Although not employed in the clinic as of yet, microfluidic systems are likely to become a key technology for cancer diagnostics and prognosis. Microfluidic devices have been developed for the analysis of various biomarkers including circulating tumor cells, cell-free DNA, exosomes, and proteins, primarily in liquid biopsies such as serum, plasma, and whole blood, avoiding the need for tumor tissue biopsies. Here, we summarize microfluidic technological advances that are used in cancer diagnosis, prognosis, and to monitor its progression and recurrence, that will likely lead to personalized therapies. In some cases, integrated microfluidic technologies, coupled with biosensors, are proving to be more sensitive and precise in the detection of cancer biomarkers than conventional assays. Based on the current state-of-the-art and the rapid progress over the past decade, we also briefly discuss the next evolutionary steps that these technologies are likely to take.