MASS

Published

Thompson SG, et al. "Screening men for abdominal aortic aneurysm: 10 year mortality and cost effectiveness results from the randomised Multicentre Aneurysm Screening Study". BMJ. 2009. 338:b2307.
PubMed • Full text • PDF

Clinical Question

What is the long term mortality benefit and cost effectiveness of screening men 65-74 for abdominal aortic aneurysms?

Bottom Line

Ultrasound (US) screening for abdominal aortic aneurysms (AAA) in men 65-74 lead to a reduction in number of deaths related to AAA after 10 years. The cost benefit of screening increases with time.

Major Points

Men older than 65 are at a increased risk for death from ruptured AAA. US is a potentantial modality for non-invasive screening for AAA, which may reduce mortality through preventive surgical repair. Results of a 1995 pilot study indicated the feasibility of population screening by US. A large clinical trial demonstrating efficacy of the intervention was needed.

The Multicentre Aneurysm Screening Study (MASS) was a randomized trial involving 67,800 men 65 to 74 years of age from 4 centers in the UK, with the original data being published in 2002. Participants were randomized into either an "invited" group that would be offered screening, or a "control" that would not be offered screening. Men who found to have an aneurysm greater than 5.4 cm or growth greater than 1 cm in a year were referred to a vascular surgeon. After 4.1 years follow up, there were 65 aneurysm-related deaths (absolute risk 0.19%) in the invited group, compared with 113 (0.33%) in the control group (risk reduction 42%, 95% CI 22–58; P<0.001).

Following the study, a national screening program for AAA was introduced in the UK. Some uncertainties remained regarding the long term mortality benefit and cost effectiveness. This 2009 paper was a 10 year follow up of MASS and was carried out to provide evidence for the long term benefit of screening. After 10.1 years, 155 deaths related to AAA (absolute risk 0.46%) occurred in the invited group compared with the 296 (0.87%) in the control group (relative risk reduction 48%, 95% CI 37%-57%). The study also examined the cost effectiveness of screening. The cost per person from screening, elective and emergency surgery in the invited group was £208 compared with £108 in the control group. The extent of reduction in the number of deaths related to AAA in the invited group led to an estimated incremental cost effectiveness ratio of £7,600 per life year gained over the 10 years of the trial. This estimate is below the guideline figure of £25,000 per life year gained determined by the National Health Service, indicating the program is cost effective.

As a result, screening is recommended and provided for all men over 65 in the UK. Data from this study has been used to develop screening programs in Sweden, New Zealand and the United States.

Guidelines

USPSTF AAA screening (2014, adapted)

• One-time US screening for AAA by US in men aged 65 to 75 years who have ever smoked (grade B)

Design

• Multicenter, randomized, open label, controlled trial
• N=67,770
  • Invited for screening (n=33,883)
  • Control (n=33,887)
• Setting: 4 centers in the UK
• Enrollment: 1997-1999
• Mean follow-up: 10.1 years
• Analysis: Intention-to-treat
• Primary outcome: Aneurysm mortality

Population

Inclusion Criteria

• Male
• Age 65-74

Exclusion Criteria

• Terminally ill or serious medical problems
• Previous aortic aneurysm repair
• Declared unfit for screening by family physician

Interventions

• Randomized to invited (US screening for AAA) or control (no AAA screening)
  • Men who had a normal aorta (<3 cm diameter) and those whose aortas were not visualized were not re-scanned
  • Patients with an aortic diameter of 3·0–4·4 cm were re-scanned at yearly intervals
  • Those with an aortic diameter of 4·5–5·4 cm were re-scanned at 3-monthly intervals
• Patient whose aortic diameter was 5·5 cm or more, or whose aortic diameter expanded at a rate of 1 cm or more within 1 year were referred to a vascular surgeon

Outcomes

Comparisons are invited group vs. control group. Statistics were only partially reported.

Primary Outcomes

Aneurysm mortality

0.46% vs. 0.87% (HR 0.52; 95% CI 0.43-0.63)

<30 days after elective surgery: 0.06% vs. 0.04%

Ruptured AAA: 0.32% vs. 0.74%

Other ruptured aneurysm 0.07% vs. 0.09%

Secondary Outcomes

Any AAA rupture

0.58% vs. 1.10%

Nonfatal: 0.12% vs. 0.23%

CV mortality

CAD: 6.86% vs. 7.22%

Other: 4.22% vs. 4.10%

All-cause mortality

30.9% vs. 30.3% (HR 0.97; 95% CI 0.95-1.00)

Additional Outcomes

Complete follow-up, those with AAA detected on initial screening

72%

Loss to follow-up for mortality, all participants

2.7%

Mean age of death

75.0 vs. 75.4 years

Adverse Events

• 25 ruptures and 19 deaths occurred in men who had initial normal scans; most of these ruptures occurred between years 8 and 10.1

Criticisms

• Unclear if there is benefit in screening men over the age of 74.
• The absolute benefit per person was small. Mortality declined from 1% to 0.5% over 10 years, with the average man gaining 5 days of life.
• Screening may lead to an increased number of surgeries with associated clinically-significant morbidity and mortality, and short-term psychological harms.
• The majority of repairs in the study were complete through open surgery. Unclear if the cost effectiveness would be as favorable through endovascular repair.
• Medical costs are higher in the US so the cost-benefit ratio is likely to be less favorable.

Funding

Medical Research Council

Further Reading

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