Vitamin D Levels Linked To Breast Cancer Survival

Low vitamin D concentration at diagnosis predicts poor survival in patients with breast cancer

  • Date: 15 Nov 2016
  • Author: By Lynda Williams, Senior medwireNews Reporter
  • Topic: Breast Cancer

medwireNews: Data analysis of the Pathways Study indicates that breast cancer prognostic features and patient survival are independently associated with serum levels of 25-hydroxyvitamin D (25OHD) at diagnosis.

“Our findings from a large, well-characterized prospective cohort provide compelling observational evidence on associations of vitamin D with lower risk of breast cancer morbidity and mortality”, say Song Yao, from Roswell Park Cancer Institute in Buffalo, New York, USA, and co-authors in JAMA Oncology.

The Pathways Study of breast cancer survivors included 4505 women who were diagnosed with invasive breast cancer between 2006 and 2013 and followed up at 12, 24, 48, 72 and 96 months. Using a case–cohort design, the researchers chose 1666 patients, aged an average of 58.7 years, who were representative of both race and breast cancer subtypes in the study and had 25OHD serum samples for analysis.

In all, 35% of patients had insufficient serum vitamin D (<0.0–29.9 ng/mL) and 48% of the patients were defined as vitamin D deficient (<20.0 ng/mL), the team reports.

Patients with advanced stage tumours had significantly lower baseline levels of 25OHD than those with earlier stage disease, with a mean concentration of 21.5 ng/mL in stage I patients, decreasing to 18.4 ng/mL in those with stage IV tumours.

Women in the highest tertile for serum 25OHD (≥25.10 ng/mL) had significantly better overall survival (OS) than those in the lowest tertile (<16.75 ng/mL), with a hazard ratio (HR) for death of 0.72 after adjusting for both demographical factors and the clinical prognostic factors of stage, grade and immunohistochemical subtype. Additional adjustment for treatment did not alter the HR further.

The lowest serum concentrations among premenopausal women were found in patients with triple-negative breast cancer, the authors say, at 18.7 ng/mL.

When premenopausal women were examined separately, the OS association with 25OHD concentration was enhanced to give a significant HR of 0.45 for the highest versus lowest tertiles after full adjustment for confounding factors.

And in this subgroup, both breast cancer-specific survival and invasive disease-free survival were also significantly associated with 25OHD concentration with adjusted HRs of 0.37 and 0.58, respectively.

For postmenopausal women, OS was significantly associated with 25OHD level after adjustment for sociodemographical markers (highest vs lowest tertile; HR=0.54) but was no longer so after accounting for clinical prognostic factors.

“We advise caution when interpreting our findings of vitamin D association with outcomes due to potential residual confounding, given that serum 25OHD concentrations are subject to many environmental and physiological changes”, the authors write.

However, after accounting for many such factors, they believe that the link between vitamin D and breast cancer survival may be causal through vitamin D’s anti-inflammatory properties.

While results from ongoing studies such as the VITAL trial may shed more light on the impact of vitamin D insufficiency or deficiency and cancer, they conclude that “observational studies like ours from large prospective breast cancer cohorts are valuable to advance our understanding of the relationship between vitamin D level and breast cancer survival.”

Reference

Yao S, Kwan ML, Ergas IJ, et al. Association of serum level of vitamin D at diagnosis with breast cancer survival. A case-cohort analysis in the Pathways Study. JAMA Oncol; Advance online publication 10 November 2016. doi:10.1001/jamaoncol.2016.4188

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