¹⁸F-FDG PET intensity correlates with a hypoxic gene signature and other oncogenic abnormalities in operable non-small cell lung cancer

<div><p>Background</p><p>¹⁸F-fluorodeoxyglucose positron emission tomography (FDG-PET) is critical for staging non-small-cell lung cancer (NSCLC). While PET intensity carries prognostic significance, the genetic abnormalities associated with increased intensity remain unspecified.</p><p>Methods</p><p>NSCLC samples (N = 34) from 1999 to 2011 for which PET data were available were identified from a prospectively collected tumor bank. PET intensity was classified as mild, moderate, or intense based on SUVmax measurement or radiology report. Associations between genome-wide expression (RNAseq) and PET intensity were determined. Associations with overall survival were then validated in two external NSCLC cohorts.</p><p>Results</p><p>Overall survival was significantly worse in patients with PET-intense (N = 11) versus mild (N = 10) tumors (p = 0.039). Glycolytic gene expression patterns were markedly similar between intense and mild tumors. Gene ontology analysis demonstrated significant enhancement of cell-cycle and proliferative processes in FDG-intense tumors (p<0.001). Gene set enrichment analysis (GSEA) suggested associations between PET-intensity and canonical oncogenic signaling pathways including <i>MYC</i>, <i>NF-κB</i>, and <i>HIF-1</i>. Using an external cohort of 25 tumors with PET and genomic profiling data, common genes and gene sets were validated for additional study (P<0.05). Of these common gene sets, 20% were associated with hypoxia or HIF-1 signaling. While <i>HIF-1</i> expression did not correlate with poor survival in the NSCLC validation cohort (N = 442), established targets of hypoxia signaling (<i>PLAUR</i>, <i>ADM</i>, <i>CA9</i>) were significantly associated with poor overall survival.</p><p>Conclusions</p><p>PET-intensity is associated with a variety of oncogenic alterations in operable NSCLC. Adjuvant targeting of these pathways may improve survival among patients with PET-intense tumors.</p></div

Genetic analysis of study group.

<p>(a) Selected genes upregulated in high PET intensity tumors (fold-change high vs. low >2, p<0.05). (b) Kaplan-Meier survivor curve representing overall survival (in months) for patients with high PET-intensity tumors (N = 11), medium intensity tumors (N = 13), and low intensity tumors (N = 10). (c) The most significantly enriched genes in PET-high tumors (p<0.05, fold change>2.0) were interrogated by DAVID gene ontology pathway analysis [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0199970#pone.0199970.ref024" target="_blank">24</a>]. Significant functional groups are shown. P-values are quantified as log units. (d) Average rank-based GSEA results for MSigDB Hallmark pathways. (e) RNA levels of core glycolysis enzymes (red) versus all genes (gray) in PET high (y axis) versus low (x-axis) tumors. “Core” enzymes were labeled such according to the KEGG gene set database.</p

Validated radiogenomic abnormalities in two cohorts of patients with early-stage NSCLC.

<p>(a) The most significantly enriched genes in PET-intense tumors (p<0.05, fold change>2.0) were selected from the study and PET validation cohort. Selected genes that overlapped are displayed in the table. (b) Average rank-based GSEA results for all pathways in the MSigDB database that were enriched in high-intensity tumors in both the study and PET validation cohorts and (c) quantified relative to hypoxia. (d) Kaplan-Meier survivor curves and log-rank test of <i>HIF1A</i> expression in prognostic validation cohort (N = 442) using median gene expression as cutoff to divide low and high expression.</p

Patient clinical characteristics.

<p>Patient clinical characteristics.</p

Patient demographics.

<p>Patient demographics.</p

Kaplan-Meier survivor curves and log-rank test of selected targets of HIF signaling in prognostic validation cohort (N = 442) using median gene expression as cutoff to divide low and high expression.

<p>Downstream targets of HIF including (a) <i>GLUT3</i>, (b) <i>ADM</i>, (c) <i>CA9</i>, and (d) <i>PLAUR</i> were associated with worse survival. Genes were selected according to validated MSigDB gene sets related to hypoxia signaling.</p