Background: Active surveillance (AS) for prostate cancer (PC) patients with low risk of PC death is an alternative to radical treatment. Vitamin D supplementation may prevent PC progression. There is no evidence for its long‐term safety and efficacy, hence its use in the care of men with PC on AS needs assessment.

Aim: Does vitamin D supplementation reduce the risk of PC progression in men with intermediate‐risk disease, during the first two years of AS?

Population: PC cases aged between 50 and 75 years will have a:

● mpMRI (centrally reviewed, not limited to any PIRADS score) and

● Gleason score=7 (e.g. Gleason grade 3 + 4) or

● 2 positive biopsy core (which may include Gleason 6) or

● Clinical stage T2 (which may include Gleason 6) or

● PSA>10 ng/mL (which may include Gleason 6)

All men with a histologically proven adenocarcinoma of the prostate will be randomised within 4 months of diagnosis.

Study Design: A double‐blinded, placebo‐controlled randomized Phase II trial.

Intervention: Men in the intervention arm will receive an initial loading dose of vitamin D supplementation (500,000 IU) followed by a monthly oral dose vitamin D supplementation (50,000 IU), while controls will receive a monthly oral placebo, for 2 years (24 months).

Follow‐up: Each participant will be followed up:

● Monthly to determine trial compliance.

● 3 monthly for PSA levels and to monitor toxicity.

● At baseline, 12‐ and 24‐ months to collect blood specimens, tissue biopsy and have a mpMRI scan.

Primary Endpoint: Active therapy‐free survival (ATFS), with no absolute requirements for conversion to ATFS.

Trial Update: ProsD commenced recruitment in April 2017 and aims to recruit 120 men. Of the 29 men invited to participate, 26 consented and have been enrolled. Of these, two men have left the trial to seek curative treatment.