LBA5004 Background: Up to 80% of patients receiving ADT suffer HFNS which impacts quality of life (QOL) and potentially ADT compliance. Mitigation options are limited. Prior research has found self-help CBT, with minimal guidance, reduced HFNS due to ADT at 6 weeks. We tested the longer term impact of self-help CBT, guided and delivered by prostate Cancer Nurse Specialist (CNS) teams. Methods: MANCAN2 is a multicentre randomised controlled trial and process evaluation within UK prostate cancer units. Eligibility: localised/advanced prostate cancer; on ADT with ≥ 6 months further planned; HFNS Problem Rating Scale ≥ 2. Patients were randomised (1:1) in groups of 6 to 8 to treatment as usual (TAU) or CBT + TAU, by permuted block, stratified by site, cohort and treatment intent. CBT was a 4-week self-help intervention (booklet and relaxation audio) with pre- and post-intervention group workshops by the prostate CNS team. Primary objective: does adding CBT to TAU reduce 6 month HFNS Problem Rating Scale versus baseline (mixed linear regression). Secondary endpoints: 6 week HFNS Problem Rating Scale, HFNS frequency, HFNS beliefs and behaviours, QOL (EORTC QLQ-C30, symptoms (rating scales for anxiety, depression, mood and sleep) by mixed logistic regression), ADT compliance (chi-squared test). A 6 month mean HFNS Problem Rating Scale difference of ≥ 1.5 points was deemed clinically relevant, and required data from 111 patients (90% power, 5% type 1 error, 6 to 8 patients per group, intra-class correlation 0.01, anticipating 26% patient loss). Results: 162 patients were randomly assigned (81/arm) and 117 returned 6 month HFNS Problem Rating Scale data. Baseline characteristics were balanced. Mean CBT delivery adherence was 85%. 6 month mean HFNS Problem Rating Scale score was not significantly different for the TAU alone versus CBT + TAU (mean 4.08 vs 4.04, 95% CI for difference: -0.89, 0.80; p=0.97), although a difference was observed at 6 weeks (mean 4.47 vs 3.79, 95% CI: -1.26, -0.09; p=0.03). At 6 weeks, CBT patients had higher weekly HFNS frequency (median 54.2 vs 59.4, 95% CI: 0.22, 10.19; p=0.04), lower depression score (median 7.19 vs 6.19, 95% CI: -1.88, -0.12; p=0.03) and lower anxiety score (median 4.25 vs 3.39, 95% CI: -1.64, -0.08; p=0.03). CBT patients had more positive beliefs about openness and humour scores at 6 months (median 4.92 vs 4.59, 95% CI: -0.63, -0.03; p=0.03). There was no significant difference for other measures of HFNS beliefs and behaviours, quality of life, anxiety, mood, sleep quality and treatment compliance. Conclusions: Adding CBT to TAU in prostate cancer patients receiving ADT improved short-term HFNS severity but was not maintained at 6 months. Future research should investigate whether initial CBT benefit could be made sustainable in this setting. Clinical trial information: 58720120.