SOLARIS Trial Finds No Survival Benefit for High-Dose Vitamin D3 in Metastatic Colorectal Cancer

The SOLARIS phase III trial has delivered a negative primary endpoint: high-dose vitamin D3 added to standard first-line chemotherapy and bevacizumab produced no statistically significant progression-free survival benefit in patients with metastatic colorectal cancer, according to findings reported by The ASCO Post and published in JAMA. The result directly contradicts the earlier phase II SUNSHINE signal that had motivated the larger confirmatory study. For micronutrient policy and food fortification frameworks, the data force a recalibration of assumptions about dose-response relationships at the upper end of the vitamin D intake curve.

Trial design and dosing parameters

SOLARIS enrolled 455 adults across 151 US academic and community cancer centers. Participants were randomized 1:1 to receive high-dose or standard-dose vitamin D3 alongside investigator-selected mFOLFOX6 or FOLFIRI plus bevacizumab every two weeks. The high-dose arm received 8,000 IU daily during cycle 1, stepping down to 4,000 IU daily thereafter. The standard-dose comparator received 400 IU daily, matching the typical fortification baseline used in staple food vehicles. Median patient age was 59 years; 40% were women. Adherence to the vitamin D regimen was high in both arms.

Primary endpoint and biochemical verification

After a median follow-up of 20 months, median progression-free survival was 11.8 months in the high-dose arm versus 10.3 months in the standard-dose arm, yielding a hazard ratio of 0.92 and a P-value of.25. Objective response rate showed a numerical but non-significant difference: 51% versus 44%. Median overall survival was 25.6 months versus 27.0 months. Plasma 25-hydroxyvitamin D concentration at first restaging confirmed biochemical separation: 38.3 ng/mL in the high-dose group versus 23.5 ng/mL in the standard-dose group, with the gap sustained through treatment discontinuation. The intervention delivered its intended pharmacokinetic effect; the clinical readout remained flat. Grade 3+ adverse event profiles, including neutropenia, hypertension, leukopenia, peripheral sensory neuropathy, and diarrhea, were comparable across arms, with vitamin D–specific toxicities such as hypercalcemia, hyperphosphatemia, and renal calculi uncommon.

Implications for fortification rationale

The trial tests a dosing tier roughly 20 to 60 times the standard arm, and the biological marker moved into the sufficiency range without a corresponding clinical dividend in the overall population. A prespecified subgroup analysis flagged a possible PFS signal in left-sided primary tumors, which will require independent confirmation. For fortification policy, the operational takeaway is straightforward: raising intake above the sufficiency threshold in an unselected metastatic population does not, on this evidence, translate into measurable oncologic benefit at the doses tested. Researchers and policymakers tracking food-based delivery systems should treat the data as a narrowing of the therapeutic envelope, not as a repudiation of vitamin D sufficiency itself. The sufficiency-versus-supraphysiology distinction remains the relevant axis.