Association of promoter methylation of and mutations in non-small cell lung carcinoma in Kashmiri population (India).

BACKGROUND

Non-small cell lung carcinoma (NSCLC) incidence and progression is increasing because of genetic and epigenetic changes. The mutations in the Kirsten rat sarcoma () are the most frequently oncogene aberrations in lung carcinoma patients. A candidate tumor suppressor gene (TSG) Ras Association Domain Family 1 Isoform A (), is silenced by promoter hypermethylation in several human malignancies including non-small cell lung carcinoma (NSCLC). We hypothesized that methylation and mutations may play an important role in NSCLC.

METHODS

Non-small cell lung carcinoma patients (n = 100) and equal number of healthy controls were assessed for activating (exon 2) mutations using allele-specific oligonucleotide polymerase chain reaction (ASO-PCR) and promoter hypermethylation of using methylation specific PCR.

RESULTS

The frequency of mutations in Kirsten rat sarcoma () were found in 31% of NSCLC patients in the Kashmiri population and occur most commonly, but not exclusively, in adenocarcinoma histology and life-long smokers. The NSCLC patients in advanced stage reported the higher frequency of mutation in (exon 2). A significant higher frequency of this mutation was reported in patients with NSCLC (29.16%) who are positive for metastasis ( < 0.03). The frequencies of promoter hypermethylation at Ras Association Domain Family 1 Isoform A () were 41% in cases and 3% in control samples. The frequency of mutation and promoter methylation were significantly different between adenocarcinomas (ADC) and squamous cell carcinomas (SCC) patients with NSCLC ( < 0.03). In addition, we reported that NSCLC patients having promoter methylation was significantly associated with smoking ( = 0.01). It was identified that NSCLC patients with promoter region hypermethylation had poorer survival and faster disease progression compared with those without hypermethylation of promoter region ( = 0.0001). The Median survivals among with cases containing promoter region hypermethylation of were 17.20 and 42.13 months for patients without promoter region hypermethylation of and the patients with mutation with or without hypermethylation of the promoter region of a tumor suppressor gene had poorer survival compared with those patients with wild type gene, with or without hypermethylation of promoter region. These differences were statistically significant based on Log-rank (Mantel-cox) test ( = 0.0001). The median survivals among patients with mutation in protooncogene were 16 months and 42 months for NSCLC patients with wild type gene.

CONCLUSIONS

The aberrant gene promoter methylation with the subsequent mutation in gene (exon 2) plays a significant role in the pathogenesis and disease progression of non-small cell lung carcinoma (NSCLC).