|IN THIS ARTICLE
— Lung Cancer Rates Among Non-Smokers Rising
— What Causes Lung Cancer in Non-Smokers: Why Are There So Many Cases?
— Are Women at Greater Risk than Men?
— How Is Cancer in Non-Smokers Different than in Those Who Smoke
Lung Cancer Rates Among Non-Smokers Rising
We typically think of lung cancer as a disease that mainly afflicts smokers. While it does have a much higher rate of occurrence in people who smoke, lung cancer can also affect people who have never smoked in their lives.
A National Cancer Center Singapore (NCCS) study in 2006 found that 32 percent of non-small-cell lung cancer (NSCLC) patients were never-smokers, which is defined as people who have smoked under 100 cigarettes in their lifetime. This number has increased to 48 percent over 10 years, according to another study done by the NCCS in 2018.
- From 2015–2019, there were 78,204 reported cases of cancer.
- The overall disease is found in men and women roughly equally, at 49 percent and 51 percent, respectively.
- Variations of cancer vary wildly: colo-rectum cancer is the most frequently found in men; breast cancer is the most common cancer in women.
- Lung cancer is the third most common form of cancer for men (13.7%) and women (7.7%).
Despite being lower in its frequency, lung cancer mortality rates are more prevalent. Patients with lung cancer have the highest mortality rate among cancer deaths for men (26.4%) and the third highest mortality rate for women (15.7%).
“If lung cancer unrelated to smoking is listed in its disease category, it will account to be roughly the sixth most deadly killer and causes of cancer deaths,” says Dr Harish Mithiran, managing thoracic surgeon of Neumark Lung and Chest Surgery Centre and senior consultant thoracic surgeon at Gleneagles Hospital, Singapore. He continues, “these global and local statistics uncover how vital it is to pay attention to lung cancer, whether we smoke or have never picked up a cigarette.”
Moreover, the risk of lung cancer differs by race or ethnicity. In the United States, approximately 10 percent of patients with lung cancer are never-smokers, while in Asia, more than 30 percent of patients with lung cancer are never-smokers and more than or almost 50 percent of lung cancers occur in women who are never-smokers.
Similar questions revolve around how sex affects the chances of lung cancer among never-smokers. Data suggest that lung cancer in non-smokers with lung cancer are usually women, younger, and have better survival outcomes than the regular rate of lung cancer in smokers. Similar to the rising frequency of lung cancer, the mortality rate is a question of maths. The data is skewed because historically, men had much higher rates of smoking, making for a higher mortality rate.
It remains true that women who have never smoked have a higher risk of lung cancer than men who do not smoke. The risk may be roughly equal for smokers across the sexes, but among non-smokers, it is slightly higher in women.
What Causes Lung Cancer in Non-Smokers: Why Are There So Many Cases?
Each patient is different and there may not be a single underlying cause when it comes to lung cancer, but rather a compilation of genetic, lifestyle and environmental factors that contribute to disease indication.
One of the strongest predictors of lung cancer is somatic abnormalities, or mutations in genes, that play pivotal roles in disease progression, especially in non-smokers. Genome studies of non-smoker cohorts have found that similar genes are involved in cell death, cell growth, and the metabolism of exogenous compounds, all affecting the chances of cancer.
Some research suggests that susceptibility alleles can be inherited, leading to an increased risk if the patient has a family history of lung cancer. However, it is also possible that because the family lives together, they may have all been exposed to similar air pollution or radon.
The World Health Organization estimates that a country’s 3 to 14 percent of all lung cancer cases are caused by radon exposure. This radioactive gas is colourless and odourless and stems from the natural breakdown of uranium in soil and rock. It can accumulate indoors, hence exposing people to unsafe levels of radon.
An NUS study investigated radon in Singapore and found that it was mostly under the levels of risk, though it would rise slightly in some locations with poor ventilation in the evenings. These low levels do not mean any risk.
