid, 90% and 43% of biphasic, and 42% and 75% of sarcomatoid), respectively. Median VISTA score was significantly higher in epithelioid (50%) (vs. biphasic [20%] and sarcomatoid [0]) (p < 0.001), while median PD-L1 score was significantly higher in sarcomatoid tumors (20%) (vs. biphasic and epithelioid [both 0%]) (p < 0.001). VISTA and PD-L1 were expressed in inflammatory cells in 94% (n = 317) and 24% (n = 303) of mesothelioma, respectively. Optimal prognostic cutoffs for VISTA and PD-L1 were 40% and 30%, respectively. On multivariable analysis, VISTA and PD-L1 expression in mesothelioma were associated with better and worse overall survival (p = 0.001 and p = 0.002), respectively, independent of histology. In a large cohort of mesothelioma, we report frequent expression of VISTA and infrequent expression of PD-L1 with favorable and unfavorable survival correlations, respectively. These findings may explain poor responses to anti-PD-(L)1 immunotherapy and suggest VISTA as a potential novel target in pleural mesothelioma.

Validation of a digital pathology system including remote review during the COVID-19 pandemic.

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.

Insights into pathogenesis of fatal COVID-19 pneumonia from histopathology with immunohistochemical and viral RNA studies.

INTRODUCTION: We describe post-mortem pulmonary histopathologic findings of COVID-19 pneumonia in patients with a spectrum of disease course, from rapid demise to prolonged hospitalisation. METHODS AND RESULTS: Histopathologic findings in post-mortem lung tissue from eight patients who died from COVID-19 pneumonia were reviewed. Immunohistochemistry (IHC) and next-generation sequencing (NGS) were performed to detect virus. Diffuse alveolar damage (DAD) was seen in all cases with a spectrum of acute phase and/or organising phase. IHC with monoclonal antibodies against SARS-CoV-2 viral nucleoprotein and spike protein detected virus in areas of acute but not organising DAD, with intracellular viral antigen and RNA expression seen predominantly in patients with duration of illness less than 10 days. Major vascular findings included thrombi in medium- and large-calibre vessels, platelet microthrombi detected by CD61 IHC and fibrin microthrombi. CONCLUSIONS: Presence of SARS-CoV-2 viral RNA by NGS early in the disease course and expression of viral antigen by IHC exclusively in the acute, but not in the organising phase of DAD, suggests that the virus may play a major role in initiating the acute lung injury of DAD, but when DAD progresses to the organising phase the virus may have been cleared from the lung by the patient's immune response. These findings suggest the possibility of a major change during the disease course of COVID-19 pneumonia that may have therapeutic implications. Frequent thrombi and microthrombi may also present potential targets for therapeutic intervention.

Nuclear grade and necrosis predict prognosis in malignant epithelioid pleural mesothelioma: a multi-institutional study.

A recently described nuclear grading system predicted survival in patients with epithelioid malignant pleural mesothelioma. The current study was undertaken to validate the grading system and to identify additional prognostic factors. We analyzed cases of epithelioid malignant pleural mesothelioma from 17 institutions across the globe from 1998 to 2014. Nuclear grade was computed combining nuclear atypia and mitotic count into a grade of I-III using the published system. Nuclear grade was assessed by one pathologist for three institutions, the remaining were scored independently. The presence or absence of necrosis and predominant growth pattern were also evaluated. Two additional scoring systems were evaluated, one combining nuclear grade and necrosis and the other mitotic count and necrosis. Median overall survival was the primary endpoint. A total of 776 cases were identified including 301 (39%) nuclear grade I tumors, 354 (45%) grade II tumors and 121 (16%) grade III tumors. The overall survival was 16 months, and correlated independently with age (P=0.006), sex (0.015), necrosis (0.030), mitotic count (0.001), nuclear atypia (0.009), nuclear grade (<0.0001), and mitosis and necrosis score (<0.0001). The addition of necrosis to nuclear grade further stratified overall survival, allowing classification of epithelioid malignant pleural mesothelioma into four distinct prognostic groups: nuclear grade I tumors without necrosis (29 months), nuclear grade I tumors with necrosis and grade II tumors without necrosis (16 months), nuclear grade II tumors with necrosis (10 months) and nuclear grade III tumors (8 months). The mitosis-necrosis score stratified patients by survival, but not as well as the combination of necrosis and nuclear grade. This study confirms that nuclear grade predicts survival in epithelioid malignant pleural mesothelioma, identifies necrosis as factor that further stratifies overall survival, and validates the grading system across multiple institutions and among both biopsy and resection specimens. An alternative scoring system, the mitosis-necrosis score is also proposed.

