Liquid biopsy? A recent breakthrough in noninvasive bladder cancer surveillance

Approximately 70% to 75% of patients with urothelial carcinoma of the urinary bladder are diagnosed with nonmuscle invasive disease, including Ta and T1 tumors or carcinoma in situ. Of these patients, more than 50% experience tumor recurrence, and 10% to 15% experience disease progression. Considering the invasiveness and the cost of cystoscopic examination during several years of follow-up, simple and noninvasive detection methods such as the use of molecular biomarkers through transcriptome, proteome, epigenome, or metabolome analysis are imperatively needed [1]. Recently, liquid biopsy based on the circulating nucleic acids of tumor cells, such as analyses of circulating tumor DNA (ctDNA), circulating RNA, or microRNAs, has received enormous attention as a potential tool for realtime monitoring of disease status in cancer patients [2]. Of these, ctDNA is singleor double-stranded DNA released from primary tumors, circulating tumor cells, or metastatic tumors into the bloodstream of patients with malignancies [2]. Because ctDNA contains the same genomic alterations as the original tumor cells, researchers have great interest in using ctDNA as a tool for the diagnosis and surveillance of cancer [2]. Additionally, liquid biopsy based on ctDNA detection has the advantages of being noninvasive, being simple to acquire, having higher specificity, and having better sensitivity for application in real-world clinical practice. For instance, a group from Johns Hopkins University presented a novel technology (digital polymerase chain reaction, or digital PCR) for detecting very low amounts of ctDNA and identifying its genomic alterations in 640 patients with various types of malignancies, such as colorectal, gastric, pancreatic, and breast cancers [3]. A group from Stanford University also reported an ultrasensitive platform for quantifying ctDNA in 17 patients with non– small-cell lung cancer (NSCLC) by using deep sequencing Liquid biopsy? A recent breakthrough in noninvasive bladder cancer surveillance Editorial