Background/Aim: Sunitinib is the current standard of care for first-line (1L) treatment of metastatic renal cell carcinoma (mRCC). Previous studies suggest that a modified treatment schedule may benefit patients. Our aim was to evaluate efficacy and safety regarding sunitinib treatment modification in 1L treatment of mRCC. Materials and Methods: Data were drawn from STAR-TOR, a German real-world registry to evaluate outcomes of patients with mRCC who received 1L sunitinib. Patients were divided into two groups: subsequent treatment modification (SM) or remaining on standard dose/schedule (SS). Time on treatment (TT), progression-free survival (PFS), and overall survival (OS) were estimated. Results: Overall, 297 patients were analyzed; 33% underwent treatment modification. Significant baseline differences between groups were observed; SM patients were older and had a more favourable Karnofsky performance status. SM patients achieved better outcomes than SS patients for median TT (15.1 versus 3.9 months; p〈0.0001), PFS (15.1 versus 6.0; p〈0.0001), and OS (38.1 versus 13.7; p〈0.0001). Diarrhoea (34%/17%), fatigue (30%/11%), hand-foot syndrome (28%/10%), and stomatitis (20%/6%) were more frequently reported in SM versus SS; incidence was reduced following schedule/dose modification (except diarrhoea). Conclusion: In addition to AE mitigation, sunitinib treatment modification may help improve efficacy outcomes in mRCC by prolonging treatment duration.