In this pilot, controlled study the gene promoters of individuals with BCa were more commonly hypermethylated compared to healthy controls. The panel of genes tested was found to have 86.4% specificity and 61.4% sensitivity in the diagnosis of BCa, quite similar to the specificity and sensitivity of the RASSF1 promoter gene alone (86.4% and 52.3% respectively with OR 6.9).
Despite the relatively small sample size, the study sample reflects the disease’s demographics. In general, non-muscle invasive cancer (NMIBC) can be found in 70–80% of all BCa and only 10–30% constitute muscle invasive BCa (MIBC) [17]. In our sample 84% of the patients had NMIBC and 11% MIBC.
Regarding the diagnostic potential of the hypermethylated gene promoters’ panel of our study, the sensitivity (61%) is lower compared to the cystoscopy’s sensitivity for all kinds of BCa (68–83%) but higher compared to cytology, particularly for low-grade tumors (50%) [18]. Furthermore, the specificity is considerably higher than the cytology’s specificity for patients with low-grade cancer and comparable to the specificity of the invasive cystoscopy [4]. However, the diagnostic accuracy of the methylation of the panel of Twist Family BHLH Transcription Factor 1 (TWIST1) and NID2 genes as urine biomarker was higher than the diagnostic accuracy of our panel of genes, with 90% sensitivity and 93% specificity [19]. Similarly, a meta-analysis and systematic review of 24 articles revealed that the overall sensitivity and specificity of DNA methylation urine biomarkers was 84% and 92% respectively, higher than our results [20]. Studies by Zhang et al. and van der Heijden et al. achieved higher AUC (0.894 and 0.874 respectively) compared to our study’s AUC (0.7634) [21, 22]. However, Zhang et al. investigated the diagnostic potential of a panel of seven gene promoters in a non-Caucasian (Chinese) population, while van der Heijden et al. were focused on monitoring BCa and not on diagnosis.
But since DNA methylation varies among different human groups regarding macro- and micro-geographical scales, numerous studies from different areas are required in order to investigate the methylation profile of the patients with BCa across human populations [13, 23]. This may lead to a common panel of gene promoters that could be used worldwide to differentiate the BCa from healthy subjects but, in addition, a more individual approach may be necessary depending on subjects’ residency.
Our results also indicate that the hypermethylation of suppressor gene promoter of RASSF1 might be a potential single urine biomarker in BCa with specificity 86.4%, sensitivity 52.3% and OR 6.9. By contrast, a previous study which investigated the diagnostic accuracy of RASSF1 in BCa, showed lower specificity and sensitivity of RASSF1 than in our study (17% and 58% respectively), whereas a recent meta-analysis revealed that the risk for BCa in those individuals who have hypermethylated RASSF1 promoter in urine samples was OR = 19.82; 95% CI= [9.25; 42.45] [10, 24]. This risk was found to be higher among Mixed-race individuals (OR = 23.36; 95% CI= [8.39; 65.05]) and Asians (OR = 24.10; 95% CI= [15.01; 38.69]) and lower for Caucasians (OR = 13.99; 95% CI=[6.47; 30.25]) (all P < 0.0001). RASSF1 can constitute a fairly unique diagnostic biomarker for BCa since methylation of RASSF1 is rarely detected in normal bladder tissue [25]. Functional analysis of RASSF1 shows a potential involvement in inhibition of cell proliferation, promoting cell apoptosis and aging and the maintenance of microtubule stability. It is also known that the expression of RASSF1 is absent in many tumor cells as a consequence of the methylation of the gene promoter [25]. However, Chen et al. found that the use of a panel of genes had higher diagnostic accuracy compared to the use of a single gene promoter [19].
In our study population, the gene promoter of DAPK was hypermethylated only in one patient contrary to a meta-analysis concluding that DAPK promoter methylation was associated with BCa risk (OR:5.81; 95% CI = 3.83–8.82, P < 0.00001) [11]. Similarly, the gene promoter of TERT was methylated in only one subject with BCa; a recent study by a research group suggests that THOR (TERT Hypermethylated Oncological Region) hypermethylation is associated with disease progression and increased TERT expression, which leads to carcinogenesis [9]. To date, there are no published studies to confirm whether our results reflect a low prevalence of TERT and DAPK promoter in the Greek population.
An attempt was made to explore the diagnostic accuracy of our panel of genes for MIBC or high-grade tumors. We found a high negative predictive value of 0.86, with 0.86 specificity and 0.72 sensitivity Previous literature has sparsely investigated the value of methylation biomarkers in the diagnosis of MIBC or high-grade tumors. In a recent study, molecular analysis of the methylation profile of the promoters of p14ARF, p16INK4A, RASSF1A, DAPK and APC from urine sediments demonstrated correlations with BCa grade and stage [7], while other researchers found that the progression to MIBC in patients with primary pTaG1/2 BCa could be predicted with the methylation analysis of the gene promoters TBX2 and TBX3 [26].
Finally, 13.6% of our study controls had methylated the RASSF1 gene promoter, in accordance with a previous survey, which showed that 12% of the loci in apparently normal urothelium from cancerous bladder tissues were hypermethylated, indicating an epigenetic field defect [27].
In the control group, we detected DNA in 63% of the urine samples, which can be explained by the decreased cell exfoliation of normal urothelium [28]. Furthermore a recent study shows that the procedure for collection of urine sediments can be influenced by the co-sedimentation of normal cells and the presence of crystals and substances that may inhibit downstream PCR analyses [29].
Finally, our study was adequately powered and achieved an OR (6.9) higher than the initially desired OR = 4. The attained sample size of the control group was almost half of the initially planned. This might have had an effect on the genes with nonsignificant results especially for APC where methylation was 34% as opposed to 13.6% of the control samples.
Cost-effectiveness is always an issue with novel technologies. The detection of hypermethylation of specific genes from urine samples has been previously shown to be cost-effective in the diagnosis of BCa [20][30]. When using our panel of genes, the real costs were significantly lower than cystoscopy costs in the Greek National Healthcare System (89 Euro vs. 230 Euro). However, the cost-effectiveness needs to be examined in light of the diagnostic accuracy of our panel of genes which remains to be proven in larger longitudinal case-control studies.