Lung cancer is classified into stages numbered 0 through IV, based on the size of the tumor, whether it has reached nearby lymph nodes, and whether it has spread to distant organs. The stage at diagnosis is one of the strongest predictors of outcome: the five-year survival rate is 65.5% when the cancer is still confined to the lung, 38.2% when it has reached nearby lymph nodes, and 10.5% when it has spread to distant parts of the body, according to federal cancer surveillance data.
How staging works depends on which type of lung cancer you have. Non-small cell lung cancer (NSCLC), which accounts for roughly 80 to 85% of cases, uses a detailed five-stage system. Small cell lung cancer (SCLC), a faster-growing type, is typically grouped into just two stages.
How Doctors Determine Your Stage
Staging relies on imaging and, sometimes, tissue sampling. After an initial diagnosis, you can expect some combination of CT scans, PET scans, MRIs, and bone scans. These tests map the tumor’s size, check whether cancer cells have reached lymph nodes, and look for signs of spread to organs like the brain, liver, bones, or adrenal glands. In some cases, a biopsy of a lymph node or suspicious spot is needed to confirm what imaging suggests.
The results feed into the TNM system: T describes the tumor’s size and whether it has grown into nearby structures, N describes lymph node involvement, and M indicates whether the cancer has metastasized. Combining these three factors places the cancer into an overall stage. An updated version of this classification system took effect in January 2025, refining how lymph node involvement and distant spread are categorized.
Non-Small Cell Lung Cancer: Stages 0 Through IV
Stage 0
At stage 0, abnormal cells are found only in the top layer of cells lining the airways. The cancer has not grown into deeper lung tissue, has not reached any lymph nodes, and has not spread. This is sometimes called carcinoma in situ, and it is rarely detected because it typically causes no symptoms.
Stage I
The tumor measures up to 4 cm across (roughly the size of a walnut or smaller) and remains within the lung. No lymph nodes are involved, and there is no distant spread. Stage I is the most treatable point on the spectrum. Surgery to remove the tumor or the affected section of lung is the standard approach for patients healthy enough for an operation. For those who can’t undergo surgery due to other health conditions, a focused form of radiation called stereotactic body radiotherapy (SBRT) is an effective alternative, typically delivered over about five sessions.
Stage II
Stage II covers two situations. The tumor may be larger, between 4 and 7 cm, without any lymph node involvement. Or it may be 3 cm or smaller but has reached lymph nodes within the lung itself or near the point where the airway branches into the lung. Surgery is still a primary option at this stage, often followed by chemotherapy or other treatments to reduce the chance of recurrence.
Stage III
This is where staging becomes more complex, and stage III is divided into sub-stages (IIIA, IIIB, and IIIC) that carry meaningfully different outlooks. The common thread is that the cancer has spread beyond the lung to nearby lymph nodes or structures but has not yet traveled to distant organs.
At one end, a stage IIIA tumor may be operable, with cancer in lymph nodes in the center of the chest (the mediastinum) on the same side as the tumor. At the other end, stage IIIC involves spread to lymph nodes on the opposite side of the chest or above the collarbone, or the tumor has grown directly into critical structures like the heart, trachea, or esophagus. There may also be multiple tumor nodules in different lobes of the same lung.
Treatment at stage III often combines radiation and chemotherapy, sometimes with immunotherapy afterward to help prevent the cancer from returning. Some stage IIIA patients are candidates for surgery as part of a broader treatment plan, but many stage III cancers are treated without an operation.
Stage IV
Stage IV means the cancer has spread beyond the chest. It is further split into IVA (spread to the other lung, or fluid containing cancer cells around the lung or heart) and IVB (spread to one or more distant organs). The most common sites where NSCLC spreads include bones, the brain and nervous system, the liver, the opposite lung, and the adrenal glands. The pattern varies somewhat by tumor type: adenocarcinoma, the most common subtype, tends to spread to bones and other parts of the respiratory system, while women and younger patients are more likely to develop brain metastases.
Stage IV lung cancer is not typically curable, but treatments have expanded significantly. The approach depends heavily on the cancer’s molecular profile. Tumors are tested for specific genetic mutations and protein markers that can be targeted with precision therapies. For example, cancers driven by certain mutations in genes like EGFR, ALK, or KRAS may respond to targeted drugs that block those specific growth signals. Cancers without a targetable mutation are often treated with immunotherapy, which helps the immune system recognize and attack cancer cells, sometimes combined with chemotherapy. These advances have meaningfully extended survival for many stage IV patients compared to a decade ago.
Small Cell Lung Cancer: Two Stages
Small cell lung cancer grows and spreads faster than NSCLC, so doctors use a simpler two-category system designed to guide treatment decisions quickly.
Limited stage means the cancer is confined to one side of the chest. It may involve one lung and lymph nodes on that same side, including nodes in the center of the chest. The defining feature is that the entire area of disease can be covered by a single radiation field. About one-third of SCLC patients are diagnosed at this stage, and treatment typically combines chemotherapy with radiation.
Extensive stage means the cancer has spread beyond what a single radiation field can cover, whether to the other lung, to fluid around the lungs, or to distant organs. SCLC is particularly likely to spread to the liver and the nervous system, with liver metastases found in about 35% and nervous system metastases in about 47% of patients with spread. Treatment centers on chemotherapy combined with immunotherapy.
Why Stage at Diagnosis Matters So Much
Lung cancer is often diagnosed at a later stage because the lungs have no pain receptors in their deeper tissues, and early tumors frequently cause no noticeable symptoms. By the time persistent cough, unexplained weight loss, or shortness of breath prompt a visit to a doctor, the cancer may have already spread beyond the lung.
The survival gap between early and late detection is stark. Patients diagnosed when the cancer is still localized have a five-year survival rate of 65.5%. Once it has reached regional lymph nodes, that drops to 38.2%. With distant metastasis, it falls to 10.5%. These numbers represent averages across all patients and don’t account for individual factors like age, overall health, or whether the cancer has a targetable mutation. Still, they underscore why low-dose CT screening for people at high risk (generally adults aged 50 to 80 with a significant smoking history) can catch the disease at its most treatable point.