Autologous control (OR = 1.49, 95 CI: 1516647 0.86?.57, P = 0.151, Table 3). However, the changed of results should be interpreted with caution as only a small subject was included in non-smokers and sputum control subgroup analysis (Table 3).and 0 to 80 (median 15 ) in the autologous controls according to the included studies. The methylation MedChemExpress CASIN frequency in cancer tissue was much higher than that in clinical controls. We also find a strong and significant correlation between tumor tissue and autologous samples of P16INK4A Madrasin site promoter methylation across studies (Correlation coefficient 0.71, 95 CI:0.51?.83, P,0.0001,). Fig. 4 demonstrates that most studies lie above the equal line between tumor tissue and controls, which illustrates the tumor tissue excess. In plasma samples, the methylation frequency ranged from 6 to 74 (median 33 ), which showed a significant correlation of P16INK4A promoter methylation with cancer tissue (Correlation coefficient 0.72, 95 CI: 0.27?.91, P = 0.0059, Fig 5A). The similar correlation was also found between the cancer tissue and sputum/BALF (Correlation coefficient 0.85, 95 CI: 0.35?.97, P = 0.0082, Fig. 5B). The strong and significant correlation between tumor tissue and clinical autologous controls indicated that detection of methylation status in the clinical samples such as plasma, sputum or BALF can be a potential method for diagnosis of NSCLC without invasion.Publication BiasA Begg’s funnel plot and Egger’s test were used to evaluate possible publication bias [13]. As demonstrated in Fig. 6, the shape of the funnel plot showed a slight 
asymmetry at the bottom, with a trend towards reporting bigger odds ratio. However, Egger’s test did not 11967625 illustrate any evidence of statistical publication bias (t = 0.78, P = 0.44).DiscussionHypermethylation of CpG inlsnds in promoter regions is one of the important mechanisms for inactivation of tumor-suppressor genes, involving apoptosis, cell cycle, DNA repair and etc. Deregulation of the cell cycle control system was considered important in the procedure of tumorigenesis. P16INK4 is known as one the most important tumor suppressor genes, which plays an important role in regulating the cell cycle. This gene generates several transcript variants that regulate the G1-S transition of the cell cycle [44]. In NSCLC, this gene product has been shown to be absence in about 32?0 of the cancer cells [45,46]. However, mutations of the P16INK4 gene are only found to be 0?0 [25], which indicating at least 22 ?0 loss expression of P16INK4 is associated with other mechanisms, including promoter hypermethylation. In NSCLC, promoter hypermethylation of P16INK4a gene which encodes a cyclin-dependent kinase inhibitor, has been found in variety of studies with a frequency of 17 [26] to 83 [23] in theCorrelation of P16INK4A Gene Promoter Methylation between Tumor Tissue and Autologous Clinical SamplesGenerally, the frequency of P16INK4A promoter methylation ranged from 17 to 80 (median 44 ) in the lung cancer tissue Table 2. Meta-regression analysis.Heterogeneity sources Control type Ethnicity Sample size Method doi:10.1371/journal.pone.0060107.tCoef.(95 CI) 20.36(20.65,0.063) 0.35(20.31,1.02) 20.0036(20.011,0.004) 20.12(20.61,0.38)t 22.4 1.07 20.96 20.p 0.018 0.29 0.34 0.t2 0.37 0.45 0.48 0.I2 Res( ) 63.77 67.72 68.83 68.R2( ) Adjusted 17.67 1.06 25.23 26.P16INK4a Promoter Methylation and NSCLCTable 3. Subgroup analysis.NSCLC Subgroup Sex Male Female Race Asia-pacific Caucasus Histo.Autologous control (OR = 1.49, 95 CI: 1516647 0.86?.57, P = 0.151, Table 3). However, the changed of results should be interpreted with 
caution as only a small subject was included in non-smokers and sputum control subgroup analysis (Table 3).and 0 to 80 (median 15 ) in the autologous controls according to the included studies. The methylation frequency in cancer tissue was much higher than that in clinical controls. We also find a strong and significant correlation between tumor tissue and autologous samples of P16INK4A promoter methylation across studies (Correlation coefficient 0.71, 95 CI:0.51?.83, P,0.0001,). Fig. 4 demonstrates that most studies lie above the equal line between tumor tissue and controls, which illustrates the tumor tissue excess. In plasma samples, the methylation frequency ranged from 6 to 74 (median 33 ), which showed a significant correlation of P16INK4A promoter methylation with cancer tissue (Correlation coefficient 0.72, 95 CI: 0.27?.91, P = 0.0059, Fig 5A). The similar correlation was also found between the cancer tissue and sputum/BALF (Correlation coefficient 0.85, 95 CI: 0.35?.97, P = 0.0082, Fig. 5B). The strong and significant correlation between tumor tissue and clinical autologous controls indicated that detection of methylation status in the clinical samples such as plasma, sputum or BALF can be a potential method for diagnosis of NSCLC without invasion.Publication BiasA Begg’s funnel plot and Egger’s test were used to evaluate possible publication bias [13]. As demonstrated in Fig. 6, the shape of the funnel plot showed a slight asymmetry at the bottom, with a trend towards reporting bigger odds ratio. However, Egger’s test did not 11967625 illustrate any evidence of statistical publication bias (t = 0.78, P = 0.44).DiscussionHypermethylation of CpG inlsnds in promoter regions is one of the important mechanisms for inactivation of tumor-suppressor genes, involving apoptosis, cell cycle, DNA repair and etc. Deregulation of the cell cycle control system was considered important in the procedure of tumorigenesis. P16INK4 is known as one the most important tumor suppressor genes, which plays an important role in regulating the cell cycle. This gene generates several transcript variants that regulate the G1-S transition of the cell cycle [44]. In NSCLC, this gene product has been shown to be absence in about 32?0 of the cancer cells [45,46]. However, mutations of the P16INK4 gene are only found to be 0?0 [25], which indicating at least 22 ?0 loss expression of P16INK4 is associated with other mechanisms, including promoter hypermethylation. In NSCLC, promoter hypermethylation of P16INK4a gene which encodes a cyclin-dependent kinase inhibitor, has been found in variety of studies with a frequency of 17 [26] to 83 [23] in theCorrelation of P16INK4A Gene Promoter Methylation between Tumor Tissue and Autologous Clinical SamplesGenerally, the frequency of P16INK4A promoter methylation ranged from 17 to 80 (median 44 ) in the lung cancer tissue Table 2. Meta-regression analysis.Heterogeneity sources Control type Ethnicity Sample size Method doi:10.1371/journal.pone.0060107.tCoef.(95 CI) 20.36(20.65,0.063) 0.35(20.31,1.02) 20.0036(20.011,0.004) 20.12(20.61,0.38)t 22.4 1.07 20.96 20.p 0.018 0.29 0.34 0.t2 0.37 0.45 0.48 0.I2 Res( ) 63.77 67.72 68.83 68.R2( ) Adjusted 17.67 1.06 25.23 26.P16INK4a Promoter Methylation and NSCLCTable 3. Subgroup analysis.NSCLC Subgroup Sex Male Female Race Asia-pacific Caucasus Histo.
