Optimal Selenium for Bowel Polyps (OSCAR) (OSCAR)

Randomised Phase Ib Trial to Determine the Optimal Selenium Status to Prevent Colorectal Adenoma Recurrence: OSCAR

New Zealand (NZ) has high bowel cancer rates, which the Bowel Screening Programme aims to reduce by early detection of bowel cancer and its precursor, adenomas (polyps). Bowel cancer and adenoma rates are higher in countries like NZ with low intake of the essential trace mineral selenium. Overseas, trials of selenium supplements reduced adenoma recurrence in people with low blood selenium, but not with high levels (where adding selenium increased health risks). Laboratory research explained this, and found certain types of selenium are safer and more effective. The optimal type and dose of selenium to use in NZ cancer prevention trials is not known. The main objective of this trial is to evaluate which dose and type of selenium (either selenomethionine or methylselenocysteine) gives optimal selenium status to maximise cancer prevention without causing health problems from excessive selenium intake. We also want to see how much selenium is needed according to selenium blood levels before starting selenium in the trial. Side effects will be evaluated, as will recruitment rates. This will determine the feasibility of developing a large randomised trial of selenium to reduce the recurrence rates for advanced adenomas in NZ. This trial will recruit 60 patients from Middlemore and Waikato Hospitals with an advanced adenoma removed through the Bowel Screening Programme. Patients will take one selenium compound, dosed at 50 mcg/day for 6 weeks then 100 mcg/day for 6 weeks, and will have blood tests at baseline, then blood tests and evaluation of side effects at 6 weeks and 12 weeks.

50 micrograms of selenium as Selenomethionine per oral capsule. Dosage: One capsule a day for 6 weeks, followed by two capsules per day for 6 weeks.

50 micrograms of selenium as Methylselenocysteine per oral capsule. Dosage: One capsule a day for 6 weeks, followed by two capsules per day for 6 weeks.

To determine whether 50 micrograms/day of selenium for 6 weeks significantly increases plasma SEPP1 from baseline.

To determine whether the change in plasma SEPP1 from baseline is greater with selenium 100 micrograms/day than 50 micrograms/day only when baseline plasma selenium is below the median value for the trial population.

To determine whether the change in plasma SEPP1 from baseline is not different between methylselenocysteine and selenomethionine at each dose.

To determine the incidence of treatment-emergent adverse effects as classified according to NCI-CTCAE version 5.0

Inclusion Criteria: Participants will have all of the following: pathologically-confirmed advanced adenoma (defined as any one of >/= 10mm diameter, >/= 3 adenomas, high-grade dysplasia, tubulovillous or villous adenoma) 5 diagnosed at first colonoscopy in the National bowel screening programme within the previous 6 months; no residual colorectal adenomas; next colonoscopy planned within 5 years; willing and able to comply with all trial requirements, including treatment and assessments; signed written, informed consent. Exclusion Criteria: Participants will have none of the following: currently taking selenium supplements (including in multivitamins) or within the last 6 weeks; previous history of colorectal adenoma, colorectal cancer or familial colorectal cancer syndrome; other significant cancers within the last 5 years; concurrent medical conditions that, in the opinion of the investigators, would compromise either participant safety or the integrity of the data (e.g., malabsorption); male participants with a female partner of childbearing potential or pregnant, and unwilling to remain abstinent or use effective contraception (including barrier contraception with a pregnant partner).