e18813 Background: Clinical research has led to great advances that have an impact on improving the survival and quality of life of cancer patients and should be part of the standard of care. However, there is no clear evidence on whether participation in clinical trials (CTs) is cost-efficient for the national health system. For this reason, in the present study I have tried to analyse the direct impact of participation in CTs in terms of improvement in clinical results and costs. Particularly, I have looked into CT subjects diagnosed with metastatic renal cell carcinoma (mRCC) or G1-G2 metastatic neuroendocrine tumors (mNET). In addition, the potential influence of different prognostic and demographic factors on these variables has also been evaluated. Methods: Retrospectively, clinical data of the patients related to their baseline characteristics and the efficacy of the different lines of treatment they had received for their tumor were collected, as well as the direct healthcare costs derived from the clinical approach of all patients diagnosed with mRCC or mNET and clinically followed by the Ramón y Cajal University Hospital Medical Oncology Service, in Madrid, Spain, between January 2010 and February 2017. Subsequently, a comparative statistical analysis was performed of the results obtained in patients included in a clinical trial versus those who never participated in one but instead received therapy according to the standard of care (SOC). Results: Of the 104 patients (65 mRCC and 39 mNET) who were eventually included, 39 participated in a clinical trial. Overall, the 39 CT patients presented a higher overall survival (OS) than SOC patients (52 vs. 15 months. HR: 0.41; 95% CI: [0.23; 0.71]; p < 0.01), a finding that carried through in all subgroups, including age, sex and prognostic factors. Regarding healthcare costs, patients who participated in CT yielded a mean annual savings of €46,109.56 per patient (p < 0.01) compared to patients treated according to SOC, mainly due to pharmacological savings (€27,406.42). Furthermore, the savings were generalized in all subgroups regardless of age, sex and prognostic factors. Additionally, CT patients required 75.81% fewer hospitalisations (p < 0.01) with a lower associated mean cost (p = 0.02), and the mean annual cost corresponding to the use of the Emergency Service was lower (p < 0.01). Finally, the unadjusted incremental cost-effectiveness ratio (ICER) was -€14,970.64 per year of life gained (YLG) and the adjusted ICER was -€42,656.11 per life saved. Conclusions: From the national health system perspective, the participation of patients in CTs is related to an improvement in OS and savings in clinical costs in patients diagnosed with mRCC and mNET. In short, the participation of cancer patients in CTs represents a cost-efficient therapeutic option.