The stage of a tumor refers to the extent to which a cancer has spread in the body. Staging involves both evaluation of a tumor’s size as well as the presence or absence of metastases in the lymph nodes or in other organs. Staging is important for determining how a particular tumor should be treated, since lung cancer therapies are geared toward specific tumor stages. Staging of a tumor is also critical in estimating the prognosis of a given patient, with higher-stage tumors generally having a worse prognosis than lower-stage tumors.

Doctors may use several tests to accurately stage a lung cancer, including laboratory (blood chemistry) tests, x-rays, CT scans, bone scans, and MRI scans. Abnormal blood chemistry tests may signal the presence of metastases in bone or liver, and radiological procedures can document the size of a tumor as well as possible spread to other organs.

NSCLC are assigned a stage from I to IV in order of severity.

In stage I, the cancer is confined to the lung.
In stages II and III, the cancer is confined to the chest (with larger and more invasive tumors classified as stage III).
Stage IV cancer has spread away from the chest to other parts of the body.

SCLC are staged using a two-tiered system:

Limited stage (LS) SCLC refers to cancer that is confined to its area of origin in the chest.
In extensive-stage (ES) SCLC, the cancer has spread beyond the chest to other parts of the body.