Distinct DNA methylation epigenotype in bladder cancer patients from different
Chinese populations and its implication in cancer detection using voided urine
samples
Student: Ming-Hsuan Tsai
Adviser: Michael W. Y. Chan
Bladder cancer is the sixth most common cancer in the world and the cancer incidence
is particularly high in southwestern Taiwan. Patients with bladder cancer would need
to have lifetime follow-up and repeated urine cytology for non-invasive cancer
detection. However the sensitivity for urine cytology is known to be low especially
for low grade cancer patients. Previous studies including ours have identified several
tumor-related genes that are hypermethylated in bladder cancer patients and can be
detected in voided urine samples. However, detail methylation profile of bladder
cancer in Taiwan is currently unknown. On the other hand, studies also suggested that
the non-random methylation profile in cancer may be related to the exposure of
different environmental carcinogen in different locality. In this regard, we aim to
investigate the DNA methylation profile of multiple tumor suppressor genes in
bladder cancer patients from different Chinese populations including Taiwan (104
cases), Hong Kong (39 cases) and China (Beijing, 24 cases) by methylation-specific
PCR (MSP). Our data showed that frequent methylation was detected in p14 (61.8%),
DAPK (51.0%), SFRP1 (47.5%), and IRF8 (46.6%) from cancer patients of Taiwan.
While methylation also detected in APC (41.4%), hMLH1 (37.5%), RASSF1A
(32.7%), p15 (24.5%), SOCS-1 (24.0%), and E-cadherin (21.2%). Interestingly,
methylation of E-cadherin, hMLH1, p14 and p15 showed obvious diversity among
samples from Taiwan, Hong Kong and China. On the other hand, methylation profile
from Taiwan demonstrated a bimodal distribution which is a characteristic of CpG
island methylator phentotype (CIMP). Besides, the degree of methylation were
significantly correlated with pathological grade (P<0.001) and stage (P<0.05).
Furthermore, patients with APC or RASSF1A methylation was significantly associated
with shorter recurrence-free survival than those without methylation
(Gehan-Breslow-Wilcoxon test, P=0.014 and 0.037 respectively). We then
investigated the feasibility of using DNA methylation as urine biomarkers for cancer
detection. The sensitivity and specificity of detecting any one of the methylated gene
(IRF8, p14 and SFRP1) in voided urine of patients using qMSP is 86.7% and 94.7%
respectively. In conclusion, our data indicated that there are distinct DNA methylation
profiles among different Chinese populations. These profiles demonstrate gradual
increases with cancer progression and could be served as a potential relapse indicator.
Finally, detection of DNA methylation in voided urine with these distinct DNA
methylation markers is more sensitive than urine cytology.