Liquid biopsies represent a non-invasive method of obtaining information about the tumor from the patient's blood, which enables the monitoring of genetic changes and the presence of tumor cells throughout the entire course of cancer treatment. They enable early detection of cancer, identification of genetic mutations for targeted treatment and monitoring of minimal residual disease (MRD), i.e. remaining tumor cells after treatment, which helps predict the risk of recurrence. Clinical trials, such as the DYNAMIC trial in colorectal cancer, have demonstrated that the use of liquid biopsies to guide adjuvant chemotherapy leads to preservation of recurrence-free survival and reduction of unnecessary toxicity in patients without detectable ctDNA. Liquid biopsies enable dynamic and repeated monitoring of treatment response in real time, which improves personalization of therapy and minimizes invasive interventions. Research also shows that the presence of ctDNA after surgery is associated with a two-fold higher risk of relapse. Despite challenges such as the variability of detectable material and the need for standardization, liquid biopsies represent a significant shift in oncology toward proactive and accurate cancer management. Their implementation can also bring economic savings in health care due to earlier diagnosis and reduced costs of invasive procedures.