In the first randomized, blinded trial to treat cancer patients with vitamin D, a multi–institutional effort led by Dana–Farber Cancer Institute researchers has shown that high doses of the vitamin may slow the progress of metastatic colorectal cancer. The study was released online ahead of the American Society of Clinical Oncology (ASCO) annual meeting.

“We do not yet know what blood level of vitamin D is needed to see a benefit until we analyze the blood samples collected from patients enrolled on the trial,” said Kimmie Ng, MD, MPH, director of Clinical Research at Dana–Farber’s Center for Gastrointestinal Oncology. Ng will present early results from the SUNSHINE study at the ASCO conference. “In the meantime, patients can discuss with their physician about checking the levels of vitamin D in their blood, and consider taking supplements to keep the levels in sufficient ranges.”

“These data need to be confirmed in a larger study, but there does seem to be a benefit to taking high–dose vitamin D in combination with standard treatment for patients with metastatic colorectal cancer,” said Ng.

The trial followed 139 patients who were given standard–care treatment with a combination of chemotherapies and bevacizumab (which slows the growth of blood vessels that feed tumors). The patients then were randomized to receive either high doses of vitamin D (starting with 8,000 units daily for two weeks, followed by 4,000 units daily) or a control arm taking 400 units daily (a level often provided by multivitamin pills).

Participants taking the higher doses saw a median time before disease progression of 13.1 months, compared to 11.2 months in the control arm. “In the world of metastatic cancer, this difference of about two months is significant,” said Ng. Modeling to compensate for prognostic factors such as patient age and pre–existing burden of disease, the scientists found a 33 percent improvement in progression–free survival among patients assigned to the high–dose arm over an approximately 17–month median follow–up period, she said.

Other trial results showed that patients receiving high–dose vitamin D experienced severe diarrhea less frequently than those receiving low–dose vitamin D. In addition, although the comparison did not reach statistical significance, perhaps partly due to the relatively small number of patients in the SUNSHINE trial, more patients in the high–dose arm underwent surgery to remove metastatic tumors from their livers, which potentially can cure the disease.

Observational analyses of trials have generally demonstrated that higher levels of vitamin D in the blood are associated with significantly better progression–free survival and overall survival in colorectal cancer.

“We wanted to study this more rigorously with a randomized, blinded trial that could start to prove causality,” Ng said. “Our results from SUNSHINE indicate that a confirmatory larger phase III study is definitely warranted.”