Background: We performed the 1st dose-escalation study of PSMA-targeted radionuclide therapy with ¹⁷⁷Lu-PSMA-617. Using dose-fractionation, we intended to deliver a dose-intense regimen designed to minimize radioresistance due to repopulation. Radionuclide therapy may be able to treat symptoms due to tumor and therefore may be associated with improvement in PRO. Methods: Inclusion: progressive mCRPC following potent AR-pathway inhibitor (ARPI, e.g. abi/enza) and taxane (or unfit/refuse chemo) without limit of # prior therapies, adequate organ function, ECOG performance status 0-2, without preselection for PSMA expression. Treatment was a single cycle of fractionated dose ¹⁷⁷Lu-PSMA-617 on D1 and D15 (7.4 to 22 GBq in phase 1; 22.2 GBq in phase 2). PRO tools included FACT-P and BPI-SF at baseline and follow up. Results: 44 men with median age 69 (range 55-91), median PSA 182.97 (range 0.89-5541) were treated. 93% with bone, 45% nodal, 18% lung, 9% liver, 9% other visceral metastases. 55% with at least 1 prior chemo regimen, 52% >2 prior ARPI, 27% with Ra223, 30% sip-T, 5% ¹⁷⁷Lu-J591. 59.1% with >50% PSA decline (66.7% at 22.2 GBq, n=21), median overall survival 16 months (95% CI 11-NR). High grade (Gr) toxicity was rare with 6.8% Gr 3 anemia and 2.3% Gr 3 platelets. Gr 1/2 treatment-emergent AE’s include 81.8% with pain flare, 61.4% xerostomia, 29.5% fatigue, 25% platelets, 25% anemia, 25% pain, 15.5% nausea. FACT-P scores tended to improve in all categories by D22 (1 week later), with overall FACT-P scores improving by mean of 8.9 points (p=0.07) at D22 and remaining improved at 12 wks. All BPI scores also improved, with BPI overall severity score improving by mean of 3.0 at D22 (p=0.008) and remained better than baseline at 12 wks. There was no clear association with any AE and PRO changes, but those with PSA decline tended to have improved pain scores (p=0.1). Conclusions: A single cycle of up to 22.2 GBq of ¹⁷⁷Lu-PSMA-617 is safe with fractionated (D1 & D15) dosing, with encouraging early efficacy signals in a population unselected for PSMA expression and improved quality of life and pain scores by validated PRO instruments. Clinical trial information: NCT03042468