Findings from SOLARIS Trial A new phase III randomized clinical trial has found that high-dose vitamin D3, when combined with standard chemotherapy and bevacizumab, does not significantly delay the progression of metastatic colorectal cancer. 

The trial, known as SOLARIS (Alliance A021703), was led by researchers at the Dana-Farber Cancer Institute and presented at the 2024 European Society for Medical Oncology (ESMO) Congress and conducted at hundreds of cancer centers across the U.S., enrolled more than 450 patients with untreated metastatic colorectal cancer.

 Participants were divided into two groups: one received high-dose vitamin D3 in combination with standard chemotherapy plus bevacizumab, while the other received a standard dose of vitamin D3 with the same treatment regimen. 

After a median follow-up of 20 months, the researchers observed no significant difference in progression-free survival between the two groups. 

Dr. Kimmie Ng, the lead author of the study, along with co-authors Dr. Nadine McCleary and Dr. Jeffrey Meyerhardt, emphasized that the trial results suggest that high-dose vitamin D3 cannot be recommended as an additional treatment for metastatic colorectal cancer. 

"We observed no additional concerning side effects or toxicities with the use of high-dose vitamin D3," Dr. Ng stated, "but the progression of cancer was not delayed any more than with the standard dose."

 However, the findings did point to a potential benefit in patients with left-sided disease, where primary tumors occur in the descending colon, sigmoid colon, or rectuum.

For these patients, high-dose vitamin D3 appeared to show some promise, warranting further investigation. 

The results raise questions about whether the biology of left-sided tumors might make them more responsive to vitamin D supplementation, although this remains speculative at present. 

The SOLARIS trial was initiated based on earlier observational studies that linked higher levels of vitamin D in the blood with improved survival in patients with metastatic colorectal cancer.

Researchers had hypothesized that supplementing standard therapy with high doses of vitamin D3 could enhance progression-free survival. Unfortunately, the trial’s findings did not support this hypothesis in the broader patient population. 

These results carry significant implications for the future management of metastatic colorectal cancer. While vitamin D has long been considered beneficial for overall health, its role as an adjunct to cancer treatment remains unproven. 

The study highlights the need for further research into patient subgroups, such as those with left-sided disease, to determine whether targeted vitamin D supplementation could have a more focused impact. 

The SOLARIS trial offers a critical insight into the limitations of high-dose vitamin D3 in treating metastatic colorectal cancer. Despite its promise, high-dose vitamin D3 has not demonstrated a clear advantage over standard dosing in delaying cancer progression, suggesting that it should not be recommended as a standard addition to chemotherapy and bevacizumab. 

Further research may clarify its role in specific patient groups, but for now, the findings urge caution in adopting this approach in clinical practice.