Faculty Bibliography

Immune checkpoint inhibitors, which unleash a patient's own T cells to kill tumors, are revolutionizing cancer treatment. To unravel the genomic determinants of response to this therapy, we used whole-exome sequencing of non-small cell lung cancers treated with pembrolizumab, an antibody targeting programmed cell death-1 (PD-1). In two independent cohorts, higher nonsynonymous mutation burden in tumors was associated with improved objective response, durable clinical benefit, and progression-free survival. Efficacy also correlated with the molecular smoking signature, higher neoantigen burden, and DNA repair pathway mutations; each factor was also associated with mutation burden. In one responder, neoantigen-specific CD8+ T cell responses paralleled tumor regression, suggesting that anti-PD-1 therapy enhances neoantigen-specific T cell reactivity. Our results suggest that the genomic landscape of lung cancers shapes response to anti-PD-1 therapy.

Core biopsies obtained using PET/CT guidance contain bound radiotracer and therefore provide information about tracer uptake in situ. Our goal is to develop a method for Quantitative Autoradiography of Biopsy Specimens (QABS), to use this method to correlate 18F-fluorodeoxyglucose (FDG) tracer uptake in situ with histopathology findings, and to briefly discuss its potential application. METHODS: Twenty seven (27) patients referred for a PET/CT-guided biopsy of FDG-avid primary or metastatic lesions in different locations consented to participate in this institutional review board-approved, HIPAA compliant study. Autoradiography (ARG) of biopsy specimens obtained using five types of needles was performed immediately after extraction. The response of ARG imaging plates was calibrated using dummy specimens with known activity obtained using two core biopsy needle sizes. The calibration curves were used to quantify the activity along biopsy specimens obtained with these two needles and to calculate standardized uptake values, SUVARG. ARG images were correlated with histopathologic findings and fused with PET/CT images demonstrating the position of the biopsy needle within the lesion. Logistic regression analysis was performed to search for SUVARG threshold distinguishing benign from malignant tissue in liver biopsy specimens. Pearson correlation between SUVARG of the whole biopsy specimen and average SUVPET over the voxels intersected by the needle in the fused PET/CT was calculated. RESULTS: Activity concentrations were obtained using ARG for 20 specimens extracted with 18G and 20G needles. The probability for finding malignancy in a specimen is larger than 50% (95 % confidence) if SUVARG is larger than 7.3. For core specimens with preserved shape and orientation and in the absence of motion, ARG, CT and PET images registration with spatial accuracy better than 2 mm is achievable. The correlation coefficient between specimen mean SUVARG and SUVPET was 0.66. CONCLUSION: Performing QABS on core biopsy specimens obtained using PET/CT guidance enables in situ correlation of FDG tracer uptake and histopathology on a millimeter scale. QABS promises to provide useful information for guiding interventional radiology procedures and localized therapies and for in situ high spatial resolution validation of radiopharmaceuticals uptake.

BACKGROUND: The characterization of the molecular alterations in thymic epithelial tumors may lead to a better understanding of tumorigenesis, new therapeutic targets, and biomarkers in these tumors. METHODS: Paired tissue (tumor and matched normal) from 15 thymic carcinomas (TCA) and six B3 thymomas were evaluated by exon capture of 275 cancer-related genes, followed by deep coverage next-generation sequencing, which identifies somatic sequence variants, small insertions and deletions, and copy number alterations involving all exons of the captured genes. RESULTS: Non-silent somatic mutations were identified in 12 of 15 (80%) TCA with a median of one mutation per tumor (range 0-26). Recurrent mutations were identified in tumor suppressor genes TP53 (n = 4), SMAD4 (n = 2), and CYLD (n = 2); and chromatin remodeling genes KDM6A (n = 3), SETD2 (n = 2), MLL3 (n = 2), and MLL2 (n = 2). Tumors with TP53 mutation appeared to exhibit more aggressive behavior. Therefore, the role of P53 was evaluated by immunohistochemistry in an additional ten cases. P53 overexpression correlated with TP53 mutation. These tumors had a higher rate of recurrence and death of disease compared to carcinoma with normal p53 expression (p = 0.02 for disease-free survival and p = 0.05 for overall survival). Among the B3 thymomas, mutations were identified in four of six tumors. Mutations in BCOR (BCL6 co-repressor) were seen in three thymomas and MLL3 (involved in histone methylation) in one tumor. CONCLUSIONS: Next-generation sequencing of cancer genes in thymic epithelial tumors revealed a low frequency of mutation, with different patterns between TCA and B3 thymomas. TP53 and BCOR were the most frequently mutated genes in TCA and B3 thymomas, respectively. Alterations in p53 are associated with worse prognosis in TCA.

