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MO05 - Prognostic and Predictive Biomarkers II (ID 95)
- Event: WCLC 2013
- Type: Mini Oral Abstract Session
- Track: Medical Oncology
- Presentations: 1
MO05.11 - The Effect of Two BRM Promoter Polymorphisms on the Risk of Advanced Non-Small Cell Lung Cancer (NSCLC) and Small Cell Lung Cancer (SCLC) in Smokers (ID 1987)
16:15 - 17:45 | Author(s): D. Patel
BRM, an ATPase subunit of the SWI/SNF chromatin remodeling complex, is a putative tumor susceptibility gene in lung cancer. Loss of BRM expression occurs in 15% of lung cancers. Two BRM promoter insertion polymorphisms (BRM-741 and BRM-1321) lead to epigenetic silencing of BRM and highly correlate with loss of BRM expression and function in lung tumors. Pharmacologic reversal of the epigenetic changes of BRM is feasible. We previously demonstrated a strong risk association between these two polymorphisms and susceptibility to early stage NSCLC. Here, we evaluate the association between the two BRM polymorphisms and risk of developing: 1) advanced NSCLC, and 2) SCLC among smokers.
Genotyping for BRM promoter polymorphisms was performed using TaqMan. The cohorts analyzed were: 1) 417 stage III-IV NSCLC cases and 2) 111 SCLC cases treated at the Princess Margaret Cancer Centre (PMCC), Toronto; and 3) 43 SCLC cases from the University of Florida (U of F), all with a smoking history of ≥1 pack-year. Cases were matched to healthy controls by frequency distribution (1:2 for PMCC cases; 1:1 for U of F cases) based on age, gender, pack-year smoking history, and either current smoking status (PMCC) or ethnicity (U of F). Adjusted odds ratios (aORs) with their 95% confidence intervals (CI) of the association between polymorphisms and lung cancer risk were estimated by multiple logistic regression models.
Of the 417 NSCLC cases, 59% were male; 41%, current smokers; 63%, adenocarcinoma; 51%, stage IV; median age, 63 years. The frequency of homozygosity was BRM-741, 21%; BRM-1321, 20%; both, 11%. The homozygous variants of BRM-741 and BRM-1321 were associated with an increased risk of advanced NSCLC compared to the wild types, with aOR’s of 1.6 (95% CI: 1.1-2.2; p=0.008) and 1.4 (95% CI: 1.0-2.0; p=0.04), respectively. Being homozygous for both BRM promoter variants carried an even greater risk (aOR 2.4 [95% CI: 1.4-4.0; p=0.0009]), with the strongest effect observed among current smokers (aOR 3.4; p=0.0005), and those with a histological diagnosis other than adenocarcinoma (aOR 3.2; p=0.0005). Among the 111 PMCC SCLC cases, 62% were male; 56%, current smokers; median age 65 years; of the 43 U of F SCLC cases, 35% were male; median age, 63 years. The presence of double homozygous variants of BRM-741 and BRM-1321 had no effect on the risk of developing SCLC in either of the two cohorts analyzed, with aOR’s of 1.1 (95% CI: 0.3-3.5; p=0.94) and 0.3 [95% CI: 0.04-2.41; p=0.27), respectively.
The presence of double homozygous variants of the BRM promoter polymorphisms, BRM-741 and BRM-1321, significantly increases the risk of advanced NSCLC among individuals with a smoking history greater than one year, with the strongest effect observed among current smokers. In contrast, the same two polymorphisms had no effect on the risk of developing SCLC in either of the two cohorts analyzed. Thus, this study offers further insight into potential mechanisms underlying the genetic susceptibility to developing advanced NSCLC among smokers. Validation in larger populations is warranted.
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