Hypermethylation of TMEM240 Involved in Expression Deficiency Predicts Poor Hormone Therapy Response and Disease Progression in Breast Cancer

Background:Approximately 25% of patients with early-stage breast cancer experience cancer progression throughout the disease course. Alterations in TMEM240 in breast cancer were identified and investigated to monitor treatment response and disease progression.Methods:Circulating methylated TMEM240 in the plasma of breast cancer patients was used to monitor treatment response and relapse events. Illumina methylation arrays were used to identify novel hypermethylated CpG sites and genes related to poor hormone therapy response. Quantitative methylation-specific real-time polymerase chain reaction (QMSP), quantitative real-time reverse transcription PCR, and immunohistochemical analyses were performed to measure DNA methylation, mRNA and protein expression levels in 335 breast samples from Taiwanese and Korean patients. Kaplan–Meier curves, Cox proportional hazards regression and receiver operating characteristic curves were used to analyze 10-year survival and disease progression. The Cancer Genome Atlas (TCGA) dataset was used to investigate TMEM240 alterations in Western countries. Transient transfection and knockdown of TMEM240 were performed to determine its biological functions and its relationship to hormone drug treatment response in breast cancer cells.Results: Aberrant methylated TMEM240 was identified in breast cancer patients with poor hormone therapy response using genome-wide methylation analysis in the Taiwan and TCGA breast cancer cohorts. A cell model showed that TMEM240, which is localized to the cell membrane and cytoplasm, represses breast cancer cell proliferation and cell migration. TMEM240 protein expression was observed in normal breast tissues, but not detected in 88.2% (67/76) of breast tumors and in 90.0% (9/10) of metastatic tumors from breast cancer patients. Almost all triple-negative breast cancer patients (95.7%, 22/23) had deficient TMEM240 protein expression. QMSP revealed that in 54.5% (55/101) of Taiwanese breast cancer patients, the methylation level of TMEM240 was at least 2-fold higher in tumor tissues than in the matched normal breast tissues. Patients with hypermethylation of TMEM240 had poor 10-year overall survival (p = 0.003) and poor treatment response, especially hormone therapy response (p < 0.001). Prediction of disease progression based on circulating methylated TMEM240 was found to have 87.5% sensitivity, 93.1% specificity, and 90.2% accuracy, better than the currently used biomarkers CEA and CA-153.Conclusions: Circulating methylated TMEM240 is a potential biomarker for treatment response and disease progression monitoring in breast cancer.