The overall aim of this trial, which is called STAMPEDE, is to assess novel approaches for the treatment of men with prostate cancer who are starting long-term ADT for the first time, termed hormone-naïve prostate cancer. This trial aims to see if we can improve the way in which prostate cancer is currently managed, either by adding new treatments to the standard approach or by modifying the type of hormone therapy aiming to improve quality-of-life by reducing the side effects of treatment. Each new treatment approach is compared against a control arm receiving the current standard treatments. We aim to identify treatment strategies that enable men to live longer, or as long but with an improved quality-of-life, as well as offering value for money for the health service.

Since opening to accrual in Oct-2005, the trial has tested many ways of treating prostate cancer and some results are now already known. More than 10,000 men will join the trial with answers becoming available throughout the trial. New patients joining the trial from Protocol version 17.0 onwards (activated in December 2018) may be eligible to join one of two treatment comparisons, metformin (treatment group K; the "metformin comparison") and transdermal oestradiol (treatment group L; the "transdermal oestradiol comparison"). A computer program will be used to allocate which treatment each participant receives, using a chance process.

Summary of the research arms in STAMPEDE trial platform Summary of research treatment groups currently open to recruitment (June 2017)

1. Metformin (Arm K): This anti-diabetic medication is proposed to have both anti-cancer effects and may help prevent the adverse metabolic effects of long-term ADT. STAMPEDE will investigate whether adding metformin to the current standard-of-care for non-diabetic men can improve all-cause survival.
2. Transdermal oestradiol (Arm L): This is an alternative form of hormone treatment which has been shown to suppress testosterone as effectively as standard ADT and avoid some of the side-effects. It may also help to avoid the adverse metabolic effects and fatigue and therefore improve overall quality of life compared with standard forms of ADT. STAMPEDE will investigate whether transdermal oestradiol can treat the cancer as well as current standard forms of ADT.
3. Control group (Arm A): Patients allocated to this group receive the current standard-of-care ADT +/- RT +/- docetaxel.

STAMPEDE (also known as MRC PR08) is a multi-arm multi-stage (MAMS) randomised controlled trial recruiting in the UK and Switzerland. It aims to evaluate multiple therapeutic strategies in the management of high-risk locally advanced and metastatic hormone-naïve prostate cancer. Each novel treatment strategy is compared against a single, contemporaneous control arm. When the trial originally opened in 2005 there were 6 research arms enabling 5 randomised comparisons. Each comparison is evaluated in stages with pre-planned interim analyses after which recruitment may be halted should the experimental treatment fail to reach a "hurdle" of activity. Patient data from all arms and all stages are, however, included in the final analyses of the primary outcome measure, even if the investigational arm did not proceed to the final stage.

Providing sufficient activity is demonstrated, recruitment continues to the final stage and then an assessment of efficacy is determined based on the primary outcome of overall survival. Patient data from all arms and all stages are included in the final analyses of the primary outcome measure, even if the investigational arm did not proceed to the final stage.

The original comparisons which have all now been reported, evaluated a bisphosphonate (zoledronic acid), a cytotoxic chemotherapeutic agent (docetaxel) and a cyclooxygenase (Cox 2) inhibitor (celecoxib), as single agents or combinations. Since the start of the trial, a number of new research arms have been added to STAMPEDE over time to evaluate: abiraterone, a steroid synthesis inhibitor; prostate radiotherapy for patients with newly diagnosed metastatic disease; enzalutamide, an inhibitor of androgen receptor signalling, given with abiraterone; and metformin, an anti-diabetic medication and transdermal oestradiol, to be given as an alternative form of ADT.

Objectives:

Primary

To compare the safety and efficacy of novel therapeutic strategies against the current standard-of-care for men with high-risk locally advanced or metastatic prostate cancer starting long-term ADT for the first time.

Outline: This is a randomised, controlled, multi-centre MAMS trial platform. Patients are current randomised to 1 of 3 arms: control group (arm A), metformin treatment group (arm K) and transdermal oestradiol (Arm L). The other arms are all closed to recruitment with results known for all the original comparisons and awaited for others added since the trial commenced.

Patient population: STAMPEDE recruits both men with high-risk locally advanced prostate cancer and men with metastatic prostate cancer, all of whom must be starting long-term ADT for the first time. Patients who received previous radical treatment and are now relapsing with high-risk features are also eligible.

Follow-up: All patients are follow-up life long

Sub-studies: There are several translational sub-studies ongoing as part of STAMPEDE. Participation is optional. These currently include several translational sub-studies involving sample collection: saliva collection for germline DNA analysis, sequential circulating tumour DNA analysis and FFPE tumour block retrieval for DNA and RNA analysis. Other sub-studies include a QOL sub-study and an imaging sub-study.

Inclusion Criteria Participants must fulfil all the criteria in one of the following three categories. Additionally, all patients must fulfil the criteria in Section 4.

