Subba R. Digumarthy

Isolation of rare circulating tumour cells in cancer patients by microchip technology

Viable tumour-derived epithelial cells (circulating tumour cells or CTCs) have been identified in peripheral blood from cancer patients and are probably the origin of intractable metastatic disease. Although extremely rare, CTCs represent a potential alternative to invasive biopsies as a source of tumour tissue for the detection, characterization and monitoring of non-haematologic cancers. The ability to identify, isolate, propagate and molecularly characterize CTC subpopulations could further the discovery of cancer stem cell biomarkers and expand the understanding of the biology of metastasis. Current strategies for isolating CTCs are limited to complex analytic approaches that generate very low yield and purity. Here we describe the development of a unique microfluidic platform (the ‘CTC-chip’) capable of efficient and selective separation of viable CTCs from peripheral whole blood samples, mediated by the interaction of target CTCs with antibody (EpCAM)-coated microposts under precisely controlled laminar flow conditions, and without requisite pre-labelling or processing of samples. The CTC-chip successfully identified CTCs in the peripheral blood of patients with metastatic lung, prostate, pancreatic, breast and colon cancer in 115 of 116 (99%) samples, with a range of 5–1,281 CTCs per ml and approximately 50% purity. In addition, CTCs were isolated in 7/7 patients with early-stage prostate cancer. Given the high sensitivity and specificity of the CTC-chip, we tested its potential utility in monitoring response to anti-cancer therapy. In a small cohort of patients with metastatic cancer undergoing systemic treatment, temporal changes in CTC numbers correlated reasonably well with the clinical course of disease as measured by standard radiographic methods. Thus, the CTC-chip provides a new and effective tool for accurate identification and measurement of CTCs in patients with cancer. It has broad implications in advancing both cancer biology research and clinical cancer management, including the detection, diagnosis and monitoring of cancer.

Genotypic and Histological Evolution of Lung Cancers Acquiring Resistance to EGFR Inhibitors

Lung cancers undergo dynamic genetic and histological changes upon developing resistance to EGFR inhibitors. The Shifting Sands of Lung Cancer Lung cancer is the leading cause of death globally and has proven very difficult to treat. The development almost a decade ago of tyrosine kinase inhibitors that specifically block the epidermal growth factor receptor (EGFR), which is switched on in many lung cancers, provided hope that targeted therapies would finally combat this deadly disease. However, only a certain subpopulation of lung cancer patients carrying specific activating mutations in EGFR responded clinically to EGFR inhibitors, and even among these patients, resistance to the inhibitor emerged within 12 months. To better understand how lung cancers develop drug resistance, Sequist and colleagues undertook a comprehensive genetic and histological analysis of 37 patients with non–small cell lung cancer (NSCLC), and they made some surprising discoveries. In an effort to understand the exact mechanism underscoring the acquisition of drug resistance in NSCLC patients treated with EGFR inhibitors, the investigators analyzed tumor biopsies from patients at the time they acquired resistance. All of the lung cancer patients retained their original activating EGFR mutations, but some patients had acquired another mutation in EGFR (T790M), which interferes with binding of the drug to the receptor, rendering the tumors resistant. Meanwhile, another group of patients became resistant because they developed amplification of a gene encoding the MET tyrosine kinase receptor, which, like EGFR, drives cell growth. Yet other patients acquired drug resistance mechanisms that had not been reported before including amplification of the EGFR gene itself and mutations in the PIK3CA gene (which encodes a subunit of the signaling molecule phosphatidylinositol 3-kinase). In addition, the authors observed that a few lung cancers transitioned from an epithelial cell morphology to a mesenchymal cell–like appearance, which is associated with a more aggressive type of tumor. In five patients, the authors discovered another type of transition that was even more surprising: the conversion of NSCLCs into small cell lung cancers (SCLCs), which are easier to treat. Indeed, these five patients responded well to the typical chemotherapy regimen used to treat SCLCs. To study the evolution of lung tumors in patients over the course of their disease, the investigators took serial biopsies from three lung cancer patients over 2 years. They found that when the patients acquired drug resistance and were then taken off the EGFR inhibitor, they lost the resistance mutations and their tumors once again became sensitive to treatment by either the same or a different EGFR inhibitor. The detailed genetic and histological analysis by Sequist and colleagues provides new insights into the shifting sands of drug resistance evolution in lung cancers and suggests that serial biopsies may be essential in the quest to reverse or even prevent the development of drug resistance. Lung cancers harboring mutations in the epidermal growth factor receptor (EGFR) respond to EGFR tyrosine kinase inhibitors, but drug resistance invariably emerges. To elucidate mechanisms of acquired drug resistance, we performed systematic genetic and histological analyses of tumor biopsies from 37 patients with drug-resistant non–small cell lung cancers (NSCLCs) carrying EGFR mutations. All drug-resistant tumors retained their original activating EGFR mutations, and some acquired known mechanisms of resistance including the EGFR T790M mutation or MET gene amplification. Some resistant cancers showed unexpected genetic changes including EGFR amplification and mutations in the PIK3CA gene, whereas others underwent a pronounced epithelial-to-mesenchymal transition. Surprisingly, five resistant tumors (14%) transformed from NSCLC into small cell lung cancer (SCLC) and were sensitive to standard SCLC treatments. In three patients, serial biopsies revealed that genetic mechanisms of resistance were lost in the absence of the continued selective pressure of EGFR inhibitor treatment, and such cancers were sensitive to a second round of treatment with EGFR inhibitors. Collectively, these results deepen our understanding of resistance to EGFR inhibitors and underscore the importance of repeatedly assessing cancers throughout the course of the disease.

