Review
Link: http://ar.iiarjournals.org/content/26/4A/2647.full.pdf
From the abstract:
"Calcitriol, the principal active metabolite of vitamin D and a naturally occurring hormone, showed significant antineoplastic activity in pre-clinical models of prostate cancer and many other tumor types. These antineoplastic effects were observed at calcitriol concentrations substantially above the physiological range."