Lung cancer falls into two major categories: non-small cell lung cancer (NSCLC), which accounts for the large majority of cases, and small cell lung cancer (SCLC), which makes up about 12%. Within those two groups are several subtypes that differ in where they start, how fast they grow, and where they tend to spread. Understanding the type matters because it directly shapes treatment options and outlook.
Non-Small Cell Lung Cancer
NSCLC is by far the more common form, and it includes three main subtypes: adenocarcinoma, squamous cell carcinoma, and large cell carcinoma. These subtypes behave differently, grow in different parts of the lung, and affect different populations.
Adenocarcinoma
Adenocarcinoma is the single most common type of lung cancer in the United States, accounting for 45% of all cases. It develops in the cells that line the lung’s tiny air sacs, the ones responsible for producing mucus and other substances. These tumors typically form in the outer portions of the lung, which sometimes means they grow for a while before causing noticeable symptoms like coughing or chest pain.
This is also the type most strongly associated with people who have never smoked. Among never-smokers diagnosed with lung cancer, 50% to 60% have adenocarcinoma. While smoking still raises the risk, adenocarcinoma is the subtype where other factors like radon exposure, air pollution, and genetic mutations play the largest relative role. Its incidence has held relatively steady over the past two decades, even as other subtypes have declined, which means adenocarcinoma now represents a growing share of total lung cancer diagnoses.
When adenocarcinoma spreads beyond the lungs, bone is the most common destination, affecting about 21.5% of patients with metastatic disease. Brain metastases occur in roughly 15% of cases.
Squamous Cell Carcinoma
Squamous cell carcinoma makes up about 21% of lung cancers. It forms in the thin, flat cells lining the inside of the airways and typically starts in the central part of the lungs, near the large bronchi. Because of this central location, it often causes symptoms earlier than adenocarcinoma, including persistent cough, coughing up blood, or airway obstruction.
This subtype has a stronger link to smoking than adenocarcinoma does. Among never-smokers with lung cancer, only 10% to 20% have squamous cell carcinoma. Its overall incidence has been declining since 2000, largely tracking the long-term drop in smoking rates. When squamous cell carcinoma does spread, bone is the most frequent distant site (about 11%), but the overall rate of metastasis to organs like the liver and brain is lower than with other subtypes. Brain metastases occur in roughly 6% of cases.
Large Cell Carcinoma
Large cell carcinoma is less common and can develop in any part of the lung. It tends to grow and spread more quickly than adenocarcinoma or squamous cell carcinoma, which can make it harder to treat when caught at a later stage. When it does metastasize, the brain is the most frequent single destination, affecting about 23.5% of patients with a single distant site of spread.
Small Cell Lung Cancer
Small cell lung cancer accounts for about 12% of all lung cancers and is almost always caused by smoking. It is the most aggressive form, growing and spreading significantly faster than any NSCLC subtype. By the time it’s diagnosed, it has often already spread beyond the lung.
Rather than the traditional stage I through IV system, doctors typically classify SCLC into two stages:
- Limited stage means the cancer is contained on one side of the chest. It may be in one lung and nearby lymph nodes (including those in the center of the chest or above the collarbone), but it’s still within a region that can be targeted with a single radiation field. This roughly corresponds to stages 1 through 3.
- Extensive stage means the cancer has spread beyond that single treatable area. It may have reached the other lung, distant lymph nodes, or other organs entirely. It can also mean fluid has built up between the layers of tissue surrounding the lungs or around the heart. This generally corresponds to stage 4.
SCLC’s spread pattern is distinct from other types. The liver is its most common metastatic site, affected in about 31.5% of cases. That rate is dramatically higher than for any NSCLC subtype (squamous cell carcinoma, by comparison, spreads to the liver only about 6% of the time). Bone metastases are also very common in SCLC (23.3%), and brain metastases affect roughly 17% of patients. The tendency to spread to distant lymph nodes is also higher in SCLC (10.6%) than in any other type.
Lung Neuroendocrine Tumors (Carcinoid Tumors)
A small fraction of lung cancers are neuroendocrine tumors, sometimes called carcinoid tumors. These form from hormone-producing cells in the lung and behave very differently from either NSCLC or SCLC.
- Low-grade (typical carcinoids) grow slowly and rarely spread beyond the lungs. They account for about 9 out of 10 lung neuroendocrine tumors and do not appear to be linked to smoking.
- Intermediate-grade (atypical carcinoids) grow faster and are more likely to spread. They are less common and occur more often in people who smoke.
Because of their slow growth, typical carcinoids are often found incidentally on imaging done for another reason. They carry a much better prognosis than other lung cancers.
How Stage Affects Survival
Across all types of lung cancer combined, the overall five-year survival rate is 29.5%. But that number varies enormously depending on how far the cancer has spread at diagnosis:
- Localized (still 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. About 21% of cases.
- Distant (spread to other organs): 10.5% five-year survival. Unfortunately, 51% of lung cancers are diagnosed at this stage.
The high proportion of late-stage diagnoses is the single biggest reason lung cancer survival rates remain lower than many other cancers. Type matters, but stage at diagnosis is the strongest predictor of outcome regardless of type.
Why Type Matters for Never-Smokers
Roughly 10% to 20% of lung cancers occur in people who have never smoked, and the distribution of types looks different in this group. Adenocarcinoma dominates, making up 50% to 60% of cases. Squamous cell carcinoma accounts for 10% to 20%, and small cell lung cancer is rare at just 6% to 8%. The rest are other or unclassified types.
This matters because lung cancer in never-smokers is increasingly recognized as a distinct category. These tumors are more likely to carry specific genetic mutations that can be targeted with newer therapies. If you’ve never smoked and receive a lung cancer diagnosis, knowing that it’s likely adenocarcinoma with potentially targetable mutations can open up treatment options that wouldn’t apply to smoking-related squamous cell or small cell cancers.