Lung cancer is a disease in which cells in the lungs grow uncontrollably, forming tumors that can interfere with breathing and spread to other parts of the body. It is the leading cause of cancer death in the United States, and cigarette smoking is linked to 80% to 90% of lung cancer deaths. But lung cancer also affects people who have never smoked, driven by factors like radon gas exposure and genetic mutations.
How Lung Cancer Develops
Lung cancer starts when DNA inside lung cells becomes damaged. Healthy cells grow and divide in an orderly way, but mutations in certain genes disrupt that process. Some of the most common mutations found in lung tumors occur in genes called EGFR, KRAS, and TP53. When EGFR or KRAS is mutated, the affected protein gets stuck in the “on” position, sending constant signals for the cell to multiply. Over time, this unchecked growth forms a mass of abnormal tissue.
These mutations can be caused by carcinogens in tobacco smoke, but they also arise from environmental exposures or, in some cases, without a clearly identifiable trigger. Once a tumor establishes itself in the lung, it can invade nearby tissue and eventually release cells into the bloodstream or lymphatic system, allowing cancer to take root in distant organs like the bones, brain, or liver.
Types of Lung Cancer
Not all lung cancers behave the same way. According to CDC data from 2022, the most common subtypes in the United States break down like this:
- Adenocarcinoma (45% of cases): The most common form overall, and the type most frequently diagnosed in people who have never smoked. It typically starts in the outer regions of the lung.
- Squamous cell carcinoma (21%): Usually found in the central airways of the lung and strongly linked to smoking history.
- Small cell carcinoma (12%): The most aggressive form. It tends to grow quickly and spread to other parts of the body before it causes noticeable symptoms.
Adenocarcinoma and squamous cell carcinoma both fall under the broader category of non-small cell lung cancer, which accounts for the large majority of diagnoses. The distinction matters because small cell and non-small cell cancers are treated differently and have very different timelines.
Symptoms to Recognize
Lung cancer typically does not cause symptoms in its early stages, which is one reason it is so often caught late. When symptoms do appear, the most common ones involve the chest and airways: a new cough that does not go away, chest pain, hoarseness, shortness of breath, and wheezing.
Once the cancer has spread beyond the lungs, symptoms reflect where it has traveled. Bone pain, persistent headaches, unexplained weight loss, and loss of appetite can all signal advanced disease. None of these symptoms are unique to lung cancer, which is part of what makes early detection so difficult without screening.
Risk Factors Beyond Smoking
Smoking is by far the dominant risk factor, but it is not the only one. Radon, a naturally occurring radioactive gas that seeps into homes through cracks in foundations, is the second leading cause of lung cancer overall and the number one cause among nonsmokers. The EPA estimates radon is responsible for about 21,000 lung cancer deaths per year in the U.S., roughly 2,900 of them in people who have never smoked.
The combination of smoking and radon is especially dangerous. A smoker exposed to a radon level of 1.3 pCi/L (a common indoor concentration) has about a 20 in 1,000 chance of dying from lung cancer, compared to 2 in 1,000 for a nonsmoker at the same exposure level. Other known risk factors include exposure to asbestos, air pollution, and a family history of lung cancer.
How Lung Cancer Is Staged
Staging describes how far the cancer has progressed and is the single biggest factor in determining treatment options and outlook. Doctors use the TNM system, which evaluates three things: the size of the primary tumor (T), whether cancer has reached nearby lymph nodes (N), and whether it has metastasized to distant organs (M). These three factors combine to assign an overall stage from I through IV.
Stage I and II cancers are smaller and confined to the lung or its immediate surroundings. Stage III means the cancer has spread to lymph nodes in the chest. Stage IV means it has reached distant parts of the body, such as the bones, brain, or liver. More than half of all lung cancers (51%) are already at the distant stage when first diagnosed, which is a major reason the disease carries such high mortality.
Survival Rates by Stage
The stage at diagnosis dramatically affects outcomes. Five-year relative survival rates from the National Cancer Institute’s SEER database (2016 to 2022 data) illustrate the gap clearly:
- Localized (confined to the lung): 65.5% five-year survival. About 24% of cases are caught at this stage.
- Regional (spread to nearby lymph nodes): 38.2% five-year survival. This accounts for 21% of cases.
- Distant (metastasized): 10.5% five-year survival. This is the stage at which 51% of patients are diagnosed.
These numbers highlight why early detection matters so much. A person diagnosed when the cancer is still localized has more than six times the survival rate of someone diagnosed after it has spread to distant organs.
Who Should Get Screened
The U.S. Preventive Services Task Force recommends annual screening with a low-dose CT scan for adults aged 50 to 80 who have a 20 pack-year smoking history and either currently smoke or quit within the past 15 years. A pack-year equals smoking one pack (20 cigarettes) per day for one year, so someone who smoked a pack a day for 20 years, or two packs a day for 10 years, meets the threshold.
Screening stops once a person has been smoke-free for 15 years or develops a health condition that would make treatment impractical. Low-dose CT is the only screening method currently recommended. Standard chest X-rays are not sensitive enough to catch lung cancer at an early, treatable stage.
How Lung Cancer Is Treated
Treatment depends on the type and stage of the cancer, and increasingly on the specific genetic mutations driving the tumor. For early-stage non-small cell lung cancer, surgery to remove the tumor or the affected section of lung is the primary approach, sometimes followed by additional therapy to reduce the risk of recurrence.
For advanced disease, the treatment landscape has shifted significantly. Traditional chemotherapy works by killing rapidly dividing cells throughout the body, which damages healthy tissue along with cancer cells and causes well-known side effects like nausea, fatigue, and hair loss. Newer targeted therapies take a more precise approach. If a tumor carries a specific mutation, like an EGFR or ALK alteration, drugs can be designed to block the exact protein driving that cancer’s growth. Because these therapies are selective, they tend to cause fewer side effects than conventional chemotherapy.
Doctors now routinely test lung tumors for a panel of genetic mutations to determine whether targeted treatment is an option. The most commonly tested mutations include EGFR, ALK, ROS1, BRAF, KRAS, MET, and RET. For patients whose tumors carry one of these markers, targeted drugs can sometimes control the disease for months or years, even in advanced stages. Immunotherapy, which helps the body’s own immune system recognize and attack cancer cells, is another option that has improved outcomes for many patients whose tumors are not candidates for targeted drugs.
Small cell lung cancer, because of its tendency to spread early and aggressively, is usually treated with a combination of chemotherapy and radiation rather than surgery. It often responds well to initial treatment but has a high rate of recurrence.