Longitudinal analysis of personal cfDNA methylome patterns in metastatic prostate cancer [plasma]

Disease progression and therapeutic resistance are hallmarks of advanced stage prostate cancer (PCa), which remains a major cause of cancer-related mortality around the world. Longitudinal studies, coupled with the use of liquid biopsies, offer a potentially new and minimally invasive platform to study the dynamics of tumour progression. Our study aimed to investigate the dynamics of personal methylomic profiles of metastatic PCa (mPCa) patients, during disease progression and therapy administration. 52 plasma samples from 9 patients with mPCa were collected, longitudinally, over 13-21 months. After cell-free DNA (cfDNA) isolation, DNA methylation was profiled using the Infinium MethylationEPIC BeadChip and analysed using the minfi software. The top 5% most variable probes across time, within each individual, were utilised to study dynamic methylation patterns during disease progression and therapeutic response. Statistical testing was carried out to identify and validate ctDNA differentially methylated genes (DMGs). Personal cfDNA global methylation patterns were temporally stable throughout disease course. A proportion of analysed CpG sites presented a dynamic temporal pattern that was consistent with clinical events, such as therapy administration, and were prominently associated with immune response pathways. Study of ctDNA identified >2,000 DMGs with dynamic methylation patterns. We concluded that longitudinal assessment of cfDNA methylation in mPCa patients unveiled dynamic patterns associated with the occurrence of specific clinical events, thus highlighting the potential of using liquid biopsies to study PCa progression. cfDNA samples were collected, longitudinally, from 9 mPCa patients. DNA was isolated and methylation was measured using the Illumina Infinium Human MethylationEPIC BeadChip. Normalized beta-values were used to compare methylation patterns, within each individual, during disease progression.