A randomised phase 3 clinical trial led by Dana-Farber Cancer Institute researchers in the US, conducted across several hundred cancer centres,. tested the addition of high-dose vitamin D3 to standard treatment for patients with untreated metastatic colorectal cancer.

More than 450 patients received standard chemotherapy plus bevacizumab and were randomised to high-dose or standard dose vitamin D3, according to the researchers.

The team observed no additional concerning side-effects or toxicities with the addition of high-dose vitamin D3.

However, the addition of high-dose vitamin D3 to standard treatment did not delay the progression of cancer more so than standard-dose vitamin D3, according to the team’s analysis after a median 20-month follow up.

A potential benefit for high-dose vitamin D3 was observed for patients with left-sided disease (primary tumours that arise in the descending colon, sigmoid colon, or rectum) and requires further investigation, the team of researchers noted.

The SOLARIS trial was inspired by previous research suggesting that higher levels of vitamin D in the blood are associated with improved survival for metastatic colorectal cancer and that the addition of high-dose vitamin D3 to standard therapy could potentially improve progression free survival, said the researchers.

The SOLARIS results suggest, however, that high-dose vitamin D3 cannot be recommended as a treatment for patients with untreated metastatic colon cancer, the team emphasised.