KRAS and cancer: In the last years, an increasing number of studies demonstrate the relevance of cfDNA as an attractive tumor biomarker with great potential for the amount of information it provides about the tumor progression and prognosis as well as genetic alterations of certain cancer-related genes (BRAF, EGFR, TP53, KRAS, PIK3CA...), in a non-invasive way (1, 3, 4).