650 Background: AXILONG is a Pfizer observational multi-institutional retrospective study, evaluating clinical factors which could be related with a higher benefit of axitinib in pretreated mRCC patients in two pre-specified subgroups with extreme response to axitinib. Methods: Medical records from 157 patients treated in 40 Spanish hospitals with axitinib under clinical practice were retrospectively reviewed and included in the study. Of note, patients had to had an extreme response with axitinib, which means being a long responder (LR) to axitinib, defined as those patients who achieved a median Progression Free Survival (mPFS) of 9 months or longer, or refractory patients (RP) those who achieved a Progression Disease (PD) as best response. Results: In this analysis, we describe the results of a subgroup of patients who received axitinib in second-line after sunitinib, which represents the 68,2% (n=107) of the patients included in the whole study. The 55,1% (n=59) of this subgroup were LR and the 44,9% (n=48) were RP. In this sub-group of patients, the mPFS in LR was 18,7 months (95%CI; 12,9-24,4) and the overall response rate (ORR) was 43,9% (3,5% CR). Median overall survival (mOS) since the start of axitinib was 28,2 months for both sub-groups included, being 44,8 months in the LR patients and 7,3 months in the RP (95% CI, 12.79–34.65; p <0,001). In this population the 1st line mPSF was 27,2 months in LR and 10,9 months in RP (95%CI; 12,97-20,15; p ≤0,001). Conclusions: Despite the limitations of the AXILONG study there were a subgroup of patients who can be considered long responders o axitinib in whom we can obtain a high benefit in terms of efficacy, when treating with the sequence sunitinib-axitinib. Clinical trial information: NCT03538717 .[Table: see text]