Addition of High-Dose Vitamin D 3 to Standard Treatment for Metastatic Colorectal Cancer

In the randomised phase 3 SOLARIS trial (Alliance A021703), adding high-dose vitamin D3 to standard first-line chemotherapy did NOT significantly prolong progression-free survival in metastatic colorectal cancer: median 11.8 months (95% CI 10.3–13.3; n=228) versus 10.3 months (95% CI 9.4–12.2; n=227) with standard-dose vitamin D3, one-sided log-rank P=.25. The primary endpoint was therefore not met, despite a numerically longer median in the high-dose arm. The result matters in practice because vitamin D supplementation is common among patients with cancer and is often started without the treating team's knowledge.