Clinical Features and Outcome of Patients With Non–Small-Cell Lung Cancer Who Harbor EML4-ALK

PURPOSE The EML4-ALK fusion oncogene represents a novel molecular target in a small subset of non-small-cell lung cancers (NSCLC). To aid in identification and treatment of these patients, we examined the clinical characteristics and treatment outcomes of patients who had NSCLC with and without EML4-ALK. PATIENTS AND METHODS Patients with NSCLC were selected for genetic screening on the basis of two or more of the following characteristics: female sex, Asian ethnicity, never/light smoking history, and adenocarcinoma histology. EML4-ALK was identified by using fluorescent in situ hybridization for ALK rearrangements and was confirmed by immunohistochemistry for ALK expression. EGFR and KRAS mutations were determined by DNA sequencing. RESULTS Of 141 tumors screened, 19 (13%) were EML4-ALK mutant, 31 (22%) were EGFR mutant, and 91 (65%) were wild type (WT/WT) for both ALK and EGFR. Compared with the EGFR mutant and WT/WT cohorts, patients with EML4-ALK mutant tumors were significantly younger (P < .001 and P = .005) and were more likely to be men (P = .036 and P = .039). Patients with EML4-ALK-positive tumors, like patients who harbored EGFR mutations, also were more likely to be never/light smokers compared with patients in the WT/WT cohort (P < .001). Eighteen of the 19 EML4-ALK tumors were adenocarcinomas, predominantly the signet ring cell subtype. Among patients with metastatic disease, EML4-ALK positivity was associated with resistance to EGFR tyrosine kinase inhibitors (TKIs). Patients in the EML4-ALK cohort and the WT/WT cohort showed similar response rates to platinum-based combination chemotherapy and no difference in overall survival. CONCLUSION EML4-ALK defines a molecular subset of NSCLC with distinct clinical characteristics. Patients who harbor this mutation do not benefit from EGFR TKIs and should be directed to trials of ALK-targeted agents.

Detection of Mutations in EGFR in Circulating Lung-Cancer Cells

BACKGROUND The use of tyrosine kinase inhibitors to target the epidermal growth factor receptor gene (EGFR) in patients with non-small-cell lung cancer is effective but limited by the emergence of drug-resistance mutations. Molecular characterization of circulating tumor cells may provide a strategy for noninvasive serial monitoring of tumor genotypes during treatment. METHODS We captured highly purified circulating tumor cells from the blood of patients with non-small-cell lung cancer using a microfluidic device containing microposts coated with antibodies against epithelial cells. We performed EGFR mutational analysis on DNA recovered from circulating tumor cells using allele-specific polymerase-chain-reaction amplification and compared the results with those from concurrently isolated free plasma DNA and from the original tumor-biopsy specimens. RESULTS We isolated circulating tumor cells from 27 patients with metastatic non-small-cell lung cancer (median number, 74 cells per milliliter). We identified the expected EGFR activating mutation in circulating tumor cells from 11 of 12 patients (92%) and in matched free plasma DNA from 4 of 12 patients (33%) (P=0.009). We detected the T790M mutation, which confers drug resistance, in circulating tumor cells collected from patients with EGFR mutations who had received tyrosine kinase inhibitors. When T790M was detectable in pretreatment tumor-biopsy specimens, the presence of the mutation correlated with reduced progression-free survival (7.7 months vs. 16.5 months, P<0.001). Serial analysis of circulating tumor cells showed that a reduction in the number of captured cells was associated with a radiographic tumor response; an increase in the number of cells was associated with tumor progression, with the emergence of additional EGFR mutations in some cases. CONCLUSIONS Molecular analysis of circulating tumor cells from the blood of patients with lung cancer offers the possibility of monitoring changes in epithelial tumor genotypes during the course of treatment.

