The Cholesterol Treatment Trialists’ (CTT) Collaboration was established in 1994 after it was recognised that no single randomised controlled trial of a lipid intervention would have enough participants to enable reliable assessment of mortality outcomes or assess effects in particular types of patient.
To address this issue, the Collaboration conducts individual participant data meta-analyses of large-scale (1000 or more participants), long-term (two or more years) unconfounded, randomised controlled trials of lipid intervention treatments. To date the Collaboration has focused on assessment of statin therapy.
The Collaboration initially collected individual participant data on major vascular events, cancers and mortality as described in the original 1995 CTT protocol. The number of included trials grew over time to encompassing data from 28 major statin trials (approximately 175,000 trial participants) resulting in a series of publications which significantly impacted clinical guidelines.
In more recent years the Collaboration has collected and been analysing individual participant data on all other types of adverse events, supplemented by data on relevant laboratory values and co-medication recorded in large-scale statin trials according to a pre-specified plan published in 2016.
The aim of this project is to conduct comprehensive analyses of all the effects of statin therapy, both adverse and beneficial. This has involved a huge quantity of highly heterogeneous data, so to do this the Collaboration developed methods to convert the data into a single format using systems based on commonly used standards including the Clinical Data Interchange Standards Consortium Study Data Tabulation Model (CDISC SDTM) and the Medical Dictionary for Regulatory Activities (MedDRA).
Analyses of data on major vascular events, cancers and mortality have shown that:
- Reduction of LDL cholesterol using statin therapy substantially reduces the risk of major vascular events (major coronary events, strokes or the need for coronary revascularization) and vascular mortality by about one fifth for each 1 mmol/L reduction in LDL cholesterol achieved.
- Further reductions in LDL cholesterol with more intensive statin therapy produce further reductions in the incidence of major vascular events.
- Statin therapy has no effect on the incidence of, or death from, any type of cancer.
- Statin therapy is effective in women and men, in people with diabetes, and in those at low risk of vascular disease.
- Statin therapy reduces major vascular events in people of all ages, including those over the age of 75.