Adenocarcinoma of the lung is staged from I to IV based on three factors: the size of the tumor, whether cancer has reached nearby lymph nodes, and whether it has spread to distant organs. The stage at diagnosis is the single most important factor in determining treatment options and survival outlook. Most lung adenocarcinomas are staged using the same system applied to all non-small cell lung cancers, updated most recently in 2024.
How Staging Is Determined
Doctors use a combination of imaging and tissue sampling to assign a stage. A CT scan with contrast provides detailed anatomy of the chest, showing tumor size and whether nearby structures look involved. A PET/CT scan, which combines a CT with a metabolic tracer that highlights active cancer cells, is the preferred noninvasive method for staging. On CT, any lymph node with a short-axis diameter greater than 1 centimeter is flagged as potentially cancerous.
PET/CT is excellent at detecting whether cancer has spread to lymph nodes or distant sites, but surgical sampling of lymph nodes (a procedure called mediastinoscopy) remains the gold standard for confirming nodal involvement. If there’s suspicion of spread to the brain or liver, an MRI of those organs may follow. A biopsy of any suspicious area confirms the diagnosis and can reveal the genetic profile of the tumor, which increasingly shapes treatment decisions.
Stage I: Small Tumor, No Spread
Stage I lung adenocarcinoma means the tumor is no larger than 3 centimeters across and has not spread to any lymph nodes. This stage is subdivided into IA1, IA2, and IA3 based on small differences in tumor size. Stage IB includes tumors between 3 and 4 centimeters that still have no lymph node involvement.
Surgery to remove the tumor is the primary treatment. For larger Stage IB tumors (over 4 cm), additional therapy after surgery may be recommended. This can include chemotherapy, immunotherapy, or targeted therapy if the tumor carries certain genetic changes. For people who can’t undergo surgery, radiation therapy is an alternative. The five-year relative survival rate for localized lung cancer (which includes Stage I) is 65.5%, based on data from the National Cancer Institute’s SEER program covering 2016 through 2022.
Stage II: Larger Tumor or Limited Node Involvement
Stage IIA covers two scenarios: a tumor between 4 and 5 centimeters with no lymph node spread, or a smaller tumor (3 cm or less) that has reached nearby lymph nodes on the same side of the chest. Stage IIB involves slightly larger or more locally advanced combinations.
Surgery is still the cornerstone of treatment at this stage, but it’s commonly paired with additional therapy before or after the operation. Pre-surgery (neoadjuvant) chemotherapy, sometimes combined with immunotherapy, can shrink the tumor before it’s removed. Post-surgery (adjuvant) chemotherapy, immunotherapy, or targeted therapy helps eliminate any remaining cancer cells. If the tumor has specific genetic mutations, targeted drugs may be part of the plan. Radiation therapy serves as the main treatment for patients who aren’t surgical candidates.
Stage III: Regional Spread
Stage III means the cancer has spread more extensively to lymph nodes in the center of the chest or has grown into nearby structures, but has not traveled to distant organs. It’s divided into IIIA, IIIB, and IIIC based on the extent of lymph node involvement and how much the tumor has invaded surrounding tissue.
Stage IIIA tumors are sometimes still surgically removable. In those cases, surgery is combined with chemotherapy and often immunotherapy, given before and/or after the operation. When surgery isn’t feasible, the standard approach is chemotherapy delivered alongside radiation therapy. Stages IIIB and IIIC are generally not treated with surgery. Instead, the combination of chemotherapy and radiation, given either at the same time or one after the other, forms the backbone of treatment. The five-year relative survival rate for regional-stage lung cancer is 38.2%.
Stage IV: Distant Metastasis
Stage IV means cancer has spread beyond the chest. This stage is further divided based on where and how extensively the cancer has metastasized.
- M1a: Cancer has spread to the lining of the lung (pleura), the lining around the heart (pericardium), or fluid around the lung or heart contains cancer cells. It may also have spread to the opposite lung.
- M1b: A single area of cancer exists outside the chest, such as one spot in the brain, liver, or a single distant lymph node.
- M1c: Cancer has spread to multiple areas in one organ (for example, several spots in the bones) or to multiple organs.
Treatment at Stage IV focuses on controlling the disease and extending life rather than curing it. The approach depends heavily on the genetic profile of the tumor. Adenocarcinomas are more likely than other lung cancers to carry targetable genetic changes. If the tumor has mutations in genes like EGFR, ALK, ROS1, BRAF, RET, MET, or NTRK, specific drugs that block those pathways can be highly effective and are typically tried first. For tumors without a targetable mutation, treatment usually involves chemotherapy combined with immunotherapy or antibody-based drugs. If the cancer responds to initial treatment, maintenance therapy may continue to keep it in check. The five-year relative survival rate for distant-stage lung cancer is 10.5%, though outcomes vary widely depending on the specific sites of spread and how the tumor responds to targeted or immune-based treatments.
Clinical Stage vs. Pathological Stage
You may see two different stage labels in your medical records. The clinical stage is based on imaging and biopsies done before any surgery. The pathological stage comes after surgery, when a pathologist examines the removed tumor and lymph nodes under a microscope. The pathological stage is considered more accurate because it’s based on direct examination of tissue rather than imaging alone. In some cases, the stage changes after surgery, either up or down, once the full picture is clear.
Why Adenocarcinoma Staging Matters for Treatment
Adenocarcinoma is the most common type of lung cancer, accounting for roughly 40% of all cases. It tends to develop in the outer portions of the lung and is the type most frequently found in people who have never smoked. Because adenocarcinomas frequently carry specific genetic mutations, staging and molecular testing go hand in hand. A Stage IV adenocarcinoma with an EGFR mutation, for instance, may respond dramatically to targeted oral medications, while the same stage without that mutation would follow a different treatment path.
The stage at diagnosis sets the overall framework, but the tumor’s biology fills in the details. If you’ve recently been diagnosed, your oncologist will use both the stage and the results of molecular testing to build a treatment plan specific to your cancer.