BACKGROUND: Thymic carcinomas are rare cancers with limited data regarding outcomes, particularly for those patients with advanced disease. METHODS: We identified patients with thymic carcinomas diagnosed between 1993 and 2012. Patient characteristics, recurrence-free survival (RFS), and overall survival (OS) were analyzed. RESULTS: One hundred twenty-one patients with thymic carcinomas were identified. Higher Masaoka stage was associated with worse OS and RFS (5-year OS of 100%, 81%, 51%, 24%, and 17% for stage I, II, III, IVa, and IVb respectively, p < 0.001 and 5-year RFS of 80%, 28%, and 7% for stage I/II, III, and IV respectively, p < 0.001). Patients with stage IVb lymph node (LN) only disease had a better 5-year OS as compared with patients with distant metastasis (24% versus 7%, p = 0.025). Of the 61 patients with stage IVb disease, 22 of 29 patients (76%) with LN-only disease underwent curative intent resection versus 3 of 32 patients (9%) with distant metastasis. Twenty-two patients with LN involvement were treated with multimodality therapy. Three (14%) remain free of disease with long-term follow-up (range, 3.4+ years- to 6.8+ years). CONCLUSIONS: We describe the clinical features of a large series of patients with thymic carcinoma in North America. The Masaoka staging system effectively prognosticated OS and RFS. Patients with stage IVb LN-only disease had significantly better OS as compared with patients with distant metastasis with a subset of patients sustaining long-term RFS with multimodality therapy. If validated, these data would support a revised staging system with subclassification of stage IVb disease into two groups.

The past decade has seen an enormous advancement in the therapy for lung cancer, predominantly seen in adenocarcinoma, ranging from the introduction of histology-based drugs to the discovery of targetable mutations. These events have led to a personalized therapeutic approach with the delivery of drugs that target specific oncogenic pathways active in a given tumor with the intent of acquiring the best response rate. The discovery of sensitizing mutation in the epidermal growth factor receptor gene as the basis for clinical response to tyrosine kinase inhibitors led to a systematic search for other molecular targets in lung cancer. Currently, there are several molecular alterations that can be targeted by experimental drugs. These new discoveries would not be possible without a parallel technological evolution in diagnostic molecular pathology. Next-generation sequencing (NGS) is a technology that allows for the evaluation of multiple molecular alterations in the same sample using a small amount of tissue. Selective evaluation of targeted cancer genes, instead of whole-genome evaluation, is the approach that is best suited to enter clinical practice. This technology allows for the detection of most molecular alteration with a single test, thus saving tissue for future discoveries. The use of NGS is expected to increase and gain importance in clinical and experimental approaches, since it can be used as a diagnostic tool as well as for new discoveries. The technique may also help us elucidate the interplay of several genes and their alteration in the mechanism of drug response and resistance.

