Extended follow-up of the Multicentre Aneurysm Screening Study (MASS)

An aneurysm is a weakness of the wall of an artery leading to localised ballooning of that blood vessel. The commonest site is in the abdomen, hence the name ?abdominal aortic aneurysm? or AAA. In the few people with a large AAA, there is a risk of serious problems if the condition remains undetected as the artery could rupture, often without warning; about 7000 people die from this condition every year in the UK. The condition usually occurs as people get older, and is more common in men than women. The reasons why some people develop AAAs and why AAAs expand at different rates are unclear. AAAs are difficult to feel on routine examination by doctors, but can be easily, quickly and painlessly identified using ultrasound. If an AAA is found, the treatment will depend on its size. Small AAAs rarely cause problems but they do tend to slowly increase in size, and so need to be monitored. Should the AAA expand significantly, a vascular surgeon will assess the patient and decide whether surgery is indicated. The procedure involves the artery being strengthened with a tube, usually made of woven polyester. This is a major operation and, like any other operation, does carry some risks to the patient. Our work shows that through early detection and treatment, the mortality from AAAs can be halved. Continued follow-up of the large population of 67,800 men already involved in the MASS study should allow us to find out how long the benefit lasts, and to see if a single scan is sufficient to identify those at risk from the condition in the future. The UK National Screening Committee recommended a national AAA screening programme for men at age 65 to the government in February 2006. So we will be able to provide information for the programme?s implementation and development, based on high quality long-term data on the benefits and costs of screening and treatment.

The Multicentre Aneurysm Screening Study (MASS) was set up as a randomised control trial to assess: (1) the effect of screening using ultrasonography on the mortality from ruptured abdominal aortic aneurysms (AAA), (2) the quality of life of those recruited to a screening programme, and (3) costs to the NHS. A population-based sample of 67,800 men aged 65-74 were randomised to either invitation to screening or control. The initial results at four years of follow-up have been published, showing: (1) The invited group had a 42% reduction (95% CI 22% to 58%) in AAA-related mortality compared to the control group; (2) Screening did not have any major psychological impact on patients; (3) Even at four years the estimated cost-effectiveness of screening for AAA was at the margin of acceptability according to current NHS thresholds. Results of a mid-term analysis at seven years of follow-up are to be published shortly, which support the earlier findings. However, some important questions remain concerning the longer-term benefits of AAA screening, and MASS is uniquely poised to answer these. We propose to extend follow-up to 13 years, to allow continued monitoring of AAA surgery, AAA-related and all-cause mortality. As all subjects have been previously tagged for mortality surveillance at the Office of National Statistics through their NHS numbers, systems are in place for obtaining copies of death certificates and entering and analysing the data. Experienced staff are in post to manage the office databases and extract data from hospital records, patient notes and information systems. Should the collection of surgical and mortality data not continue, expertise and systems set up by the present screening programme would be lost and difficult to retrieve at a later date. An extension to follow-up will enable us to provide estimates, from directly observed data, of the long-term effectiveness and cost-effectiveness of AAA screening, as well as the incidence of aortic rupture in those with an initially normal scan.