Hypermethylated DAPK in serum DNA of women with uterine leiomyoma is a biomarker not restricted to cancer

Abstract

Objective: Ovarian cancer is most frequently diagnosed at a late stage with a poor prognosis. No markers for early diagnosis have been established. Aberrantly methylated DNA appears as a promising molecular cancer marker. The aim of this study was to analyze the methylation status of the proapoptotic cancer related gene death-associated protein kinase (DAPK) in ovarian cancer patients, healthy controls and in patients suffering from a benign proliferative disease such as uterine leiomyoma.

Methods: Methylation-specific PCR (MSP) was used to detect DAPK methylation in primary tumor tissue and serum of both ovarian cancer (n=32) and uterine leiomyoma patients (n=17 primary tissue, n=30 serum). Serum samples from healthy women served as controls (n=20). MSP results were confirmed by restriction digest and sequencing analyses of cloned PCR products.

Results: DAPK methylation was detected in 50% and 35.3% of primary tissue and 56% and 23.8% of serum samples from ovarian cancer and leiomyoma patients, respectively. However, the association of methylation frequencies in tissue and serum was low (kappa=-0.053). Sequencing experiments revealed fully methylated MSP products in sera of both ovarian cancer and leiomyoma patients. In contrast sera from control patients showed only partially methylated DAPK sequences.

Conclusion: DAPK hypermethylation was neither specific for the tissue of origin nor for cancer. The high prevalence of leiomyoma compromises the utility of this gene as a serum marker for early ovarian cancer detection. These data emphasize the necessity to co-analyze controls presenting with non-cancer proliferative disease in the quest for molecular cancer markers.