SMARCA4-deficient thoracic sarcoma: a distinctive clinicopathological entity with undifferentiated rhabdoid morphology and aggressive behavior.

A distinct subset of thoracic sarcomas with undifferentiated rhabdoid morphology and SMARCA4 inactivation has recently been described, and potential targeted therapy for SMARC-deficient tumors is emerging. We sought to validate the clinicopathological features of SMARCA4-deficient thoracic sarcomas. Clinicopathological information was gathered for 40 undifferentiated thoracic tumors with rhabdoid morphology (mediastinum (n=18), lung (n=14), pleura (n=8)). Thymic carcinomas (n=11) were used as a comparison group. Immunohistochemistry included BRG1 (SMARCA4), BRM (SMARCA2), INI-1 (SMARCB1), pan-cytokeratin, desmin, NUT, S-100 protein, TTF1, CD34, and SOX2. BRG1 loss was present in 12 of 40 rhabdoid thoracic tumors (30%): 7 of 18 in mediastinum (39%), 2 of 8 in pleura (25%), and 3 of 14 in lung (21%). All BRG1-deficient tumors tested for BRM (n=8) showed concomitant loss. All thymic carcinomas showed retained BRG1 and INI-1. Morphologically, tumors with BRG1 loss showed sheets of monotonous ovoid cells with indistinct cell borders, abundant eosinophilic cytoplasm, and prominent nucleoli. Scattered areas with rhabdoid morphology (ie, eccentric nuclei, dense eosinophilic cytoplasm, discohesion) were present in all the cases. SMARCA4/BRG1-deficient sarcomas showed rare cells positive for cytokeratin in 10 cases (83%). One showed rare TTF1-positive cells. All were negative for desmin, NUT, and S-100 protein. CD34 was positive in three of five (60%) BRG1-deficient tumors tested. SOX2 was positive in all four BRG1-deficient tumors tested, and negative in all seven tested cases with retained BRG1. SMARCA4/BRG1-deficient sarcomas occurred at median age of 59 years (range 44-76) with male predominance (9:3) and had worse 2-year survival compared with BRG1-retained tumors (12.5% vs 64.4%, P=0.02). SMARCA4-deficient thoracic sarcomas can be identified based on their distinctive high-grade rhabdoid morphology, and the diagnosis can be confirmed by immunohistochemistry. Identification of these tumors is clinically relevant due to their aggressive behavior, poor prognosis, and potential targeted therapy.

Pathological findings in spontaneous pneumothorax specimens: does the incidence of unexpected clinically significant findings justify routine histological examination?

AIMS: The utility of routine histological examination of clinically primary spontaneous pneumothorax (SPTX) specimens has been questioned. In this retrospective study, we aimed to assess the clinical significance of unexpected SPTX histopathological findings, to determine whether such findings justify routine histological examination of SPTX specimens. METHODS AND RESULTS: Records and slides from all SPTX resections at our institution from 2002-2012 were reviewed. Clinically significant unexpected histological findings were identified in 8.3% of 72 patients, including: one patient with lung cancer, one with endometriosis, one with Birt-Hogg-Dubé (BHD) syndrome, and three with 'bong lung'. Detection of BHD syndrome has the potential to avert advanced renal carcinoma by identifying individuals who should undergo periodic abdominal CT screening. The cost of treating a case of advanced renal carcinoma far exceeds that of histologically examining all SPTX specimens received in a 10-year period at our institution. CONCLUSIONS: Gross examination alone is an inadequate evaluation of SPTX specimens. This is the first study to demonstrate that routine histological examination of SPTX specimens is justified, in that it discloses unexpected findings that are clinically significant and impact on patient management.

Testing of integrated human papillomavirus mRNA decreases colposcopy referrals: could a change in human papillomavirus detection methodology lead to more cost-effective patient care?