INTRODUCTION: The 2004 World Health Organization classification of lung cancer contained three major forms of non-small-cell lung cancer: squamous cell carcinoma (SqCC), adenocarcinoma (AdC), and large cell carcinoma. The goal of this study was first, to assess the reproducibility of a set of histopathological features for SqCC in relation to other poorly differentiated non-small-cell lung cancers and second, to assess the value of immunohistochemistry in improving the diagnosis. METHODS: Resection specimens (n = 37) with SqCC, large cell carcinoma, basaloid carcinoma, sarcomatoid carcinoma, lymphoepithelial-like carcinoma, and solid AdC, were contributed by the participating pathologists. Hematoxylin and eosin (H&E) stained slides were digitized. The diagnoses were evaluated in two ways. First, the histological criteria were evaluated and the (differential) diagnosis on H&E alone was scored. Second, the added value of additional stains to make an integrated diagnosis was examined. RESULTS: The histologic criteria defining SqCC were consistently used, but in poorly differentiated cases they were infrequently present, rendering the diagnosis more difficult. Kappa scores on H&E alone were for SqCC 0.46, large cell carcinoma 0.25, basaloid carcinoma 0.27, sarcomatoid carcinoma 0.52, lymphoepithelial-like carcinoma 0.56, and solid AdC 0.21. The kappa score improved with the use of additional stains for SqCC (combined with basaloid carcinoma) to 0.57, for solid AdC to 0.63. CONCLUSION: The histologic criteria that may be used in the differential diagnosis of poorly differentiated lung cancer were more precisely refined. Furthermore, additional stains improved the reproducibility of histological diagnosis of SqCC and AdC, uncovering information that was not present in routine H&E stained slides.

Multiple reports indicate that epidermal growth factor receptor (EGFR) mutations are associated with lepidic-pattern lung adenocarcinoma and that KRAS mutations are associated with invasive mucinous adenocarcinoma. We sought to investigate the association between EGFR and KRAS mutations and specific morphologic characteristics, such as predominant histologic subtype and mucinous features. Clinical data for 864 patients with resected lung adenocarcinoma that underwent molecular testing for EGFR and KRAS mutations were collected. Histologic subtyping was performed according to the IASLC/ATS/ERS lung adenocarcinoma classification, with attention given to signet-ring cell feature and extracellular mucin. EGFR mutations were detected using a polymerase chain reaction-based sizing assay, KRAS mutations were detected using Sanger sequencing, and ALK expression was detected using immunohistochemistry. Invasive mucinous adenocarcinoma was associated with KRAS mutation (P<0.001). Among invasive mucinous adenocarcinomas with KRAS mutation, a pure mucinous pattern was more common than a mixed mucinous/nonmucinous pattern (P=0.002). Invasive mucinous adenocarcinoma was associated with KRAS transition mutations (G-->A) but not transversion mutations (G-->T or G-->C) compared with nonmucinous tumors (P=0.009). The lepidic-predominant group was associated with EGFR mutation compared with nonlepidic-predominant tumors (P=0.011). Extracellular mucin was associated with KRAS mutation (P<0.001), whereas signet-ring cell feature was not associated with EGFR or KRAS mutation (P=0.517). ALK expression was associated with signet-ring cell feature (P=0.001) but not with extracellular mucin (P=0.089). Our study shows that histologic patterns of mucin in lung adenocarcinoma-including invasive mucinous adenocarcinoma and extracellular mucin-are associated with KRAS mutation.

Context.-Thymic epithelial tumors are rare, constituting interpretive challenges for pathologists. Digital imaging can be useful as an educational tool for these rare tumors. Objectives.-To evaluate the diagnostic reproducibility of thymic tumors among thoracic pathologists. Design.-Twenty cases of thymoma or thymic carcinoma were scanned into the Aperio system. The images were sent to pathologists with expertise in thoracic pathology at 6 different centers, who were asked to classify the tumors according to the 2004 World Heath Organization classification and to diagnose invasion. Interobserver agreement was evaluated. After discussion of the first 20 cases, a second set of 10 cases was evaluated. Results.-There was agreement for the diagnosis of thymoma and thymic carcinoma in 70% of cases (n = 14); in the remaining 6 cases, there was disagreement for cases of B3 thymoma (n = 5) and type A thymoma (n = 1) and thymic carcinoma. The overall kappa was 0.39. When invasion was evaluated, the overall kappa was 0.45. In the second round of the study, after discussion of diagnostic criteria, the interobserver agreement for the diagnosis of thymoma versus thymic carcinoma was 0.67 and that for the determination of invasion was 0.57-suggesting interpretative improvement. Conclusion.-The reproducibility of diagnosis of thymic epithelial tumors, using digital imaging, is comparable to that in previous studies using glass slides. Digital imaging is a good tool for remote consultation and for educational purposes. This technology could be used to train pathologists with low-level experience in thymic epithelial tumors and to foster collaborative work in the field.

