Opinion: Why Aren’t We Screening For Lung Cancer?

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By Peter Chow

It is estimated that in 2020:

29,800 Canadians will be diagnosed with lung cancer. This represents 13% of all new cancer cases in 2020.

21,200 Canadians will die from lung cancer. This represents 25% of all cancer deaths in 2020.

15,000 men will be diagnosed with lung cancer and 11,000 will die from it.

14,800 women will be diagnosed with lung cancer and 10,200 will die from it.

On average, 81 Canadians will be diagnosed with lung cancer every day.

On average, 58 Canadians will die from lung cancer every day.

Lung cancer is the most commonly diagnosed cancer in Canada (excluding non-melanoma skin cancers). It is the leading cause of death from cancer for both men and women in Canada.

It is estimated that about 1 in 14 Canadian men will develop lung cancer during their lifetime and one in 16 will die from it.

About 1 in 15 Canadian women will develop lung cancer during their lifetime and one in 19 will die from it.

Lung cancer screening is a process that is used to detect the presence of lung cancer in otherwise healthy people at high risk for cancer.

Data shows that screening for lung cancer with low-dose computed tomography (LDCT) reduces the risk of dying from lung cancer in the high-risk population studied.

Despite good evidence to support screening, guideline implementation has been slower than optimal, often absent altogether.

On July 7, 2020, the U.S. Preventive Services Task Force, or USPSTF drafted a recommendation statement proposing:

Lung cancer screening using LDCT for people aged 50-80 years who are at high risk for developing lung cancer.

High risk was defined as people who have smoked at least 20 pack years over their lifetime and still smoke or former smokers who have quit within the last 15 years.

A pack-year calculates how much a person has smoked. One pack-year is equivalent to smoking an average of 20 cigarettes, or one pack, per day for a year.

In 2018, 15.8% of Canadians aged 12 and older (roughly 4.9 million people) smoked cigarettes either daily or occasionally, 18.6% for adult males and 13.0% for women.

Millions of Canadians fall into the category deemed high risk for lung cancer.

Why screen?

Lung cancer diagnosed without screening or ‘usual care’ has a poor prognosis, with a 5-year survival rate of 20%. However, early-stage non-small cell lung cancer has a much better prognosis.

So what is the evidence? There are currently 2 randomized controlled trials (RCT) that support lung cancer screening.

The NSLT (the National Lung Cancer Screening Research Trial Team) was conducted between 2002-2011.

It was a prospective, randomized trial.

NSLT compared LDCT screening to CXR (chest X-ray) screening for 3 annual screenings.

It enrolled 53,454 high-risk participants ages 55-74 years with current or former 30 pack-year smoking history or having quit within the last 15 years.

The endpoint of reduction in lung cancer mortality by 20% was met with a high level of statistical significance, and the study was stopped after a median follow-up of 6.5 years.

A positive screen was a nodule > 4 mm or other finding related to lung cancer.

The number of persons needed to screen to prevent 1 lung cancer mortality was 320 persons over 6.5 years.

The NELSON trial (Reduced Lung Cancer Mortality with Volume CT Screening in a Randomized Trial) was published in February 2020. This was the Dutch -Belgian lung cancer screening trial.

There were 13,195 participants, of whom 85% were male, ages 50 to 74 years.

They were broken into two groups randomized to usual care vs. screening LDCT at 1 year, 3 years, and 5.5 years.

At 10 years, the study met statistical significance of reducing lung cancer mortality by 25%.

The number needed to screen to prevent 1 lung cancer mortality was 130 persons over the screening period.

The NELSON trial provided empiric evidence for a younger starting age and lighter smoking history.

So, what are the harms of screening?

1)  False-positive nodules leading to unnecessary tests and invasive procedures.

The NSLT false-positive findings lead to invasive procedures like needle biopsies, bronchoscopies, thoracotomies in 1.7% of patients screened, with complications occurring in 0.1% persons screened.

2)  Overdiagnosis of cancer never destined to cause harm

Modelling predicts 6% of overdiagnosis if new guidelines are implemented.

3)  Radiation-induced cancers

The lifetime risk of cancer from radiation of 10 annual LDCT scan was 3 to 8 major cancers per 10,000 persons screened.

Modeling predicts the updated guidelines would result in an estimated 19 radiation-related cancer deaths per 100,000 persons (ages 45 to 90 years in the U.S.)

4)  Incidental findings other than pulmonary nodules

Common findings include coronary artery calcifications, aortic aneurysms, emphysema, and possible infections and inflammatory processes.

The benefits far outweigh the harms.

Shared decision making is important when doctors and patients discuss screening for lung cancer.

So, the question becomes, why aren’t we screening for lung cancer routinely, like we screen for breast cancer, cervical cancer, bowel cancer and prostate cancer?

 

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