FISH tests for ALK and ROS1 can be applied to different biological specimens—biopsies or cytological samplesdetermination of EGFR T790M in tumor tissue and in cfDNA are both valid alternatives; if EGFR T790M testing in plasma is negative, a new biopsy is recommended whenever possible; EGFR can be detected in plasma with a high prevalence, reflecting the landscape and heterogeneity of primary tumors and metastases. The gene discussed is EGFR; the disease is neoplasm.