Akutsu T, Okada S, Hirooka S, et al. - Researchers performed post hoc analyses of the AMATERASU randomized trial of vitamin D3 supplementation (2,000 IU/day; UMIN000001977), to further determine the influence of subgroups stratified by expression levels of p53, vitamin D receptor (VDR), and Ki-67 on the potential benefit of vitamin D already observed in a subgroup of patients with digestive tract cancer in AMATERASU trial. Relapse-free survival (RFS) was considered as the primary outcome. The 5-year RFS observed in a subgroup of patients with p53-positive cancer (n = 226) was 79% vs 57% in the vitamin D group vs in the placebo group, respectively. The 5-year RFS estimated in a subgroup of patients with p53-negative cancer was 72% vs 84% in the vitamin D group vs placebo group, respectively. They noted that effect modification by p53 positivity was significant. However, VDR or Ki-67 did not cause significant effect modification. Based on these findings, experts hypothesized that an improved RFS in patients with p53-positive digestive tract cancer may be achieved via vitamin D supplementation.