Implementing multiplexed genotyping of non-small-cell lung cancers into routine clinical practice

BACKGROUND Personalizing non-small-cell lung cancer (NSCLC) therapy toward oncogene addicted pathway inhibition is effective. Hence, the ability to determine a more comprehensive genotype for each case is becoming essential to optimal cancer care. METHODS We developed a multiplexed PCR-based assay (SNaPshot) to simultaneously identify >50 mutations in several key NSCLC genes. SNaPshot and FISH for ALK translocations were integrated into routine practice as Clinical Laboratory Improvement Amendments-certified tests. Here, we present analyses of the first 589 patients referred for genotyping. RESULTS Pathologic prescreening identified 552 (95%) tumors with sufficient tissue for SNaPshot; 51% had ≥1 mutation identified, most commonly in KRAS (24%), EGFR (13%), PIK3CA (4%) and translocations involving ALK (5%). Unanticipated mutations were observed at lower frequencies in IDH and β-catenin. We observed several associations between genotypes and clinical characteristics, including increased PIK3CA mutations in squamous cell cancers. Genotyping distinguished multiple primary cancers from metastatic disease and steered 78 (22%) of the 353 patients with advanced disease toward a genotype-directed targeted therapy. CONCLUSIONS Broad genotyping can be efficiently incorporated into an NSCLC clinic and has great utility in influencing treatment decisions and directing patients toward relevant clinical trials. As more targeted therapies are developed, such multiplexed molecular testing will become a standard part of practice.

Adaptive Statistical Iterative Reconstruction Technique for Radiation Dose Reduction in Chest CT: A Pilot Study

PURPOSE To compare lesion detection and image quality of chest computed tomographic (CT) images acquired at various tube current-time products (40-150 mAs) and reconstructed with adaptive statistical iterative reconstruction (ASIR) or filtered back projection (FBP). MATERIALS AND METHODS In this Institutional Review Board-approved HIPAA-compliant study, CT data from 23 patients (mean age, 63 years ± 7.3 [standard deviation]; 10 men, 13 women) were acquired at varying tube current-time products (40, 75, 110, and 150 mAs) on a 64-row multidetector CT scanner with 10-cm scan length. All patients gave informed consent. Data sets were reconstructed at 30%, 50%, and 70% ASIR-FBP blending. Two thoracic radiologists assessed image noise, visibility of small structures, lesion conspicuity, and diagnostic confidence. Objective noise and CT number were measured in the thoracic aorta. CT dose index volume, dose-length product, weight, and transverse diameter were recorded. Data were analyzed by using analysis of variance and the Wilcoxon signed rank test. RESULTS FBP had unacceptable noise at 40 and 75 mAs in 17 and five patients, respectively, whereas ASIR had acceptable noise at 40-150 mAs. Objective noise with 30%, 50%, and 70% ASIR blending (11.8 ± 3.8, 9.6 ± 3.1, and 7.5 ± 2.6, respectively) was lower than that with FBP (15.8 ± 4.8) (P < .0001). No lesions were missed on FBP or ASIR images. Lesion conspicuity was graded as well seen on both FBP and ASIR images (P < .05). Mild pixilated blotchy texture was noticed with 70% blended ASIR images. CONCLUSION Acceptable image quality can be obtained for chest CT images acquired at 40 mAs by using ASIR without any substantial artifacts affecting diagnostic confidence. SUPPLEMENTAL MATERIAL http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.11101450/-/DC1.

Acquired Resistance to Crizotinib from a Mutation in CD74–ROS1

Crizotinib, an inhibitor of anaplastic lymphoma kinase (ALK), has also recently shown efficacy in the treatment of lung cancers with ROS1 translocations. Resistance to crizotinib developed in a patient with metastatic lung adenocarcinoma harboring a CD74-ROS1 rearrangement who had initially shown a dramatic response to treatment. We performed a biopsy of a resistant tumor and identified an acquired mutation leading to a glycine-to-arginine substitution at codon 2032 in the ROS1 kinase domain. Although this mutation does not lie at the gatekeeper residue, it confers resistance to ROS1 kinase inhibition through steric interference with drug binding. The same resistance mutation was observed at all the metastatic sites that were examined at autopsy, suggesting that this mutation was an early event in the clonal evolution of resistance. (Funded by Pfizer and others; ClinicalTrials.gov number, NCT00585195.).

