• Mercy Medical Center, Baltimore, MD 21202, USA. khelzlsouer@mdmercy.com

The Cohort Consortium Vitamin D Pooling Project of Rarer Cancers (VDPP) brought together 10 cohorts to conduct a prospective study of the association between vitamin D status, measured as serum concentrations of 25-hydroxyvitamin D (25(OH)D), and the development of 7 rarer cancer sites: endometrial, esophageal, gastric, kidney, non-Hodgkin lymphoma, ovarian, and pancreatic cancers. The cohorts come from 3 continents, with participants from a wide range of latitude who are racially diverse. Across each cancer site, there was no evidence of a protective association between higher concentrations of 25-hydroxyvitamin D (>75 nmol/L) and cancer outcome. An increased risk at very high levels (> or =100 nmol/L) was noted for pancreatic cancer, confirming previous reports. The articles included in this issue detail the overall design and governance of the project, correlates of vitamin D status, and results from the cancer site-specific investigations. The Vitamin D Pooling Project realizes a major goal of consortium efforts, namely, to rigorously test hypotheses for rarer cancer outcomes that may not be adequately addressed in any one prospective cohort study. The results of this study have application for the planning and conduct of intervention trials, especially in determining potential risks.