The link is undeniable: when we consider lung cancer, our minds immediately turn to smoking. Smoking remains the principal risk factor for developing this type of tumour.
However, the reality is that between 10% and 20% of cases occur in people who have never smoked. In these instances, the risk factors are quite different and, occasionally, far more challenging to identify.
"I believe the first point to stress - and something we've reiterated countless times over the decades - is that the leading cause linked to the development of lung cancer (among other forms of cancer) is tobacco," explains Dr Fabio Franco, a medical oncologist and Head of the Multidisciplinary Thoracic Tumour Unit at MD Anderson Cancer Centre Madrid-Hospiten.
"In Western nations, over 80% of these tumours are a direct result of smoking."
Want to know more? Lung cancer expert Dr Franco is helping clear up any confusion, answering some of the most common questions.
What risk factors can lead to lung cancer in non-smokers?
"There is a cohort of patients, typically around 10-20%, who develop lung cancer without any history of smoking, or when smoking has been extremely limited. In these particular cases, molecular testing is crucial, as the origin of these tumours is often explained by specific genetic alterations, such as mutations in the EGFR gene or fusions in genes like ALK and ROS1, to name a few.
"Another established cause of lung cancer in never-smokers is sustained exposure to radon gas.This gas is a natural source of radiation and can account for nearly 50% of the natural radiation a person absorbs throughout their lifetime."
"There is a cohort of patients, typically around 10-20%, who develop lung cancer without any history of smoking, or when smoking has been extremely limited"
Are lung cancer cases among non-smokers becoming more frequent?
"When we discuss lung cancer in people who have never smoked, it isn't clear that the frequency is increasing. What has changed is the diagnostic approach and our enhanced ability to identify a clear cause by analysing gene sequencing studies that can explain the genesis, clinical features and progression of the disease."
What risk factors can lead to lung cancer in non-smokers?
"As previously mentioned, there are several conditions that can generate this type of cancer, and all are determined by a degree of genetic predisposition. Coupled with this are environmental exposures, such as prolonged exposure to radon (a form of natural radiation), other types of ionising radiation, and agents like asbestos, silica, and arsenic, amongst others.
"Current genomic studies now enable us to identify specific alterations in genes in a large percentage of these patients. These alterations are linked to the development of the disease and cause it to behave in a biologically distinct manner. The most frequent alterations include mutations in the gene known as EGFR or fusions in genes such as ALK, ROS1, NTKR, and so on."
"If there's one thing we need to emphasise, it's to abstain completely from tobacco and its derivatives - including vaping"
Are the symptoms similar in smokers and non-smokers?
"Generally speaking, the symptoms are similar across both populations. This is because the symptoms are caused by damage or compromise to the [body], no matter what caused the tumour. For example, a cough or shortness of breath might be due to the direct involvement or compression of the bronchi or the pleura - a kind of damage we see in both groups of patients."
Is there often a delay in diagnosis for non-smoking patients, because the obvious risk factor - smoking - is missing?
"A lung cancer diagnosis is prompted by a symptom followed by an exam, which then leads to the patient undergoing diagnostic tests. So the diagnosis shouldn't necessarily be delayed. One difference, though, is that the diagnosis might be discovered incidentally for patients involved in screening programmes or those being monitored for other, non-cancerous, pulmonary conditions.
The origin of lung cancer in non-smokers is often explained by specific genetic mutations or sustained exposure to radon gas
"It's important to remember that diagnosis is going to require a number of tests [for both smokers and non-smokers]. These tests will help define both the type and the extent of the disease, which will in turn help to map out the therapeutic approach. This entire process, particularly analysing the tumour's molecular profile, takes time."
What precautions and lifestyle habits should we consider to prevent lung cancer?
"If there's one thing we need to emphasise, it's to abstain completely from tobacco and its derivatives, including vaping. That, along with making sure to get enough regular physical activity and exercise."
Once a lung cancer diagnosis is confirmed, what treatment options are available?
"With lung cancer, precision oncology has been fully implemented, and new horizons are opening every day. The treatment options are extremely wide-ranging but will depend on the type of tumour diagnosed, its progression and its molecular characteristics.
"Your doctor may consider surgical treatments, radiotherapy, chemotherapy, immunotherapy and targeted therapies against specific genomic alterations.
"These treatments can be used individually, sequentially or combined, depending on each particular case."