1. High-Risk Newly-Diagnosed Non-Metastatic Node-Negative (N0/Nx) Disease

   Both:

   • At least two of: T category T3/4, PSA≥40ng/ml or Gleason sum score 8-10

   • Intention to treat with radical radiotherapy (unless there is a contra-indication)

   OR

2. Newly-Diagnosed Metastatic Or Node-Positive Disease

   At least one of:

   • Stage Tany N+ M0
   • Stage Tany Nany M+

   OR

3. Previously Radically Treated, Now Relapsing (Prior Radical Surgery And/or Radiotherapy)

   At least one of:

   • PSA ≥4ng/ml and rising with doubling time less than 6 months

   • PSA ≥20ng/ml

   • N+

   • M+

   AND

4. General Inclusion Criteria Required For All Participants

1. Histologically confirmed prostate adenocarcinoma
2. Intention to treat with long-term androgen deprivation therapy
3. Fit for all protocol treatment and follow up, WHO performance status 0-2
4. Have completed the appropriate investigations prior to randomisation
5. Adequate haematological function: neutrophil count ≥1.5x109/l and platelets ≥100x109/l
6. Adequate renal function, defined as GFR ≥30ml/min/1.73m2
7. Written informed consent
8. Willing and expected to comply with follow up schedule
9. Using effective contraceptive method if applicable

1. Medical contraindications to the trial medications are given in Section 6
2. For WHO performance status definitions see Appendix A

5. General Exclusion Criteria

Patients must not fulfil any of the criteria below:

1. Prior systemic therapy for locally-advanced or metastatic prostate cancer (1) (except as listed in the protocol section 4.3)

2. Prior exposure to hormone therapy for a duration of > 12 months, or prior exposure completing < 12 months before randomisation (see section 4.3.1 for permitted prior exposure details)

3. Metastatic brain disease or leptomeningeal disease

4. Abnormal liver functions consisting of any of the following:

   • Serum bilirubin ≥1.5 x ULN (except for patients with Gilbert's disease, for whom the upper limit of serum bilirubin is 51.3μmol/l or 3mg/dl)

   • Aspartate aminotransferase (AST) or alanine aminotransferase (ALT) ≥2.5 x ULN - site must indicate at randomisation whether one or both tests are performed at site. Where both results are available both must confirm eligibility.

5. Any other previous or current malignant disease which, in the judgement of the responsible clinician, is likely to interfere with STAMPEDE treatment or assessment

6. Any surgical wound (e.g. TURP) which in the judgement of the responsible clinician may interfere with or be exacerbated by protocol treatment

7. Participant with significant cardiovascular disease, including:

   • Severe/unstable angina

   • Myocardial infarction less than 6 months prior to randomisation

   • Arterial thrombotic events less than 6 months prior to randomisation

   • Clinically significant cardiac failure requiring treatment, defined as New York Heart Association (NYHA) class II or above (1)

   • Cerebrovascular disease (e.g. stroke or transient ischaemic episode) less than 6 months prior to randomisation

   • Any other significant cardiovascular disease that in the investigator's opinion means the participant is unfit for any of the study treatments.

     1. Excluding participants receiving docetaxel as part of SOC
     2. NYHA classifications can be found in Appendix A

6. Comparison-specific eligibility criteria

In addition to the general inclusion and exclusion criteria, the following comparison-specific eligibility criteria apply.

For Randomisation to the "Metformin Comparison"

Please note from protocol v20 only patients willing to participate in the metabolic sub study should be randomised to the metformin comparison. The sub study will be conducted in a limited number of sites, see section 4.7.4 for further information.

In addition to the general inclusion and general exclusion criteria the following comparison-specific inclusion criteria must be met to be eligible for randomisation to the "metformin comparison":

• HbA1c <48mmol/mol (equivalent to <6.5%) (1)

• Adequate renal function, defined as GFR ≥45ml/min/1.73m (except for Switzerland (2))

• No history of lactic acidosis or pre-disposing conditions

• Not current or previous treatment with metformin
• No contra-indications to metformin
• No current or previous medication for treatment of diabetes
• Willingness to join the metabolic sub study

The method used to determine glomerular filtration rate may vary according to local practice.

Equations that either estimate glomerular filtration rate (eGFR) or creatinine clearance (CrCl) may be used and the same threshold value applies. Where possible, HbA1c should be performed prior to commencing SOC docetaxel to reduce the likelihood of corticosteroid-related hyperglycaemia impacting on eligibility. All participants with abnormal baseline HbA1c (i.e. 6.5% or higher) should be informed and referred to their GP for further management.

(2) Except Switzerland, please refer to SAKK appendix for local guidance

For Randomisation To The "Transdermal Oestradiol Comparison"

In addition to the general inclusion and exclusion criteria, participants fulfilling all of the following are eligible for the "transdermal oestradiol comparison":

• ≤8 weeks of anti-androgen (AR-antagonists) use

• Maximum of 1 dose of monthly or 4-weekly LHRH agonist/antagonist

• No prior LHRH agonist injection with a stated duration of effect greater than 1 month

• ≤12 weeks since first dose of any hormone therapy

• Not had a bilateral orchidectomy

• No use of cyproterone acetate (36) prior to randomisation

• No known porphyria

• No known history of deep vein thrombosis or pulmonary embolism confirmed radiologically
• No known thrombophilic disorder (e.g. Protein C, Protein S, antithrombin deficiency)
• Not yet started SOC abiraterone, enzalutamide or apalutamide