OBJECTIVES: This study investigates potential colposcopy referral rates, as per the latest American Society for Colposcopy and Cervical Pathology recommendations, following the change in high-risk human papillomavirus (HR-HPV) detection methodology from Hybrid Capture 2 (HC2) to APTIMA at our institution. STUDY DESIGN: Rates of colposcopy referral were compared between two cohorts, each comprising all Pap samples with a diagnosis of atypical squamous cells of undetermined significance (ASCUS) tested for HR-HPV in our laboratory during a 12-month period. Cohorts I and II included Pap samples tested with HC2 (n = 1,856) and APTIMA (n = 1,651), respectively. The rates of quantity not sufficient (QNS) results were determined for all Pap samples during the same time periods. RESULTS: The proportion of HR-HPV-positive Pap samples with an ASCUS diagnosis was significantly lower with APTIMA (42%) than with HC2 (53%; p < 0.0001). APTIMA also resulted in a significantly lower QNS rate among all Pap samples (0.42 vs. 4.3% with HC2; p < 0.0001). CONCLUSION: The change in HR-HPV detection methodology from HC2 to APTIMA has led to a 21% reduction in colposcopy referrals and a 90% decrease in QNS rates at our institution. The new methodology has resulted in more cost-effective patient care and fewer insufficient samples requiring repeat HR-HPV testing.

Diffuse Pleural Mesothelioma: Advances in Molecular Pathogenesis, Diagnosis, and Treatment.

Diffuse pleural mesothelioma (DPM) is a highly aggressive malignant neoplasm arising from the mesothelial cells lining the pleural surfaces. While DPM is a well-recognized disease linked to asbestos exposure, recent advances have expanded our understanding of molecular pathogenesis and transformed our clinical practice. This comprehensive review explores the current concepts and emerging trends in DPM, including risk factors, pathobiology, histologic subtyping, and therapeutic management, with an emphasis on a multidisciplinary approach to this complex disease.

Diffuse Pleural Mesotheliomas with Genomic Near-Haploidization: A Newly Recognized Subset with Distinct Clinical, Histologic, and Molecular Features.

PURPOSE: Diffuse pleural mesotheliomas (DPM) with genomic near-haploidization (GNH) represent a novel subtype first recognized by The Cancer Genome Atlas project; however, its clinicopathologic and molecular features remain poorly defined. EXPERIMENTAL DESIGN: We analyzed clinical genomic profiling data from 290 patients with DPM using the Memorial Sloan Kettering-Integrated Mutation Profiling of Actionable Cancer Targets (MSK-IMPACT) assay. Allele-specific copy number analysis was performed using the Fraction and Allele-Specific Copy Number Estimates from Tumor Sequencing (FACETS) algorithm. RESULTS: A total of 210 patients were evaluable for loss of heterozygosity (LOH) analysis using FACETS from MSK-IMPACT tumor:normal sequencing data. In this cohort, GNH, defined as LOH across >80% of the genome, was detected in 10 cases (4.8%). Compared with non-GNH tumors, GNH DPMs were associated with younger age and less frequent self-reported history of occupational asbestos exposure. Histologically, GNH DPMs were enriched in biphasic subtype (80% vs. 14.5%) and showed abundant tumor-infiltrating lymphocytes (TILs). Genomic analysis revealed a higher frequency of TP53 alterations, whereas SETDB1 mutations were present in nearly all and only in this subset. The clinicopathologic and molecular findings were further validated in a separate cohort. Despite the younger age, patients with GNH DPMs had a shorter overall survival (10.9 vs. 25.4 months, P = 0.004); the poor prognostic impact of GNH remained significant after controlling for biphasic histology. Of three patients with GNH DPMs who received immune checkpoint blockade, two achieved a clinician-assessed partial response. CONCLUSIONS: GNH defines an aggressive subtype of mainly biphasic DPMs in younger patients with recurrent alterations in SETDB1 and TP53. The enrichment in biphasic histology and TILs, together with our preliminary immune checkpoint blockade response data and anecdotal clinical trial data, suggests that further evaluation of immunotherapy may be warranted in this subset.

Weakly Supervised Deep Learning Predicts Immunotherapy Response in Solid Tumors Based on PD-L1 Expression.

