Loss of PTEN Expression and Gene Copy Number in Non Small Cell Lung Cancer
Charles Leduc, Naoki Yanagawa, Mauro Saieg, Maisa Yoshimoto, Thomas John, Jenna Sykes, Melania Pintillie, Gilda da Cunha Santos, Jeremy Squire, Ming-Sound Tsao. Queen's University, Kingston, Canada; University Health Network, Ontario Cancer Institute/Princess Margaret Hospital, Toronto, Canada; Yamagata Prefectural Central Hospital, Yamagata, Japan
Background: PTEN (Phosphatase and Tensin homolog deleted on chromosome ten) which suppresses the pro-survival Akt pathway, is known to be inactivated in multiple cancers. To characterize the role of PTEN in non-small cell lung carcinoma (NSCLC), we examined PTEN expression and gene copy number loss in a large cohort of NSCLC patients and compared findings to published genomic imbalance datasets.
Design: Tissue microarrays from 153 formalin fixed paraffin embedded tumors were constructed and sections were stained with PTEN monoclonal antibody clone 138G6 (Cell Signaling Technology, Danvers, MA). Tumors with absence of immunostaining were considered PTEN negative. PTEN copy number loss was evaluated by dual-colour fluorescence in situ hybridization (FISH) in 100 tumor nuclei with in-house PTEN probe labeled with Spectrum Green and Vysis® Chromosome Enumerating Probe for chromosome 10 (Abbott Laboratories, Abbott Park, IL) labeled with Spectrum Aqua. Tumors were considered PTEN deleted if 65% of cells had < 2 copies of PTEN. Single nucleotide polymorphism (SNP) array data was mined from 757 NSCLC published datasets. The PTEN region was analyzed with the rank segmentation algorithm with thresholds for copy gain and loss of 0.4 and -0.4, respectively.
Results: Immunostaining for PTEN was negative in 41.2 % (n=63/153) of cases, more frequent among squamous cell carcinomas (26/44 or 59%) than adenocarcinomas (32/94 or 34%) (p=0.0095). Among the 133 cases with interpretable FISH results, 7 (5.2%) were PTEN deleted, including hemizygous loss in 4 cases, monosomy in 2 cases, and homozygous loss in one case. These results are consistent with the analysis of SNP datasets which also identified a low PTEN deletion rate of 5.3% (40/757). Disease-free survival was significantly poorer in patients with PTEN negative tumors by immunostaining, as compared to PTEN positive immunostaining (HR=1.71; 95% confidence interval=1.01-2.92; p=0.045).
Conclusions: Up to 40% of NSCLC do not express PTEN protein, while PTEN deletion was detected in only 5.2% of tumors by FISH. These results suggest that loss of PTEN expression in NSCLC is primarily by epigenetic or mutation. Silencing of PTEN expression appears to be a poor prognostic marker for NSCLC patients.(This work was supported by grants from the Canadian Cancer Society, Canadian Institute of Health Research and Ontario Institute of Cancer Research.)
Tuesday, March 20, 2012 1:00 PM
Poster Session IV # 307, Tuesday Afternoon