Ontario Lung Screening Program Frequently Asked Questions for Healthcare Providers

Lung cancer is the leading cause of cancer death for people in Ontario. In 2022, approximately 7,000 people were expected to die from lung cancer in Ontario.^[1] That is comparable to the number of people who were expected to die of breast, colon and prostate cancers combined.^[1]

Without an organized lung cancer screening program, lung cancer is commonly diagnosed at later stages. Now we have an effective and evidence-based way to screen people at high risk of developing lung cancer so that we can find some lung cancers early, when treatment has a better chance of working.

People who are at high risk of getting lung cancer and are eligible to get screened will be offered a type of computed tomography (CT) scan that uses a smaller amount of radiation. This test is called a low-dose CT scan (LDCT).

Ontario Health recommends using LDCT to screen people at high risk of getting lung cancer. We based this recommendation on evidence from the National Institute of Health’s National Lung Screening Trial.^[2] The trial showed a 20% relative reduction in lung cancer mortality over 6 years for those screened with LDCT.^[2] The trial also found more lung cancers at an early stage relative to cancers diagnosed outside of the trial. For more information see the article, Reduced lung-cancer mortality with low-dose computed tomographic screening.

The risk assessment to determine eligibility for the Ontario Lung Screening Program is done using a risk calculator, which is based on a statistical risk prediction model that gives an estimate of someone’s risk (as a percentage) of developing lung cancer in the next 6 years.^[3]

The risk calculator is used to determine eligibility for lung cancer screening in the Ontario Lung Screening Program because its risk prediction model has been demonstrated to be more sensitive (more effective in detecting a cancer or pre-cancer in people who have that cancer) and have a higher positive predictive value (more people are diagnosed with cancer in those that are identified as high risk by the model) than the criteria used in large randomized controlled trials such as the National Lung Screening Trial. Eligibility in the National Lung Screening Trial was based on age, pack-years (number of packs of cigarettes someone smoked per day multiplied by the number of years they smoked) and the time since someone stopped smoking.^[2] By using a more sensitive risk prediction model to choose participants, the Ontario Lung Screening Program identifies people who are most likely to develop lung cancer and who are therefore most likely to benefit from lung cancer screening.^[3]

While screening can help find lung cancer early, screening tests are not perfect and can have potential harms. If someone is at high risk of getting lung cancer, the potential benefits of finding cancer early are probably greater than the potential harms of screening. When making a decision to screen, it is important for people to think about the potential benefits and potential harms and their own values and preferences.

Potential benefits

• Getting screened regularly with a low-dose CT (LDCT) scan can find lung cancer earlier which may mean that:
  • the chance of dying from lung cancer is lower
  • treatment may have a better chance of working
  • fewer treatments may be required and the treatments may be less invasive (easier to handle)
• Screening can be part of taking an active role in protecting someone’s health and can be reassuring for some people

Potential harms

• False-positive results (i.e., when someone has an abnormal LDCT screening result, even though they do not have cancer)
• Over-diagnosis (i.e., identifying a cancer that would not have caused someone harm if they had not been screened)
• Missed lung cancers (i.e., cancer not found during an LDCT scan or grows in between scans)
• Harms from radiation exposure and other procedures that may be needed

Screening with LDCT can find lung cancer at an early stage, when treatment has a better chance of working. The amount of radiation someone is exposed to through an LDCT for lung cancer screening is:

• several times that of a chest X-ray^[4]
• much less than that of a diagnostic chest computed tomography (CT) scan^[4]
• approximately the same as 1 year of natural background radiation (radiation from the sky and the ground, and through breathing, eating and drinking)^[5]

Therefore, LDCT minimizes the potential harms of screening for people who are otherwise healthy.

People who participate in screening may have many scans over time, so it is important to keep their radiation dose as low as possible. Although the lower dose of radiation in an LDCT scan produces less detailed images than a diagnostic CT, LDCT is good at finding small lung nodules. However, a diagnostic quality CT and/or other tests are needed to accurately diagnose and stage lung cancer.

People who have been exposed to second-hand smoke or used other kinds of tobacco, such as cigars, pipe tobacco, chewing tobacco or e-cigarettes, are not eligible for lung cancer screening through the Ontario Lung Screening Program at this time unless they have also smoked a lot of cigarettes. The program will continue to monitor the evidence and may make updates to its scope in the future.

Only people who have smoked a lot of cigarettes for many years may be eligible for the Ontario Lung Screening Program because cigarette smoking is the biggest risk factor for lung cancer. In Ontario, it is estimated that cigarette smoking accounts for more than 70% of lung cancer cases and it is commonly reported to account for as many as 85% of new cases.^[6] By contrast, people who have been exposed to second-hand smoke have a much lower risk of getting lung cancer than people who have smoked a lot of cigarettes.

If the person you referred is not eligible for lung cancer screening, you can re-refer them in 3 years to have their risk re-assessed.

If the person's previous risk score was 1.00% to 1.99% and they experience any of the following changes, you can re-refer them for re-assessment at the time of the change:

• Started smoking again (if they had quit)
• Diagnosed with chronic obstructive pulmonary disease
• Identified a new family history of lung cancer

The Ontario Lung Screening Program is currently available at 10 hub site locations. We plan to expand the program to all level 1 and 2 thoracic surgery centres in Ontario by spring of 2026. Find requirements for level 1 and 2 thoracic surgery centres in the Thoracic Surgery Oncology Standards.

Ontario Lung Screening Program locations

Healthcare providers can refer people who meet referral criteria to any Ontario Lung Screening Program location. When Ontario Lung Screening Program expansion is completed in 2026, the program will be available in all regions in the province that have a level 1 and 2 thoracic surgery centre.

Ontario Lung Screening Program locations