RATIONALE: Prospective trials using hemi-ablation with high intensity focused ultrasound (HIFU) (Sonablate 500) have demonstrated feasibility, safety, and encouraging functional outcomes and early cancer control with 90% of men achieving trifecta status (no erectile dysfunction, leak-free pad-free continence, cancer control). However, these trials have involved small numbers of patients with men selected for good baseline function. A multi-centre prospective trial within a larger cohort of men that better represents the patient population with prostate cancer (external validity) is required.

Verification of a new therapy as favourable, or equivalent, in outcome to 'standard' care is ideally sought through comparison with another matched control group. Randomised controlled trials (RCTs) offer the best method for minimising systematic bias and revealing the true effect of an intervention or drug. However, RCTs involving treatments of localised prostate cancer have had a historically poor patient uptake, as the reference 'gold' standard of care is not known. In addition, RCTs are expensive to run and involve huge infra-structural support. A number of trials in the USA have been forced to close due to lack of recruitment. The ProStart trial in the UK has also had to close for the same reason. It has been acknowledged by the Food and Drug Agency in the USA that comparative randomized trials will be problematic in this area due to lack of physician and patient equipoise. A randomized trial may be feasible if a pragmatic design is adopted but prior to acceptance of such a design, the number of centres with expertise in this complex intervention (mp-MRI, TTPM, focal HIFU) will need to be increased.

Observational studies are a commonly used alternative to ascertain the effectiveness of a treatment. They are used to observe a treatment effect in a selected group of patients who are presumed to derive benefit from the treatment given. Although methodologically not as robust, and therefore prone to bias, they have some benefits over RCTs. The principal ones are those of enhanced external validity (many patients do not wished to be randomised and therefore refuse participation), and more rapid accrual compared to a randomised design. For this reasons, a single arm medium term follow-up cohort intervention study has been designed. At the time of writing the safety and tolerability aspects of focal therapy by HIFU are known as a result of the Phase I/II studies carried out at UCLH. The results have been presented and exist in the public domain in abstract form but have not yet been published (presented in tables above). These early studies were powered to detect a change in the proportion of men who could obtain an erection sufficient for penetration compared to their status prior to their treatment. The very low event rate for both erectile dysfunction and incontinence indicates that the 'proof of concept' has been demonstrated for focal therapy. Moreover, we can be relatively confident that, in expert hands, focal HIFU is safe. Therefore, a multi-centre study is now required involving a larger group of patients for the following reasons:

1. To evaluate medium term cancer control using histological parameters. Stage two of INDEX will evaluate conversion to radical and systemic therapies and link men to national databases to determine survival in 5 and 10 years.
2. To confirm that focal therapy can lead to low rates of genitourinary and rectal toxicity and minimal impact on quality of life within a large and more representative cohort of patients (greater precision around outcome measures).
3. To demonstrate that the skills (characterization through template prostate mapping and MRI as well as the treatment related skills) acquired by the team at UCLH are indeed transferable to other providers.
4. To calculate costs of care and to model potential cost-effectiveness in comparison to alternative therapies. If this single arm intervention study demonstrates acceptable outcomes to support the findings of the Phase I/II studies, it is anticipated that this preliminary study will lead onto a Phase III evaluation of focal therapy, prior to more widespread use of this technology.

1. Histologically proven prostate cancer on trans-rectal or transperineal template prostate biopsies.

2. Prostate biopsy (either TRUS or MRI Targeted or Template):

   • TRUS biopsy: up to burden bilateral disease with maximum 3mm one biopsy on non-dominant side is allowable.
   • MRI targeted and/or Template biopsy within 12 months of entry showing:
   • unilateral disease minimum 3mm of Gleason 3+3 or any Gleason 3+4 or 4+3 but not exceeding Gleason 4+3 overall OR
   • bilateral disease presence of clinically significant cancer on only one side (as determined by histological rules described above) Gleason ≤7 which is concordant with the MRI findings.

3. Stage T1-T2cN0M0 disease, as determined by local guidelines (radiological T3a permitted).

4. Serum PSA </=20ng/ml

5. Life expectancy of >/=10 years.

6. Signed informed consent by patient.

7. An understanding of the English language sufficient to understand