Randomized controlled clinical trials (RCTs) in oncology enroll patients who meet strict protocol-specified criteria. Many of these criteria overlap across multiple RCTs. A vast proportion of patients with metastatic cancer do not meet such criteria. Hence, patient populations encountered in clinical practice are essentially different from RCT-populations, questioning the representativeness of these trials. A real-world evidence approach, using data from clinical practice, is increasingly employed to complement the information on drug safety and efficacy obtained from traditional clinical trials.