The Pooling Project of Prospective Studies of Diet and Cancer (DCPP) is an international consortium of 39 cohort studies (see Participating Cohort Studies) established in 1991 to investigate associations between dietary and anthropometric factors and risk of cancer by analyzing harmonized participant-level data from multiple cohorts using standardized criteria across studies. To date, associations with nutrients, food groups, and anthropometric factors have been examined or are being examined with breast, colorectal, lung, renal cell, ovarian, pancreatic, prostate, thyroid, and upper aerodigestive tract cancer, and non Hodgkin lymphoma (see Publications). Recently, projects within the consortium have included evaluations of additional lifestyle factors. This project is an example of a meta-analysis of individual data as opposed to a meta-analysis of the published literature. The studies in the DCPP were initiated independently and have either completed follow-up of their participants or are ongoing.
The purposes of the DCPP are multi-fold. We evaluate whether associations are consistent across cohort studies comprised of different populations with a wide distribution of participant characteristics. The variation in study populations also allows for evaluation of dose-response relationships across a wide exposure range. For each association, we generate summary estimates which have greater precision than the individual studies due to the larger sample size. We also examine whether associations differ for specific population subgroups (ex: between men and women; among never, past and current smokers; between lean and overweight individuals) or for different histologic types (e.g. for lung cancer: squamous cell carcinomas, small cell carcinomas, adenocarcinomas) or subsites of specific cancers. These investigations are particularly important as they may identify population subgroups that may particularly benefit from specific lifestyle factors. In addition, as cancer is a heterogeneous disease, evaluation of whether associations vary by tumor subtype may lead to a better understanding of the etiology of that cancer.
To maximize the quality and comparability of the studies in the DCPP, we formulated several inclusion criteria a priori. Each study is a published cohort study which included a minimum number of cases of the specific cancer being examined. For the dietary analyses, additional inclusion criteria include 1) used a comprehensive dietary assessment method to measure usual diet and 2) assessed the validity of their dietary assessment instrument or a closely related instrument. Additional inclusion criteria have been specified for investigations of specific cancers. Currently, 39 studies are included in the consortium. However, as we become aware of new studies meeting the inclusion criteria, those studies are invited to join the DCPP.