Lung cancer is often associated with smoking, but a notable number of individuals who have never smoked also develop this disease. In the United States, 10% to 20% of lung cancers occur in people who have never smoked or have smoked fewer than 100 cigarettes in their lifetime, amounting to 20,000 to 40,000 cases annually. Lung cancer in non-smokers is recognized as a distinct disease with different underlying causes and cellular characteristics compared to smoking-related lung cancer. While the diagnosis can be unexpected, there are specific risk factors and effective treatments for this population.
Survival Rates by Cancer Stage
A primary metric for understanding cancer outcomes is the 5-year relative survival rate. This rate compares people with a specific type and stage of cancer to the general population to determine the likelihood of being alive five years after diagnosis. These statistics are based on data from the Surveillance, Epidemiology, and End Results (SEER) database, which tracks cancer outcomes across the United States.
The most common type of lung cancer found in non-smokers is non-small cell lung cancer (NSCLC). Survival rates for NSCLC are categorized based on how far the cancer has spread. When the cancer is localized, meaning it is confined to the lung, the 5-year relative survival rate is approximately 65%.
If the cancer has spread to nearby lymph nodes or structures, it is classified as regional, and the 5-year relative survival rate is about 37%. When the cancer has metastasized to distant parts of the body such as the brain, bones, or liver, it is categorized as distant-stage cancer. In these cases, the 5-year relative survival rate drops to 9%. These are general statistics, and an individual’s prognosis can be influenced by many other factors.
Prognostic Factors in Non-Smokers
Several factors influence the prognosis for a non-smoker diagnosed with lung cancer. Adenocarcinoma is the most prevalent form, accounting for about 50% to 60% of cases. This type of cancer develops in the cells that line the lungs’ tiny air sacs and produce mucus. The prognosis for non-smokers with lung cancer is often better than for smokers, with one study showing a median survival of 15.13 months for non-smokers compared to 10.17 months for smokers.
The stage at which the cancer is diagnosed is another major determinant of the outcome. Unfortunately, because lung cancer is often not suspected in non-smokers, the diagnosis may occur at a more advanced stage when symptoms have already appeared. Symptoms can include a persistent cough, chest pain, wheezing, and recurring lung infections. One study found that 62% of non-smokers were diagnosed at stage IV, the most advanced stage.
A defining aspect of lung cancer in non-smokers is the presence of specific genetic mutations within the tumor cells. These changes in the DNA of the cancer cells drive their growth. The presence of biomarkers, such as mutations in the epidermal growth factor receptor (EGFR) gene and rearrangements in the anaplastic lymphoma kinase (ALK) and ROS1 genes, is a powerful prognostic factor because they can be targeted with specific medications.
Causes and Risk Factors for Lung Cancer in Non-Smokers
While smoking is the leading cause of lung cancer, several other factors can lead to the disease in individuals who have never smoked.
- Radon gas exposure is a leading risk factor. This naturally occurring radioactive gas can seep into homes from the ground and accounts for an estimated 2,900 lung cancer deaths in non-smokers each year in the U.S.
- Secondhand smoke is an established cause, contributing to about 7,300 lung cancer cases annually. One analysis found that women who never smoked but were married to smokers had a 27% higher risk of developing lung cancer.
- Workplace exposures to carcinogens like asbestos, diesel exhaust, chromium, and arsenic also play a role. People in certain occupations may have prolonged exposure to these agents.
- Long-term exposure to high levels of outdoor air pollution has also been linked to DNA damage that can lead to tumor growth.
- A person’s genetic makeup can influence their susceptibility. A family history of lung cancer, especially in a close relative diagnosed at a young age, can indicate a higher risk.
Somatic mutations, which are changes in genes that occur during a person’s lifetime due to environmental exposures, can also drive the development of lung cancer.
Impact of Modern Treatments on Survival
Treatment advances, driven by a better molecular understanding of the disease, have improved survival rates for non-smokers with lung cancer. The discovery of specific genetic mutations has led to the development of highly effective targeted therapies. These treatments are designed to attack cancer cells that have particular mutations, such as those in the EGFR, ALK, or ROS1 genes.
Targeted therapies, often oral pills, work by blocking the signals that cause cancer cells to grow and divide. This approach is more effective and has fewer severe side effects than traditional chemotherapy because it specifically targets cancer cells while sparing most healthy cells. For many with advanced lung cancer, targeted therapies can turn the disease into a manageable condition, extending both the length and quality of life.
Another revolutionary treatment is immunotherapy, which harnesses the body’s own immune system to destroy cancer cells. Medicines like pembrolizumab and atezolizumab stimulate the immune system to more effectively fight the cancer. While studies have shown immunotherapy may be more effective in smokers, it remains a valuable option for some non-smokers, often used in combination with other treatments.