GP Extended Action Triptorelin

Inclusion Criteria: * Patients must give written (personally signed and dated) informed consent before completing any study related procedure. * Patients must be 18 years old or over. * Patients must have a documented diagnosis of locally advanced or metastatic prostate cancer suitable for hormonal treatment * Patients must be medically castrated with serum testosterone ≤ 0.5ng/mL * Patients must have received at least two injections of a 3- monthly LHRH agonist by the time of the screening tests * Patients must be stable on a 3-monthly LHRH agonist injection with stable PSA levels between screening and baseline (i.e. the baseline value must either be lower or less than 25% higher than the Screening value or if ≥25% higher, ≤0.5ng/mL higher than the screening value). In addition: * For patients with locally advanced prostate cancer (M0), LHRH agonist injection (any formulation) must have been initiated within the last 3 years from Baseline, * For patients with metastatic prostate cancer (M+) and a Gleason score ≤ 7, LHRH agonist injection (any formulation) must have been initiated within the last 2 years from Baseline, * For patients with metastatic prostate cancer (M+) and a Gleason score \> 7, LHRH agonist injection (any formulation) must have been initiated within the last 12 months from Baseline. * Patients must have an estimated life expectancy of at least twelve months according to the investigator's assessment. Exclusion Criteria: * Patients have had previous surgical castration or present any concomitant condition which could compromise the objectives of the study and/or preclude the protocol-defined procedures (e.g. severe medical conditions, brain metastases, psychiatric disorders, active or uncontrolled infection, known pituitary disease). * Patients are, in the opinion of the investigator, unable to comply fully with the protocol and the study instructions. * Patients have received investigational drug(s) or treatment(s) within 30 days prior to study entry or will require a concurrent treatment with any other experimental drugs or treatments or present any concomitant condition which could compromise the objectives of the study and/or preclude the protocol-defined procedures (e.g. severe medical conditions, brain metastases, psychiatric disorders, active or uncontrolled infection, known pituitary disease). * Patients have had a diagnosis of any other cancer without a history of stability/remission within five years of screening, with the exception of non-metastatic basal cell carcinoma. * Patients currently taking additional anti-androgen therapy as part of an active hormonal control therapy. * Patients scheduled to receive palliative radiotherapy during the course of the study. * Patients receiving an LHRH agonist as neo-adjuvant to radiotherapy or adjuvant to radiotherapy. * Patients receiving LHRH agonist as adjuvant to surgery. * Patients scheduled to undergo radical prostatectomy during the course of the study. * Patients with known hypersensitivity to LHRH agonists, their analogues or any or any other component of the products to be administered.