RACGP – Lung Cancer Screening

Lung cancer is one of the most commonly diagnosed cancers in Australia and the leading cause of cancer deaths, with 8,457 deaths recorded in 2020.¹ In 2022, there were approximately 14,500 new cases of lung cancer diagnosed nationwide.¹ According to the latest statistics from the Australian Institute of Health and Welfare, more than 21,700 people were diagnosed with lung cancer between 2013 and 2017.¹ Lung cancer is often asymptomatic in the early stages, with 65% of cancers developing at stage 3 or 4.² As a result, many patients are diagnosed with advanced disease and have a poor prognosis. Five-year survival rates vary widely and depend on how advanced the condition is. The five-year survival rate for stage 1 disease is 68%, dropping to 3% for stage 4 disease.³ Early detection is therefore desirable, as it significantly reduces morbidity and mortality.^Four Low-dose computed tomography (LDCT) has recently emerged as a potential screening tool for asymptomatic high-risk individuals.^5,6 The Australian Government is funding a LDCT screening program for lung cancer due to commence by 2025.⁷ In this article, we focus on the evidence for lung cancer screening using LDCT.

Table 1 summarizes lung cancer screening guidelines from various countries implemented over the past decade. These guidelines recommend screening for patients aged 50 to 80 years with a smoking history of more than 20 years. LDCT screening is performed annually to biennially without contrast and has an average radiation dose of 1.5 mSv. In comparison, a conventional diagnostic chest computed tomography (CT) scan delivers a radiation dose of 6 mSv, and background radiation in Australia is 1.7 mSv.⁸

Table 2 summarizes the two landmark randomized controlled trials that investigated lung cancer screening with LDCT: the National Lung Screening Trial (NLST) in the United States and the Netherlands-Belgium Randomized Lung Cancer Screening Trial (NELSON).^5,6 Screening with LDCT has significant benefits, with the NLST and NELSON trials reporting a 20% and 24% relative risk reduction in lung cancer-specific mortality, respectively. These benefits are likely due to earlier diagnosis of lung cancer. LDCT detected early stage (Ia and Ib) lung cancer in 50% and 58.6% of people screened, respectively, compared with a baseline of 13.5% in the unscreened NELSON control group.⁶ In major international screening programmes for breast and colorectal cancer, the numbers needed to screen (NNS) are 781 and 1,250, respectively.⁹ The relatively low published NNS of 320 and 130 from the NLST and NELSON trials further supports the initiation of a national lung cancer screening program in Australia.^5,6

In the NLST study, a positive screening result was defined as a noncalcified nodule/mass of at least 4 mm or other abnormality such as lymphadenopathy or effusion.^Five Positive results were seen in 24.2% of the LDCT group, leading to further imaging including follow-up CT scans and invasive procedures.^Five A concern with the NLST was the high false positive rate, which was 96.4% in the LDCT group, resulting in a diagnosis of lung cancer in 0.9% of all patients tested.^Five NELSON incorporated an additional indeterminate classification requiring follow-up CT scan.⁶ Lesions classified as indeterminate could subsequently be upgraded to positive results by considering volume and volume doubling time. As a result, 2.1% of screened patients tested positive and required referral to a pulmonologist.⁶ Of all patients tested, 0.9% were subsequently diagnosed with lung cancer, with a positive predictive value of 43.5%.⁶ This indicates that a screening program with serial CT imaging for indeterminate nodules can be implemented in cases where only a small number of patients require referral.

Early diagnosis of lung cancer leads to significant improvements in survival rates, supporting the introduction of a screening program in Australia. LDCT meets the key requirements for a good screening strategy proposed by the World Health Organisation.^Ten Lung cancer is a disease with high mortality and morbidity, and LDCT can be used to detect its latent, asymptomatic stage. LDCT has sufficient sensitivity and specificity and is relatively safe for the proposed target population, clearly defined as people with a significant smoking history.^Ten General practitioners are well placed to identify high-risk individuals who may benefit from testing and to provide counselling or referrals following a positive result.¹¹ Lung cancer screening is recommended worldwide, and general practitioners will play a key role when Australia's national lung cancer screening program is launched.