BIM expression in treatment-naïve cancers predicts responsiveness to kinase inhibitors

Cancers with specific genetic mutations are susceptible to selective kinase inhibitors. However, there is a wide spectrum of benefit among cancers harboring the same sensitizing genetic mutations. Herein, we measured apoptotic rates among cell lines sharing the same driver oncogene following treatment with the corresponding kinase inhibitor. There was a wide range of kinase inhibitor-induced apoptosis despite comparable inhibition of the target and associated downstream signaling pathways. Surprisingly, pretreatment RNA levels of the BH3-only pro-apoptotic BIM strongly predicted the capacity of EGFR, HER2, and PI3K inhibitors to induce apoptosis in EGFR-mutant, HER2-amplified, and PIK3CA-mutant cancers, respectively, but BIM levels did not predict responsiveness to standard chemotherapies. Furthermore, BIM RNA levels in EGFR-mutant lung cancer specimens predicted response and duration of clinical benefit from EGFR inhibitors. These findings suggest assessment of BIM levels in treatment-naïve tumor biopsies may indicate the degree of benefit from single-agent kinase inhibitors in multiple oncogene-addiction paradigms.

Heterogeneity Underlies the Emergence of EGFRT790 Wild-Type Clones Following Treatment of T790M-Positive Cancers with a Third-Generation EGFR Inhibitor

UNLABELLED Rociletinib is a third-generation EGFR inhibitor active in lung cancers with T790M, the gatekeeper mutation underlying most first-generation EGFR drug resistance. We biopsied patients at rociletinib progression to explore resistance mechanisms. Among 12 patients with T790M-positive cancers at rociletinib initiation, six had T790-wild-type rociletinib-resistant biopsies. Two T790-wild-type cancers underwent small cell lung cancer transformation; three T790M-positive cancers acquired EGFR amplification. We documented T790-wild-type and T790M-positive clones coexisting within a single pre-rociletinib biopsy. The pretreatment fraction of T790M-positive cells affected response to rociletinib. Longitudinal circulating tumor DNA (ctDNA) analysis revealed an increase in plasma EGFR-activating mutation, and T790M heralded rociletinib resistance in some patients, whereas in others the activating mutation increased but T790M remained suppressed. Together, these findings demonstrate the role of tumor heterogeneity when therapies targeting a singular resistance mechanism are used. To further improve outcomes, combination regimens that also target T790-wild-type clones are required. SIGNIFICANCE This report documents that half of T790M-positive EGFR-mutant lung cancers treated with rociletinib are T790-wild-type upon progression, suggesting that T790-wild-type clones can emerge as the dominant source of resistance. We show that tumor heterogeneity has important clinical implications and that plasma ctDNA analyses can sometimes predict emerging resistance mechanisms.

EGFR Mutations and ALK Rearrangements Are Associated with Low Response Rates to PD-1 Pathway Blockade in Non–Small Cell Lung Cancer: A Retrospective Analysis

Purpose: PD-1 inhibitors are established agents in the management of non–small cell lung cancer (NSCLC); however, only a subset of patients derives clinical benefit. To determine the activity of PD-1/PD-L1 inhibitors within clinically relevant molecular subgroups, we retrospectively evaluated response patterns among EGFR-mutant, anaplastic lymphoma kinase (ALK)-positive, and EGFR wild-type/ALK-negative patients. Experimental Design: We identified 58 patients treated with PD-1/PD-L1 inhibitors. Objective response rates (ORR) were assessed using RECIST v1.1. PD-L1 expression and CD8+ tumor-infiltrating lymphocytes (TIL) were evaluated by IHC. Results: Objective responses were observed in 1 of 28 (3.6%) EGFR-mutant or ALK-positive patients versus 7 of 30 (23.3%) EGFR wild-type and ALK-negative/unknown patients (P = 0.053). The ORR among never- or light- (≤10 pack years) smokers was 4.2% versus 20.6% among heavy smokers (P = 0.123). In an independent cohort of advanced EGFR-mutant (N = 68) and ALK-positive (N = 27) patients, PD-L1 expression was observed in 24%/16%/11% and 63%/47%/26% of pre–tyrosine kinase inhibitor (TKI) biopsies using cutoffs of ≥1%, ≥5%, and ≥50% tumor cell staining, respectively. Among EGFR-mutant patients with paired, pre- and post-TKI–resistant biopsies (N = 57), PD-L1 expression levels changed after resistance in 16 (28%) patients. Concurrent PD-L1 expression (≥5%) and high levels of CD8+ TILs (grade ≥2) were observed in only 1 pretreatment (2.1%) and 5 resistant (11.6%) EGFR-mutant specimens and was not observed in any ALK-positive, pre- or post-TKI specimens. Conclusions: NSCLCs harboring EGFR mutations or ALK rearrangements are associated with low ORRs to PD-1/PD-L1 inhibitors. Low rates of concurrent PD-L1 expression and CD8+ TILs within the tumor microenvironment may underlie these clinical observations. Clin Cancer Res; 22(18); 4585–93. ©2016 AACR. See related commentary by Gettinger and Politi, p. 4539