Funding The project received a research grant from the Carlos III Institute of Health, Ministry of Economy and Competitiveness (Spain), awarded on the 2017 call under the Health Strategy Action 2013-2016 of the National Research Program oriented to Societal Challenges, within the Technical, Scientific and Innovation Research National Plan 2013-2016 (reference PI17/00914), cofunded with European Union ERDF funds (European Regional Development Fund). TD-S is funded by the Department of Health of the Generalitat de Catalunya, awarded on the 2016 call under the Strategic Plan for Research and Innovation in Health (PERIS) 2016-2020, modality incorporation of scientists and technologists, with reference SLT002/16/00308.

Background Metabolic syndrome (MS) is defined by the clustering of specific metabolic disorders in one subject. MS is highly prevalent globally and currently considered a growing public health concern. MS comprises obesity, hypertension, dyslipidaemia and insulin resistance. Mechanisms linking MS with cancer are poorly understood, and it is as yet unknown if MS confers a greater risk than the risk entailed by each of its separate components. The main objective of this study is to compare the association between MS and 14 site-specific cancer against the association between one or two individual components of MS and cancer. The secondary objective is to evaluate the time elapsed since the diagnosis of MS and the subsequent onset of cancer within the 2006-2017 period by sex. Methods and analysis A case-control study will be conducted for the main objective and a cohort of patients with MS will be followed for the evaluation of the second objective. Incident cases of fourteen types of cancer in patients ≥40 years of age diagnosed prospectively will be selected from electronic primary care records in the Information System for Research in Primary Care (SIDIAP database; www.sidiap.org). The SIDIAP database includes anonymous data from 6 million people (80% of the Catalan population) registered in 286 primary healthcare centres. Each matched control (four controls for each case) will have the same inclusion date, the same sex and age (±1 year) than the paired case. Logistic regression and a descriptive analysis and Kaplan-Meier analysis will be performed, in accordance with the objectives. Ethics and dissemination The protocol of the study was approved by the IDIAP Jordi Gol Clinical Research Ethics Committee (protocol P17/212). The study's findings will be published in a peer-reviewed journal and disseminated at national and international conferences and oral presentations to researchers, clinicians and policy makers.