The Burden of Lung Cancer
While lung cancer is estimated to account for just 13 percent of all new cases of cancer, it is both the most commonly diagnosed cancer and the leading cause of cancer death in Canada. In 2021, about 21,000 Canadians died from lung cancer. Worldwide, lung cancer is the second most common cancer. In 2020, more than 2.2 million new cases of lung cancer were diagnosed and an estimated 1.8 million people died as a result of the disease. Most people diagnosed with lung cancer live less than five years; the five-year net survival rate (based on data from 2015-2017) is only 22%.
Identifying Lung Cancer in Primary Care
Patients with lung cancer often experience symptoms prior to their diagnosis. Primary care providers can be alert for symptoms such as chronic cough, repeated respiratory infections, coughing up blood, shortness of breath, hoarseness, and chest pain, particularly among high-risk patients.
Another means of identifying potential lung cancer patients is risk factors. The major risk factor for lung cancer is smoking tobacco, which is responsible for about 72 percent of lung cancer cases in Canada. Another important risk factor is passive inhalation (second-hand smoke). Exposure to radon, asbestos, and outdoor air pollution all increase lung cancer risk. Occupational exposure to carcinogenic chemicals such as beryllium, cadmium and diesel engine exhaust may lead to lung cancer.
People working in some industries are exposed to multiple chemicals and are at higher risk for lung cancer. Some of these are rubber manufacturing, iron and steel founding, coal gasification and coke production, chimney sweeping, commercial painting, and roofing and paving.
Some diseases and medical treatments increase the risk of lung cancer. These include a history of lung disease (such as chronic obstructive pulmonary disease or tuberculosis), systemic lupus erythematosus, a weakened immune system (for example, due to HIV/AIDS or immunosuppressive therapy), or radiation treatment for cancer.
Screening for Lung Cancer
The Canadian Task Force on Preventive Health Care (CTFPHC) recommends that adults between 55 and 74 years of age who are at high risk for lung cancer be screened using low-dose computed tomography (LDCT) every year for three consecutive years. “High risk” comprises patients who are current smokers or who quit smoking during the previous 15 years and who have at least a 30 pack-year smoking history (pack-years are defined as the average number of cigarette packs smoked daily multiplied by the numbers of years the patient smoked).
In Canada, only two provinces (Ontario and British Columbia) have permanent screening programs for lung cancer. Both target high-risk asymptomatic patients, although the criteria differ somewhat from the CTFPHC recommendation. Pilot programs are underway in Alberta and Quebec to determine the utility of permanent programs.
Benefit of Screening
Two large clinical trials determined that screening high-risk individuals using low-dose computed tomography (LDCT) significantly reduces the risk of mortality due to lung cancer. The National Lung Screening Trial compared screening using LDCT with chest radiography in more than 53,000 patients. At five years, the relative risk of death due to lung cancer was 20 percent lower in the LDCT group. In the Dutch-Belgium NELSON trial, more than 15,000 patients (primarily male) who received either LDCT or no screening were followed up for a minimum of ten years. At ten-year follow-up, mortality was 24 percent lower in the LDCT group. These results were further supported by a 2022 Cochrane review, which found a mortality risk reduction of 21 percent with LDCT compared to no screening or screening using chest X-rays.
The Lifesaving Power of Early Detection
Early detection is the next frontier in the battle against lung cancer. Diagnosis earlier in the course of the disease could make a dramatic difference in the life expectancy of lung cancer patients. Currently nearly half of these patients are diagnosed at Stage IV and have an extremely low net five-year survival rate (4 percent). In contrast, patients diagnosed when their lung cancer is at Stage I have a 63 percent five-year survival rate. One expert estimates that early screening could allow up to 75 percent of lung cancers to be detected at an earlier, more treatable stage of the disease.
As patients’ first point of contact with the healthcare system, primary care providers have a key role to play in this shift. By identifying high-risk patients and referring them for screening, providers can improve patients’ odds of early detection and survival.
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