Increased RASSF1 C Expression Correlates with Tumor Recurrence and Shorter Patient Survival in High-Grade Pulmonary Neuroendocrine Carcinomas
G Pelosi, C Fumagalli, A Sonzogni, P Maisonneuve, B Del Curto, M Manzotti, D Galetta, G Viale. European Institute of Oncology and University of Milan School of Medicine, Milan, Italy; European Institute of Oncology, Milan, Italy
Background: The Ras-association domain family 1 (RASSF1) gene regulates complex functions, such as cell proliferation, motility and apoptosis, under two promoters (1&2) and different mRNA isoforms. Little is known, however, about the role of this gene in pulmonary neuroendocrine tumors.
Design: Promoter hypermethylation, real-time PCR assay for different RASSF1 isoforms, RASSF1 A protein immunodetection, and FISH analysis for 3p21.3 loss were assessed in 58 snap-frozen pulmonary neuroendocrine tumors, including 20 typical (TC) and 11 atypical carcinoids (AC), 11 large-cell neuroendocrine (LCNEC) and 16 small-cell (SCLC) carcinomas, as well as in 20 non-small cell lung carcinomas (NSCLC) which were used as controls. Non-neoplastic lung tissue was also paired in all assays.
Results: Promoter 1 included two main CpG islands that were hypermethylated in neuroendocrine tumors but not in non-neoplastic tissue samples or NSCLC (p<0.001), with fine regulation being according to tumor grade (TC/AC vs LCNEC/SCLC, p<0.001). Island 1 but not island 2 hypermethylation correlated with down-regulation of RASSF1 A protein expression in AC (p=0.0337), and reduced RASSF1 A/E mRNA content was also observed in SCLC as compared with LCNEC (p=0.041). At variance, promoter 2 was never hypermethylated and up-regulation of its RASSF1 C transcript emerged as an adverse prognosticator in the LCNEC/SCLC group for both overall (HR: 2.271; p=0.005) and disease-free survival (HR: 1.763; p=0.0169), independent of tumor stage. Loss of RASSF1 locus at 3p21.3 did not differ between neuroendocrine tumors and NSCLC, but positive correlation was found between the FISH signal and the RASSF1 A/E isoform (p=0.023) and protein (p=0.043) expression in atypical carcionoids.
Conclusions: In conclusion, the RASSF1 gene is likely to play a relevant role in the development of pulmonary neuroendocrine tumors, with dual functions of the recessive oncogene for RASSF1 A/E in the growth of atypical carcinoids and SCLC, and of the dominant oncogene for RASSF1 C in the survival impairment of high-grade tumor patients.
Tuesday, March 10, 2009 1:00 PM
Poster Session IV # 246, Tuesday Afternoon