176 Background: Cabazitaxel (CBZ) improves overall survival in mCRPC that progresses during or after docetaxel treatment. CABASEM is a phase II study to evaluate the efficacy and safety of a weekly schedule of CBZ for 'unfit' (ECOG2, previous neutropenic fever with docetaxel, or radiotherapy to <25% of areas of bone marrow reserve) mCRPC patients after docetaxel failure. Fragility scales were performed to patients included before treatment and results are described. Methods: All 70 patients were treated with CBZ 10 mg/m2/wk 4 administration every 5 weeks. Geriatric fragility scales performed were Lawton daily day activities (ADL), BPI score, Katz instrumental daily day activities (IADL) and Charlson index. General and specific items have been analyzed in relation with toxicity and efficacy (clinical benefit (OR+SD), PSA response, composite PFS, PSA-PFS, and overall survival) in all patients and in older than 70 years. Results: Median age 73 (range 54-85). Charlson index and ADL scale had not relationship with any toxicity observed and any efficacy outcome in the whole group nor in older than 70. IADL independence grade was related to survival in the whole group (p=0,025) and older than 70 (p=0,02). In the whole group, some IADL items were associated with PSA response (buying, p=0.003; cooking, p=0.06; and IADL independence grade p=0.01), PSA PFS (telephone use, p=0.01; handle finances, p=0.06), composite PFS (telephone use, p=0.013; housekeeping, p=0.03; handle finances, p=0,06) and OS (telephone use p=0.001; laundry, p=0.008; handle finances, p=0.02 and IADL dependence grade, p=0.003). Only any grade diarrhea and grade 2 neutropenia was associate with buying (p=0.025) and cooking (p=0.05) IADL items respectively, in patients older than 70 years. Conclusions: IADL scale and items seem to be more related to efficacy (OS, PSA response, PFS, clinical benefit and PSA PFS) than ADL and Charlson scales in mCRPC older than 70 years treated with weekly cabazitaxel. No clear association of scales and items with toxicity were observed in this group of patients. Clinical trial information: NCT01518283.