Is There an Ace Up One's Sleeve in the Preanalytical Phase of the Circulating Tumor DNA Analysis?

Circulating tumor DNA (ctDNA) analysis has emerged as a pivotal minimally invasive tool for early detection, monitoring, and treatment stratification in cancer patients. However, the accuracy and reliability of ctDNA assays are profoundly influenced by preanalytical variables. This review discusses the impact of biological features (circadian rhythm, age, and sex), lifestyle factors (diet, smoking, and physical activity), as well as technical aspects such as hemolysis, leukocyte lysis, and delayed plasma separation on ctDNA integrity and concentration. Fluctuations in ctDNA levels driven by these factors highlight the need for clear guidelines regarding precollection timing, dietary restrictions, and sample processing. Furthermore, the adoption of harmonized protocols is essential to reduce variability and improve reproducibility across clinical and research settings.