Air pollution is the next major cause of lung cancer. A study in 2020 estimated that 14.1 percent of all lung cancer deaths worldwide are attributable to outdoor air pollution. In Singapore, that would be roughly 560 deaths from 2015–2019 caused by air pollution.
This study, however, does not pay particularly close attention to never-smokers. It did not isolate other risk factors, such as different smoking statuses or other factors that can lead to lung cancer death. Though we can be relatively certain that air pollution is a risk factor for lung cancer in non-smokers, we cannot put a number on that value yet.
Are Women at Greater Risk than Men?
This question has two possible answers, both corresponding to biology. It is likely that we can rule out radon exposure or air pollution as the cause, as we can assume men and women are exposed to similar amounts of radon and air pollution.
One main contributing factor to developing lung cancer in Asian females never-smokers are the driver gene mutations. A study conducted in China analysed specific driver gene mutations in Chinese never-smoker females with lung adenocarcinoma. The study discovered mutation rates of 76 percent, 5 percent, 4 percent, 2 percent, and 1 percent for EGFR, HER2, ALK, KRAS, and HER2, respectively, while only 12 percent of cases harboured no detected mutation. Fortunately, targeted therapy, which have a high response rate, has been developed for these mutations, helping to prolong the survival rates.
The other theory revolves around hormones. Research discovered that oestrogen accelerated lung cancer while testosterone inhibited it. Although limited to mice, other variables may be at play. Some studies found that oestrogen receptors in women are associated with lung adenocarcinoma patients and may be a sign of lung cancer in female non-smokers. However, these studies also did not differentiate between smokers and never-smokers, making it hard to understand the full importance of hormonal factors.
How Is Cancer in Non-Smokers Different than in Those Who Smoke
One of the most common types of lung cancer in non-smokers is adenocarcinoma. The cancerous tumour can start as glandular cells in the outer small airways of the lungs and advance to other parts of the body.
Adenocarcinoma is estimated in 40 percent of non-small cell lung cancer in non-smokers and smokers alike. It is different in shape than other types of lung cancer and typically shows as a hazy, diffused area versus spots or lumps in smokers. Furthermore, cancer in non-smokers tends to grow gradually and metastasize to other parts of the body. If detected early, the cancer can be removed successfully with surgery, with a significant reduction in rates of recurrence.
Most lung cancers are asymptomatic. However, some patients may have persistent dry coughs, cough with mucus or blood, feel breathless, or even experience chest pains.
What Can Be Done to Improve Lung Cancer Survival Rates
Over time, the stigma associated with lung cancer has grown because of its association with smoking. Among smokers and never-smokers alike, lung cancer stigma has shown to lead to increased anxiety and decreased quality of life following diagnosis. Your chances of survival are higher with early diagnosis. Allowing the stigma to control you will only increase the danger.
As best as we can see, it is hard to determine or isolate the different risk factors for lung cancer in never-smokers. But the problem remains: lung cancer is a real threat to smokers and non-smokers.
When lung cancer in those who do not smoke is diagnosed early, thoracic surgeons can oftentimes remove the affected lung tissue without complications, especially in non-smokers, as their lungs function more optimally than in smoker cohorts. It’s extremely important to treat any cancer as early as possible, especially when it’s locally confined before the disease metastasizes, carrying the cancerous cells to other parts of the body through the lymphatic system.
Lung cancer screening — typically through low-dose computed tomography (LDCT) scans — is one option, as, like with all cancers, early detection increases survival rates. By the time symptoms manifest in non-smokers, it is likely cancer has moved into a more advanced stage. Indeed, according to one study, most lung cancer cases among smokers were diagnosed at stages IA through IIIB, whereas 62 percent of cases among never-smokers had reached the most advanced stage by the time of diagnosis, Stage IV.
If you suspect something, it is important to get screened.
Patients who seek treatment at Neumark Lung and Chest Surgery Centre have access to a leading thoracic surgeon working with groundbreaking technologies and lung cancer research. We conduct consultations and early detection screening that can greatly increase your chances of getting ahead of any cancerous growth.