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MINI 23 - Lung Cancer Risk: Genetic Susceptibility and Airway Biology (ID 135)
- Event: WCLC 2015
- Type: Mini Oral
- Track: Screening and Early Detection
- Presentations: 1
MINI23.10 - Subtraction of Allelic Fractions (Delta-θ): A Sensitive Metric to Detect Chromosomal Alterations in Heterogeneous Premalignant Specimens (ID 2434)
16:45 - 18:15 | Author(s): K. Soejima
Lung squamous carcinoma is believed to arise from premalignant bronchial epithelial dysplasia, which demonstrates progressive histologic changes leading up to invasive cancer. However, only a small subset of these lesions progress to carcinoma. Recent studies have shown that somatic chromosomal alterations (SCAs) status is a better biomarker than premalignant histology alone. Single-nucleotide polymorphism microarray (SNP array) has been frequently used to delineate these genomic alterations across the whole genome. However, the cellular heterogeneity, from clinical samples such as endobronchial specimens, is a basic obstacle to perform sensitive and accurate detection of SCAs.
We used: 1) a lung cancer cell line (NCI-H1395) and its matched lymphoblastoid (NCI-BL1395) cell line; 2) frozen lung tissues containing different percentage of invasive cancer cells surgically resected from a patient; and 3) biopsies and brushings obtained at the visually concerning areas during bronchoscopy. The histology of the clinical samples were graded by the study pathologist. Genomic DNA was isolated from each sample, quantified, and labeled for Illumina SNP array (HumanOmni 2.5-Quad BeadChip). Data analysis and visualizations were performed using Partek Genomic Suite 6.6 software.
Our study focused on the detection of SCAs by the comparison of genomic DNAs from cancer/premalignant cells (subject) to blood/normal cells (reference) from the same individual. We tested a B allele frequency metric, the subtraction of allelic fractions (delta-θ), on a standardized mixture of genomic DNAs from a lung cancer cell line and its matched lymphoblastoid cell line. Delta-θ proved to be a sensitive parameter to clearly delineate SCAs present in the tumor cell line even with a large proportion of normal cells (up to 90%). To explore the utility of using delta-θ for heterogeneous samples, we used clinical lung cancer specimens with known cancer cell content. In comparison to the other publicly available analytical metrics/algorithms (conventional Log R Ratio plot, mirrored B Allele Frequency plot, and GAP algorithm), delta-θ performed as well or better (with lower computational power needed), and enabled the detection of SCAs even in highly heterogeneous clinical samples (<30% tumor cell content). In addition, we completed a study using a number of bronchial biopsies and brushings with histologic grade ranging from normal to squamous cell carcinoma. SCAs were rarely detected in those of low to mild dysplasia, while they were detected in approximately 25% of moderate or severe dysplasia, and in all carcinoma in situ (CIS) and squamous cell carcinoma specimens. Longitudinal, repeated samplings from a high risk patient who persistently showed high grade dysplasia across the bronchus, revealed that delta-θ could identify SCAs continuously across the whole genome. The fact this individual had highly overlapping SCAs between different bronchial locations indicates genomic field cancerization may occur, along with the histological field effect in premalignant epithelium.
In SNP microarray studies, delta-θ is a highly sensitive metric for detecting SCAs even in heterogeneous dysplastic bronchial specimens. SNP array may be a powerful tool to understand premalignant genetic alterations and field cancerization.
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P3.04 - Poster Session/ Biology, Pathology, and Molecular Testing (ID 235)
- Event: WCLC 2015
- Type: Poster
- Track: Biology, Pathology, and Molecular Testing
- Presentations: 1
- Coordinates: 9/09/2015, 09:30 - 17:00, Exhibit Hall (Hall B+C)
P3.04-110 - PTPRH Hypomethylation as a Prognostic Factor in Non-Small Cell Lung Cancer (ID 759)
09:30 - 17:00 | Author(s): K. Soejima
Tyrosine phosphorylation is an important signaling mechanism in cancer. PTPRH is a receptor-type protein tyrosine phosphatase thought to be a potential regulator of tumorigenesis. The aim of this study is to clarify the significance of PTPRH expression and its regulation by DNA methylation in non-small cell lung cancer (NSCLC), especially in lung adenocarcinoma.
PTPRH mRNA expression was examined in 89 NSCLC and corresponding non-cancerous tissues. The correlation between DNA methylation and PTPRH gene expression was investigated in another cohort that consisted of 145 patients with lung adnocarcinoma. Gene regulation by DNA methylation was assessed using a DNA methylation inhibitor. Statistic analysis was performed to clarify whether the DNA methylation status of PTPRH is a prognostic factor for patients with lung adenocarcinoma.
PTPRH mRNA expression was significantly up-regulated in NSCLC. PTPRH DNA methylation was reduced in lung ademocarcinomas and inversely correlated with mRNA expression. 5-aza-2'-deoxycytidine treatment of lung cancer cell lines with low PTPRH expression, restored mRNA PTPRH expression levels. Furthermore, low PTPRH methylation was associated with shorter recurrence-free survival (P < 0.0002) and overall survival (P < 0.0001). Multivariate analysis revealed that PTPRH DNA methylation was an independent prognostic factor (P < 0.01).
We confirmed that PTPRH is overexpressed in NSCLC. In addition, we determined that hypomethylation of PTPRH is a poor prognostic factor in lung adenocarcinoma.