The four main types of lung cancer are adenocarcinoma, squamous cell carcinoma, large cell carcinoma, and small cell carcinoma. The first three fall under a broader category called non-small cell lung cancer (NSCLC), which accounts for about 77% of all lung cancers. Small cell lung cancer (SCLC) makes up roughly 13%, with the remaining cases being rarer tumors like carcinoids. Each type behaves differently, grows in different parts of the lung, and responds to different treatments.
How Lung Cancer Is Classified
When a tissue sample is taken from a lung tumor, a pathologist examines the cells under a microscope and runs specialized staining tests to determine the cancer’s type. Two key markers do most of the heavy lifting: one protein identifies adenocarcinoma, while a different protein flags squamous cell carcinoma. If neither marker lights up and the cells don’t resemble small cell carcinoma either, the diagnosis lands on large cell carcinoma, which is essentially a diagnosis of exclusion.
Getting the type right matters because it directly shapes treatment. Certain targeted therapies only work on cancers with specific genetic mutations, and those mutations cluster in particular types. Immunotherapy, chemotherapy, surgery, and radiation are all used across lung cancers, but the combinations and sequencing depend heavily on which of the four types you’re dealing with.
Adenocarcinoma: The Most Common Type
Adenocarcinoma is the single most common form of lung cancer. It develops in the cells that line the small air sacs deep in the lungs, where gas exchange happens. This type is strongly linked to smoking, but it’s also the subtype most frequently found in people who have never smoked. Over 65% of lung cancer patients with no smoking history are diagnosed with adenocarcinoma.
One reason adenocarcinoma gets so much attention in treatment research is that it frequently carries targetable genetic mutations. Changes in genes called EGFR, ALK, and KRAS are especially common. EGFR mutations appear at higher rates in Asian women compared to women of other ethnic backgrounds. These mutations act like on-switches that tell cancer cells to keep growing, and drugs designed to block them can be remarkably effective. If you’re diagnosed with adenocarcinoma, your oncologist will almost certainly order molecular testing to look for these mutations before deciding on a treatment plan.
Squamous Cell Carcinoma
Squamous cell carcinoma develops in the flat cells lining the large central airways of the lungs, the bronchi. Because of this central location, it often causes symptoms earlier than adenocarcinoma: a persistent cough, coughing up blood, or recurring lung infections from a partially blocked airway.
This type has the strongest association with tobacco smoke. The link makes biological sense. Inhaled smoke flows directly through the large central bronchi first, and the constant irritation transforms normal airway lining cells into cancerous ones over time. Squamous cell carcinoma carries targetable mutations less often than adenocarcinoma, so treatment more commonly involves combinations of chemotherapy, immunotherapy, and radiation. Surgery is an option when the cancer is caught at an earlier stage.
Large Cell Carcinoma
Large cell carcinoma is the least common of the four main types. Under the microscope, its cells appear large and abnormal but lack the defining features of adenocarcinoma, squamous cell carcinoma, or small cell carcinoma. Pathologists can only make this diagnosis on a fully removed tumor, not from a small biopsy, because they need to rule out all other types across the entire specimen.
This “none of the above” nature makes large cell carcinoma poorly differentiated, meaning the cells have lost the specialized characteristics that would identify their origin. In practical terms, this often translates to aggressive behavior. Treatment typically follows the general approach for non-small cell lung cancer: surgery when possible, combined with chemotherapy and potentially immunotherapy depending on the stage and the tumor’s specific characteristics.
Small Cell Lung Cancer
Small cell lung cancer is biologically distinct from the other three types. Its cells are small, tightly packed, and divide rapidly. The National Cancer Institute describes it as a cancer that can grow and spread quickly, often reaching other parts of the body early in the disease process. The vast majority of small cell lung cancer cases occur in people with a significant smoking history.
Because it spreads so early, small cell lung cancer uses a simpler two-stage system instead of the standard four-stage approach. Limited-stage means the cancer is still confined to one lung and possibly nearby lymph nodes. Extensive-stage means it has spread beyond that, to the other lung or distant organs. Most people are diagnosed at the extensive stage.
Chemotherapy is the primary treatment for nearly all small cell lung cancer. It’s often paired with immunotherapy, particularly in extensive-stage disease. Surgery plays a role only in the rare cases caught very early. The cancer typically responds well to initial chemotherapy, but recurrence rates are high, which is why small cell lung cancer carries a more serious prognosis than most non-small cell types.
How Treatment Differs Across Types
For non-small cell lung cancers (adenocarcinoma, squamous cell, and large cell), surgery is a cornerstone of treatment at stages 1, 2, and sometimes 3. Chemotherapy may be given before surgery to shrink the tumor, or after surgery to catch any remaining cells. Immunotherapy has become a standard addition at many stages, either alongside chemotherapy or on its own. When a tumor can’t be safely removed, chemotherapy combined with radiation is the typical path, often followed by immunotherapy.
For small cell lung cancer, the approach leans heavily on chemotherapy from the start, usually combined with immunotherapy for extensive-stage disease. Radiation to the chest often follows, and many patients also receive preventive radiation to the brain to reduce the risk of the cancer spreading there.
Across all types, the overall five-year survival rate for lung and bronchus cancers is 29.5%, based on data from 2016 to 2022. That number has been climbing steadily thanks to immunotherapy, targeted drugs, and earlier detection through screening. Survival varies significantly by type and stage, with early-stage non-small cell cancers having much better outcomes than extensive-stage small cell disease.
Rarer Types Worth Knowing About
Beyond the four main types, lung carcinoid tumors deserve a brief mention. These arise from neuroendocrine cells in the lungs and behave very differently from typical lung cancers. The most common form, called typical carcinoids, grows slowly and rarely spreads. Atypical carcinoids grow somewhat faster and carry a higher risk of spreading, but both types are far less aggressive than the four main lung cancers. Traditional chemotherapy is rarely used for carcinoids because it targets fast-growing cells, and carcinoids simply don’t grow fast enough for it to be effective.