201 Background: Androgen-deprivation therapy (ADT) with a luteinising hormone-releasing hormone analogue (LHRHa) is widely used in the management of prostate cancer. LHRHa suppresses testosterone to castrate levels but can lead to long term toxicities including osteoporosis, adverse metabolic effects and cardiovascular (CV) complications. Transcutaneous oestrogen is an attractive potential alternative to ADT. This approach circumvents first-pass hepatic metabolism and so should avoid the CV effects previously reported with oral oestrogen in men with prostate cancer. Castrate levels of testosterone, and hence prostate cancer outcomes, are expected to be equivalent but the side-effects associated with ADT will potentially be avoided. Methods: PATCH is a multi-centre phase II randomized study of 254 men with locally advanced or metastatic prostate cancer assigned (2:1) to either oestrogen patches (Merck FemSeven 100mcg/24hr; 4 patches changed twice-weekly, reducing to 3 after 4 weeks) or LHRHa. The primary outcome is CV morbidity and mortality, including arterial and venous thromboembolic events, acute coronary syndrome and heart failure. These have been assessed by an independent committee, blind to the treatment arm. Secondary outcome measures include PSA response, serum testosterone and also toxicities. Results: Baseline data on the 254 men will be presented including age, cardiovascular risk factors (smoking history, lipid levels and family history), and stage/grade of tumour at presentation and randomisation. CV events will be presented by randomisation arm and by treatment at the time of the event. Data relating to rates of castrate levels of hormones, PSA responses, sexual dysfunction, other toxicities (including gynaecomastia, hot flushes, anaemia and bone fractures) and compliance will also be available. Conclusions: Providing the data demonstrate that the patches are a safe and potentially efficacious therapy we propose to recruit a further 410 patients with progression-free survival as the primary outcome. CV events will continue to be closely monitored, alongside other outcomes. [Table: see text]