Lung cancer falls into two main categories: non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC). NSCLC accounts for roughly 85% of all lung cancers, while SCLC makes up the remaining 15%. Within those two groups are several distinct subtypes, each with different behavior, outlook, and treatment approach.
Non-Small Cell Lung Cancer
NSCLC is an umbrella term covering three major subtypes: adenocarcinoma, squamous cell carcinoma, and large cell carcinoma. These cancers grow and spread more slowly than small cell lung cancer, and the overall five-year survival rate across all stages is 32%. When caught early and still confined to the lung, that number jumps to 67%.
Adenocarcinoma
Adenocarcinoma is the single most common form of lung cancer, representing about 40% of all cases. It starts in the cells that line the small air sacs deep in the lungs, so tumors tend to form in the outer, peripheral areas rather than near the central airways. This matters because peripheral tumors can grow for a while before causing noticeable symptoms like coughing or chest pain.
Adenocarcinoma is also the type most closely linked to never-smokers. Among people who develop lung cancer without any history of tobacco use, 93% have adenocarcinoma. The reasons aren’t fully understood, but genetic mutations play a large role. About 20% of adenocarcinomas carry specific gene changes (in EGFR, ALK, or ROS1) that make the cancer vulnerable to targeted therapy pills rather than traditional chemotherapy. Another roughly 30% produce high levels of a protein called PD-L1, which makes them candidates for immunotherapy. The remaining 50% lack these markers and are typically treated with standard chemotherapy combinations.
Squamous Cell Carcinoma
Squamous cell carcinoma accounts for about 30% of lung cancers. Unlike adenocarcinoma, these tumors usually develop in the large, central airways of the lung and are strongly tied to tobacco smoking. The cells involved are flat, scale-like cells that line the bronchi.
Because these tumors sit near the main airways, they often cause symptoms earlier, including a persistent cough, coughing up blood, or recurrent pneumonia when a tumor partially blocks an airway. Squamous cell carcinomas frequently carry mutations in the p53 gene, a tumor suppressor that normally keeps cell growth in check. Treatment options overlap with other NSCLC types but are less likely to involve the targeted therapies used for adenocarcinoma, since the treatable gene rearrangements found in adenocarcinoma are rare here.
Large Cell Carcinoma
Large cell carcinoma is the least common of the three major NSCLC subtypes. It can appear anywhere in the lung and tends to grow faster than adenocarcinoma or squamous cell carcinoma. Under a microscope, the cells look large and undifferentiated, meaning they don’t resemble the normal lung tissue they came from. This lack of differentiation is part of what makes large cell carcinoma more aggressive.
Small Cell Lung Cancer
Small cell lung cancer is the more dangerous of the two main categories. It grows rapidly, divides at an extremely high rate, and spreads early. By the time most people are diagnosed, the cancer has already moved beyond the lungs to distant organs like the brain, liver, or bones. The five-year survival rate across all stages is just 9%, compared to 32% for NSCLC. Even when caught while still localized, the five-year survival rate is 34%.
SCLC is found almost exclusively in heavy smokers. The cancer originates from neuroendocrine cells in the lung and is classified as a high-grade neuroendocrine tumor. It initially responds well to chemotherapy and radiation, often shrinking dramatically. But in most patients, the cancer comes back in a form that resists further treatment. Surgery is only an option for a small number of people whose disease is caught very early and remains confined to one area.
Doctors typically stage SCLC differently from NSCLC, using a simpler two-stage system: limited stage (cancer is on one side of the chest) and extensive stage (cancer has spread more widely). Most patients are diagnosed at the extensive stage.
Carcinoid Tumors
Lung carcinoid tumors are a much rarer form of lung cancer, accounting for about 2% of all lung tumors. Like SCLC, they arise from neuroendocrine cells, but they behave very differently. Typical carcinoids grow slowly, rarely spread, and have a relatively good prognosis. Atypical carcinoids, which make up only 0.2% of lung tumors, are somewhat more aggressive but still far less dangerous than SCLC.
The distinction between the two comes down to how fast the cells are dividing and whether dead tissue is visible in the tumor. Typical carcinoids show minimal cell division and no internal tissue death. Atypical carcinoids show more active division and may contain areas of dead tissue. Both types are more often treated with surgery than with chemotherapy.
Pancoast Tumors
Pancoast tumors aren’t a separate cell type. They’re defined by location: the very top of the lung, at the apex near the first rib. Any type of NSCLC can form here, but the location creates a unique set of symptoms. As the tumor grows, it presses into the bundle of nerves that runs from the spine into the arm (the brachial plexus) and into nearby nerve structures in the neck.
The result is a distinctive pattern: severe pain in the shoulder and arm, numbness or tingling in the hand (especially the ring finger, pinky, and inner forearm), and weakness in the small muscles of the hand that control grip. If the tumor invades a particular nerve chain in the neck, it can cause a drooping eyelid, a smaller pupil, and loss of sweating on that side of the face. This combination is called Horner syndrome. Because these symptoms mimic orthopedic or nerve problems, Pancoast tumors are sometimes misdiagnosed for months before the true cause is found.
Lung Cancer in Never-Smokers
While smoking remains the leading cause of lung cancer overall, the disease does occur in people who have never smoked. Lung cancer in never-smokers is almost exclusively NSCLC, with adenocarcinoma dominating at 93% of cases. These cancers are more likely to carry the specific gene mutations that respond to targeted therapies, which means treatment options can actually be broader for some never-smokers than for smokers with squamous cell or small cell disease.
The causes in never-smokers aren’t fully explained, but known risk factors include radon exposure, secondhand smoke, air pollution, and inherited genetic susceptibility. Because these patients often lack the classic risk profile, their cancers may be caught later, making awareness of adenocarcinoma’s existence outside of smoking particularly important.
Why the Type Matters for Treatment
Identifying the exact type of lung cancer is one of the first and most consequential steps after diagnosis. A biopsy sample is examined under a microscope to determine whether it’s NSCLC or SCLC, and if it’s NSCLC, which subtype. For adenocarcinomas, further molecular testing checks for treatable gene mutations and protein markers. This testing can take one to two weeks but directly determines whether you’re a candidate for targeted therapy, immunotherapy, or chemotherapy.
The practical difference is significant. A patient with an EGFR-mutated adenocarcinoma may take a daily pill with relatively manageable side effects, while someone with small cell lung cancer typically receives intensive chemotherapy cycles in an infusion center. Two people with “lung cancer” can have fundamentally different diseases, different treatment experiences, and different outlooks based entirely on which type of cell went wrong.