Differential Methylation in CITED4: Bladder Cancer Risk Biomarker?

Authors of a genome-wide DNA methylation study of prediagnostic blood samples from participants in the Women’s Health Initiative have concluded that differential methylation in the CITED4 gene, as measured in blood, is a promising marker of bladder cancer susceptibility in postmenopausal women. The findings, reported by Kristina M. Jordahl, from Fred Hutchinson Cancer Research Center, Seattle, and colleagues, werepublished online first in Cancer Epidemiology, Biomarkers & Prevention. The authors noted that, to their knowledge, theirs “is the first study of genome-wide DNA methylation, as measured in prediagostic blood, and bladder cancer risk.”

Urinary bladder cancer is the 12th most frequently diagnosed cancer in women in the US, in whom it causes about 4,570 deaths each year. According to Jordahl and coauthors, the vast majority (94%) of bladder cancers are transitional cell carcinoma (TCC), originating in the urothelial cells of the inner lining of the bladder. About 25% of all TCC cases are the muscle-invasive subtype, associated with poor survival rates. Women are 21% more likely than men to be diagnosed with advanced disease, perhaps because symptoms of early bladder cancer can be similar to those of a urinary tract infection, the authors said.

Altered DNA methylation is an important biomarker of susceptibility to cancer, since altered methylation can both silence tumor suppressor genes and activate oncogenes, “and changes in DNA methylation are common and early events in bladder carcinogenesis,” the authors emphasized.

Women selected for the DNA methylation study were participants in the Women’s Health Initiative (WHI), which Jordahl and colleagues said comprised a prospective cohort of 161,808 postmenopausal women across the United States who were recruited from 1993 to 1998 and were 50 to 79 years of age at enrollment. Screening for the WHI had included physical measurements and collection of blood and other biological samples at baseline, and participants completed detailed health questionnaires that inquired about smoking history/status and exposure to secondhand smoke. Bladder cancer cases were identified via annual medical questionnaires, with the diagnosis confirmed by blinded physician adjudicators using standard pathologic/cytologic criteria, operative reports, and discharge information.

As of September 2012, a total of 618 WHI participants had been diagnosed with bladder cancer. Jordahl and colleagues focused on the 584 participants with the TCC subtype of bladder cancer, further excluding cases based on lack of eligible controls, diagnosis of any cancer before baseline, and insufficient amount of baseline DNA.

Genome-wide DNA methylation evaluation was performed on blood from 440 TCC subtype bladder cancer cases (using prediagnosis blood samples) and 440 matched cancer-free controls from the WHI cohort. The investigators used conditional logistic regression models to test for associations between methylation measurements at 361,184 CpG sites and bladder cancer risk. (CpG dinucleotides [cytosine and guanine connected by a phosphodiester bond] mutate at a high rate.)

Jordahl and colleagues found that “[i]ncreased methylation at cg22748573, located in a CpG island within the CITED4 gene, was associated with an 82% decreased risk of bladder cancer after adjusting for race/ethnicity, smoking status, pack-years of smoking, and leukocyte cell profile and accounting for multiple testing (OR = 0.18, q-value = 0.05). The result was robust to sensitivity analyses accounting for time between enrollment and diagnosis, race, tumor subtype, and secondhand smoke exposure.”

The authors added that despite the fact that studies have identified CITED genes as tumor suppressors, there is evidence from other research that hypermethylation of CITED4 “is associated with better cancer outcomes,” and so “the importance of the methylation change may be a marker of decreased susceptibility to the development of bladder cancer through other mechanisms.”

While the researchers emphasized that their results need to be confirmed in additional prospective studies of both men and women, they said differential methylation of CITED4, measured in blood, “is a promising marker of bladder cancer susceptibility,” and the fact that blood is an easily accessible tissue “may allow targeting of screening efforts to improve bladder cancer prognosis.”