Programmed death-ligand 1 (PD-L1) IHC is the most commonly used biomarker for immunotherapy response. However, quantification of PD-L1 status in pathology slides is challenging. Neither manual quantification nor a computer-based mimicking of manual readouts is perfectly reproducible, and the predictive performance of both approaches regarding immunotherapy response is limited. In this study, we developed a deep learning (DL) method to predict PD-L1 status directly from raw IHC image data, without explicit intermediary steps such as cell detection or pigment quantification. We trained the weakly supervised model on PD-L1-stained slides from the non-small cell lung cancer (NSCLC)-Memorial Sloan Kettering (MSK) cohort (N = 233) and validated it on the pan-cancer-Vall d'Hebron Institute of Oncology (VHIO) cohort (N = 108). We also investigated the performance of the model to predict response to immune checkpoint inhibitors (ICI) in terms of progression-free survival. In the pan-cancer-VHIO cohort, the performance was compared with tumor proportion score (TPS) and combined positive score (CPS). The DL model showed good performance in predicting PD-L1 expression (TPS ≥ 1%) in both NSCLC-MSK and pan-cancer-VHIO cohort (AUC 0.88 ± 0.06 and 0.80 ± 0.03, respectively). The predicted PD-L1 status showed an improved association with response to ICIs [HR: 1.5 (95% confidence interval: 1-2.3), P = 0.049] compared with TPS [HR: 1.4 (0.96-2.2), P = 0.082] and CPS [HR: 1.2 (0.79-1.9), P = 0.386]. Notably, our explainability analysis showed that the model does not just look at the amount of brown pigment in the IHC slides, but also considers morphologic factors such as lymphocyte conglomerates. Overall, end-to-end weakly supervised DL shows potential for improving patient stratification for cancer immunotherapy by analyzing PD-L1 IHC, holistically integrating morphology and PD-L1 staining intensity. SIGNIFICANCE: The weakly supervised DL model to predict PD-L1 status from raw IHC data, integrating tumor staining intensity and morphology, enables enhanced patient stratification in cancer immunotherapy compared with traditional pathologist assessment.

Clinical outcomes of stereotactic body radiation therapy for malignant pleural mesothelioma.

BACKGROUND: The objective of this study is to determine the outcomes and toxicities of patients with malignant pleural mesothelioma (MPM) treated with stereotactic body radiotherapy (SBRT). MATERIALS AND METHODS: Data were extracted from an institutional tumor registry for patients diagnosed with mesothelioma and treated with SBRT. Kaplan-Meier and Cox regression analyses were employed to determine local control (LC) and overall survival (OS). RESULTS: Forty-four patients with 59 total treated tumors from December 2006 to April 2022 were identified. Fifty-one (86.4 %) cases had oligoprogressive disease (five sites or less). The median prescription dose delivered was 3000 cGy in 5 fractions (range: 2700-6000 cGy in 3-8 fractions). Fifty-one (86.4 %) tumors were in the pleura, 4 (6.8 %) spine, 2 (3.4 %) bone, 1 (1.7 %) brain, and 1 (1.7 %) pancreas. The median follow-up from SBRT completion for those alive at last follow-up was 28 months (range: 14-52 months). The most common toxicities were fatigue (50.8 %), nausea (22.0 %), pain flare (15.3 %), esophagitis (6.8 %), dermatitis (6.8 %), and pneumonitis (5.1 %). There were no grade ≥ 3 acute or late toxicities. There were 2 (3.4 %) local failures, one of the pleura and another of the spine. One-year LC was 92.9 % (95 % CI: 74.6-98.2 %) for all lesions and 96.3 % (95 % CI: 76.5-99.5 %) for pleural tumors. One-year LC was 90.9 % (95 % CI: 68.1-97.6 %) for epithelioid tumors and 92.1 % (95 % CI: 72.1-98.0 %) for oligoprogressive tumors. One-year OS from time of SBRT completion was 36.4 % (95 % CI: 22.6-50.3 %). On multivariable analysis, KPS was the lone significant predictor for OS (p = 0.029). CONCLUSIONS: Our single-institutional experience on patients with MPM suggests that SBRT is safe with a low toxicity profile and potentially achieve good local control.

Clinical and molecular features of acquired resistance to immunotherapy in non-small cell lung cancer.

Although immunotherapy with PD-(L)1 blockade is routine for lung cancer, little is known about acquired resistance. Among 1,201 patients with non-small cell lung cancer (NSCLC) treated with PD-(L)1 blockade, acquired resistance is common, occurring in >60% of initial responders. Acquired resistance shows differential expression of inflammation and interferon (IFN) signaling. Relapsed tumors can be separated by upregulated or stable expression of IFNγ response genes. Upregulation of IFNγ response genes is associated with putative routes of resistance characterized by signatures of persistent IFN signaling, immune dysfunction, and mutations in antigen presentation genes which can be recapitulated in multiple murine models of acquired resistance to PD-(L)1 blockade after in vitro IFNγ treatment. Acquired resistance to PD-(L)1 blockade in NSCLC is associated with an ongoing, but altered IFN response. The persistently inflamed, rather than excluded or deserted, tumor microenvironment of acquired resistance may inform therapeutic strategies to effectively reprogram and reverse acquired resistance.

Guidelines for Pathologic Diagnosis of Mesothelioma.

