Vitamin D levels may be part of the reason some women saw a benefit from adding a bone drug to standard breast cancer chemotherapy regimens, a researcher said.

Postmenopausal women with sufficient levels of the vitamin were significantly less likely to see their breast cancer recur in their bones when they combined chemotherapy with zoledronic acid (Zometa), according to Robert Coleman, MD, of the University of Sheffield in Sheffield, England.

On the other hand, markers of bone turnover had no impact on the risk, Coleman reported at the San Antonio Breast Cancer Symposium here.

The finding - based on an analysis of stored samples from participants in the large AZURE trial - was “quite surprising,” Coleman said.

The overall trial had found little benefit in adding the bone drug to chemotherapy, but in a prespecified analysis, postmenopausal women were shown to have a significantly lower risk of both recurrence in bone and distant recurrence to any tissue.

The question was why.

To help find out, Coleman and colleagues turned to stored blood samples given by 872 of the 3,360 participants before they began therapy. The subgroup included 606 premenopausal women and 266 who were postmenopausal.

Although the subgroup was not randomly selected, Coleman noted, its characteristics were similar to the overall cohort, and the results of treatment were similar – the postmenopausal women did better with the zoledronic acid.

The researchers looked at baseline levels of two markers of bone turnover – CTX and P1NP – as well as 25-hydroxyvitamin D (25-OHD) as a marker of bone and general health.

The 25-OHD level was deemed “insufficient” at or below 30 nanograms per milligrams of blood and “sufficient” above that. Strikingly, Coleman reported, only 10.3% of women in the subgroup had sufficient vitamin D.

On analysis, neither of the two bone turnover markers predicted outcomes, but “for vitamin D, there were quite surprising differences” in recurrence based on 25-OHD levels, Coleman said.

Specifically:

“Patients with a sufficient level of vitamin D had a better prognosis,” Coleman said, but the results – although consistent with other data – still need validation.

Nevertheless, he said, clinicians “should be measuring vitamin D, replenishing it appropriately, (but) whether vitamin D as an intervention will change outcome, I don’t know.”

Patients starting the trial were given vitamin D supplements, noted Carol Lange, PhD, of the University of Minnesota in Minneapolis, who was not part of the study, but who moderated the session at which it was presented.

But those supplements were 10 times lower than recommended levels and probably had little effect, she told MedPage Today, suggesting that “their lifestyle and their vitamin D level could predict survival.”

The study suggests “it’s a really good idea” to keep vitamin D levels high, she said.

Vitamin D “is cheap, it’s nontoxic, it’s a vital hormone,” she said, “and it can’t hurt you.”

Indeed, the study appears to be “demonstrating the importance of maintaining vitamin D levels in patients,” commented Steven Isakoff, MD, PhD, of Massachusetts General Hospital in Boston, who was not part of the study.

There is “a lot of investigation aimed at understanding vitamin D metabolism – independent of bone health – impacting cancer outcomes,” Isakoff told MedPage Today, but the picture is not yet clear.

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Primary source: San Antonio Breast Cancer Symposium
Source reference: Coleman RE, et al “Vitamin D, but not bone turnover markers, predict relapse in women with early breast cancer: an AZURE translational study” SABCS 2012; Abstract S6-4.