The 2011 International Association for the Study of Lung Cancer (IASLC)/American Thoracic Society (ATS)/European Respiratory Society (ERS) lung adenocarcinoma classification emphasizes the prognostic significance of histologic subtypes. However, one limitation of this classification is that the highest percentage of patients ( approximately 40%) is classified as acinar predominant tumors, and these patients display a spectrum of favorable and unfavorable clinical behaviors. We investigated whether the cribriform pattern can further stratify prognosis by histologic subtype. Tumor slides from 1038 patients with stage I lung adenocarcinoma (1995-2009) were reviewed. Tumors were classified according to the IASLC/ATS/ERS classification. The percentage of cribriform pattern was recorded, and the cribriform predominant subtype was considered as a subtype for analysis. The log-rank test was used to analyze the association between histologic variables and recurrence-free probability. The 5-year recurrence-free probability for patients with cribriform predominant tumors (n=46) was 70%. The recurrence-free probability for patients with cribriform predominant tumors was significantly lower than that for patients with acinar (5-year recurrence-free probability, 87%; P=0.002) or papillary predominant tumors (83%; P=0.020) but was comparable to that for patients with micropapillary (P=0.34) or solid predominant tumors (P=0.56). The recurrence-free probability for patients with >/=10% cribriform pattern tumors (n=214) was significantly lower (5-year recurrence-free probability, 73%) than that for patients with <10% cribriform pattern tumors (n=824; 84%; P<0.001). In multivariate analysis, patients with acinar predominant tumors with >/=10% cribriform pattern remained at significantly increased risk of recurrence compared with those with <10% cribriform pattern (P=0.042). Cribriform predominant tumors should be considered a distinct subtype with a high risk of recurrence, and presence (>/=10%) of the cribriform pattern is an independent predictor of recurrence, identifying a poor prognostic subset of acinar predominant tumors. Our findings highlight the important prognostic value of comprehensive histologic subtyping and recording the percentage of each histologic pattern, according to the IASLC/ATS/ERS classification with the addition of the cribriform subtype.

Tunneling nanotubes (TnTs) are long, non-adherent, actin-based cellular extensions that act as conduits for transport of cellular cargo between connected cells. The mechanisms of nanotube formation and the effects of the tumor microenvironment and cellular signals on TnT formation are unknown. In the present study, we explored exosomes as potential mediators of TnT formation in mesothelioma and the potential relationship of lipid rafts to TnT formation. Mesothelioma cells co-cultured with exogenous mesothelioma-derived exosomes formed more TnTs than cells cultured without exosomes within 24-48 h; and this effect was most prominent in media conditions (low-serum, hyperglycemic medium) that support TnT formation (1.3-1.9-fold difference). Fluorescence and electron microscopy confirmed the purity of isolated exosomes and revealed that they localized predominantly at the base of and within TnTs, in addition to the extracellular environment. Time-lapse microscopic imaging demonstrated uptake of tumor exosomes by TnTs, which facilitated intercellular transfer of these exosomes between connected cells. Mesothelioma cells connected via TnTs were also significantly enriched for lipid rafts at nearly a 2-fold higher number compared with cells not connected by TnTs. Our findings provide supportive evidence of exosomes as potential chemotactic stimuli for TnT formation, and also lipid raft formation as a potential biomarker for TnT-forming cells.