Understand lung cancer
Lung cancer is a type of cancer that starts in the lungs. Lung cancer is more likely to
develop in people who are 65 and older. There are two main types: non-small cell lung
cancer and small cell lung cancer.
The information on this page may help you gain a better understanding of your non-small cell lung cancer diagnosis and what’s happening to your body. This may help when making important decisions with your doctor.
What is non-small cell lung cancer (NSCLC)?

About 80% to 85% of people diagnosed with lung cancer have NSCLC. This makes it the most common type of lung cancer. NSCLC starts when healthy cells in the lung change and grow out of control, forming a mass called a tumor, lesion, or a nodule. A lung tumor can begin anywhere in the lung.
Types of non-small cell lung cancer
From the National Cancer Institute (NCI)
The information below is based on information originally published by the National Cancer Institute (NCI), the US government’s main agency for cancer research.
There are several types of non-small cell lung cancer.
Each type of non-small cell lung cancer has different kinds of cancer cells. The cancer cells of each type grow and spread in different ways. The types of non-small cell lung cancer are named for the kinds of cells found in the cancer and how the cells look under a microscope.
- Adenocarcinoma: Cancer that begins in the cells that line the alveoli and make substances such as mucus.
- Squamous cell carcinoma: Cancer that forms in the thin, flat cells lining the inside of the lungs. This is also called epidermoid carcinoma.
- Large cell carcinoma: Cancer that may begin in several types of large cells.
Stages of non-small cell lung cancer
NSCLC is described in 5 stages ranging from 0 to IV (4) with stage IV (4) being the most severe. Some stages can also be broken down further into substages (A, B, or C). The information below is meant to be a general guide. Use it to talk to your doctor about your specific stage of NSCLC.
Stage 0 non-small cell lung cancer
In stage 0, abnormal cells are found in the lining of the airways. These abnormal cells may become cancer and spread into nearby normal tissue.
Stage I (1) non-small cell lung cancer
In stage I, cancer has formed. Stage I is divided into stages IA and IB.
Stage II (2) non-small cell lung cancer
Stage II is divided into stages IIA and IIB.
Stage III (3) non-small cell lung cancer
Stage III is divided into stages IIIA, IIIB, and IIIC
Learn about a possible treatment option for certain patients with advanced non-small cell lung cancer and whose cancer also meets specific criteria.
Stage IV (4) non-small cell lung cancer
Stage IV is divided into stages IVA and IVB
Learn about a possible treatment option for certain patients with advanced non-small cell lung cancer and whose cancer also meets specific criteria.