CONTEXT.­: Mesothelioma is an uncommon tumor that can be difficult to diagnose. OBJECTIVE.­: To provide updated, practical guidelines for the pathologic diagnosis of mesothelioma. DATA SOURCES.­: Pathologists involved in the International Mesothelioma Interest Group and others with expertise in mesothelioma contributed to this update. Reference material includes peer-reviewed publications and textbooks. CONCLUSIONS.­: There was consensus opinion regarding guidelines for (1) histomorphologic diagnosis of mesothelial tumors, including distinction of epithelioid, biphasic, and sarcomatoid mesothelioma; recognition of morphologic variants and patterns; and recognition of common morphologic pitfalls; (2) molecular pathogenesis of mesothelioma; (3) application of immunohistochemical markers to establish mesothelial lineage and distinguish mesothelioma from common morphologic differentials; (4) application of ancillary studies to distinguish benign from malignant mesothelial proliferations, including BAP1 and MTAP immunostains; novel immunomarkers such as Merlin and p53; fluorescence in situ hybridization (FISH) for homozygous deletion of CDKN2A; and novel molecular assays; (5) practical recommendations for routine reporting of mesothelioma, including grading epithelioid mesothelioma and other prognostic parameters; (6) diagnosis of mesothelioma in situ; (7) cytologic diagnosis of mesothelioma, including use of immunostains and molecular assays; and (8) features of nonmalignant peritoneal mesothelial lesions.

Chromothripsis-mediated small cell lung carcinoma.

Small cell lung carcinoma (SCLC) is a highly aggressive malignancy that is typically associated with tobacco exposure and inactivation of RB1 and TP53 genes. Here we performed detailed clinicopathologic, genomic and transcriptomic profiling of an atypical subset of SCLC that lacked RB1 and TP53 co-inactivation and arose in never/light smokers. We found that most cases were associated with chromothripsis - massive, localized chromosome shattering - recurrently involving chromosomes 11 or 12, and resulting in extrachromosomal (ecDNA) amplification of CCND1 or co-amplification of CCND2/CDK4/MDM2, respectively. Uniquely, these clinically aggressive tumors exhibited genomic and pathologic links to pulmonary carcinoids, suggesting a previously uncharacterized mode of SCLC pathogenesis via transformation from lower-grade neuroendocrine tumors or their progenitors. Conversely, SCLC in never-smokers harboring inactivated RB1 and TP53 exhibited hallmarks of adenocarcinoma-to-SCLC derivation, supporting two distinct pathways of plasticity-mediated pathogenesis of SCLC in never-smokers.

Diagnosis of thoracic SMARCA4-deficient undifferentiated tumor in cytology.

INTRODUCTION: Although alterations in SMARCA4-deficient occur in non-small cell lung carcinoma (SD-NSCLC), thoracic SMARCA4-deficient undifferentiated tumor (TSDUT) is recognized as a distinct entity in the 2021 World Health Organization Classification of Thoracic Tumors because of unique morphologic, immunophenotypic and molecular features, and worse survival compared with SD-NSCLC. Cytologic diagnosis of TSDUT is clinically important because of its aggressive behavior and because it is often diagnosed by fine-needle aspiration because TSDUTs are usually unresectable at presentation. Here, we identify cytologic features that can be used for recognition of TSDUT and distinction from SD-NSCLC. MATERIALS AND METHODS: Cytomorphologic features were investigated in cytology specimens from patients with TSDUT (n = 11) and compared with a control group of patients with SD-NSCLC (n = 20). RESULTS: The presence of classic rhabdoid morphology, at least focally, was entirely specific for TSDUT (n = 6, 55%) compared with SD-NSCLC (n = 0) in this study. TSDUT more frequently showed tumor necrosis (n = 11, 100% vs. n = 8, 40%; p = .001), dominant single-cell pattern on aspirate smears or touch preparation slides (n = 8 [of 9], 80% vs. n = 3, 15%; p = .010), nuclear molding (n = 5, 45% vs. n = 1, 5%; p = .013), and indistinct cell borders (n = 11, 100% vs. n = 5, 25%; P < .001) compared with SD-NSCLC, respectively. CONCLUSIONS: Cytomorphologic features occurring more frequently in TSDUT include tumor necrosis, dominant single-cell pattern, nuclear molding indistinct cell borders, and focal rhabdoid cells. Presence of these features in a cytology specimen of an undifferentiated tumor, particularly in a patient with a thoracic mass, should raise suspicion for TSDUT and prompt appropriate ancillary workup.