188 Chapter 7 NS 0 1 2 3 4 5 case control Methylation level CDO1 (sqrt ct ratio) CDO1 a ** 0 1 2 3 4 5 case control Methylation level SOX17 (sqrt ct ratio) SOX17 b * 0 1 2 3 4 5 case control Methylation level TAC1 (sqrt ct ratio) TAC1 c Figure 5: Methylation levels of CDO1 (a), SOX17 (b), and TAC1 (c) measured in the urine of NSCLC patients (n=23) and healthy controls (n=60). Methylation levels are normalized to the reference gene ACTB and presented as square root Ct ratios. Case values represent the mean methylation level measured in the six collected urine samples. Outliers are indicated by bold circles located outside the whiskers of the boxplot. *p < 0.10 (suggestive evidence), **p < 0.05 (moderate evidence). Next, only one urine sample of each patient was compared against the control group by random sampling. The results of 100 sampling rounds are summarized as median p-value. Table 4 shows the discriminatory power (p-value) of each methylation marker between patients and controls when collecting one or six urine samples per patient. This comparative analysis indicated that the discriminatory power of TAC1 and SOX17 decreases when only one urine sample was taken into account, instead of six. Table 4: Statistical differences of CDO1, SOX17 and TAC1 methylation levels between NSCLC patients (n=23) and healthy controls (n=60) when collecting one or six urine samples per patient. Sample(s) CDO1 SOX17 TAC1 one (random sampling*) 0.662 0.059 0.133 six 0.711 0.030 0.059 Numbers represent p-values found when comparing methylation levels found in patients and controls using the Wald-test. *P-values of one urine sample represent the median p-value of 100 rounds of random sampling. NSCLC = non-small cell lung cancer.
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