Older, current and former heavy smokers should receive annual, low-dose CT screening, according to revised guidelines published in the Journal of the American Medical Association on Sunday. The revised guidelines follow, and in the JAMA paper are accompanied by, a systematic review of evidence on the role of CT screening for individuals at higher risk of lung cancer.

CT (computerised tomography) or CAT scans are a type of x-ray that can detect early signs of lung cancer, but they can give false-positive results. They use a computer to create detailed images of the inside of the body.

Regular chest x-rays produce less detailed images than CT scans and can also give false-positives. They are not recommended as a lung cancer screening test because there is no evidence they save lives.

Several groups collaborated in the systematic review, namely the American College of Chest Physicians (ACCP), the American Society of Clinical Oncology (ASCO), the American Cancer Society, and the National Comprehensive Cancer Network, with input from the American Thoracic Society (ATS).

The review concludes that:

"Low-dose computed tomography screening may benefit individuals at an increased risk for lung cancer, but uncertainty exists about the potential harms of screening and the generalizability of results."

The review forms the basis of clinical practice guidelines developed by the ACCP and ASCO and was endorsed by ATS.

The revised guidelines recommend that current and former smokers aged 55 to 74 who have smoked for 30 pack years or more, and either are still smoking or have quit in the past 15 years, should be offered low-dose CT screening over both annual screening with chest x-ray or no screening.

And, this offer should only be made in settings that can deliver the comprehensive care provided to National Lung Screening Trial participants, which essentially means only centers with specialist radiologists and surgeons.

The guidelines say CT screening should not be performed on current or former smokers who have not accumulated 30 pack years of smoking, or who are outside the 55 to 74 age range.

Sick people with limited life expectancy or whose illness is not likely to be cured should also be excluded.

The JAMA report has a full account of guideline remarks and explanations.

30 pack years is the equivalent of smoking one pack of 20 cigarettes a day for 30 years. For instance, two packs per day for 15 years is equivalent to 30 pack years.

The review included a large National Cancer Institute study involving more than 53,000 people with a 30 pack year history.

The study showed that CT screening prevented about 80 deaths from lung cancer over 6 years, but 16 participants died after CT screening, including 6 who did not have lung cancer.

Lung cancer is the leading cause of cancer death both globally and in the United States, where it causes as many deaths as the next 4 most deadly cancers combined: breast, prostate, colon, and pancreatic.

Although lung cancer deaths in the US have fallen slightly since 1990, the disease is likely to kill more than 160,000 Americans in 2012.

The survival rate for lung cancer is poor, the current 5-year survival rate stands at 16%, and most people diagnosed with the disease are at an advanced stage (40% at stage IV, 30% at stage III).

Written by Catharine Paddock PhD