What are the two main types of lung cancer?

The two main types of lung cancer are non-small cell lung cancer and small cell lung cancer. The names come from how the cells look under a microscope. Small cell tumors are made of small round cells with very little cytoplasm, the material inside a cell that surrounds its nucleus. Every other kind of lung cancer that starts in the lining tissue is grouped as non-small cell.

This split is not a technicality. The two types grow at different speeds, spread in different patterns, and are staged and treated in ways that share very little.

Non-small cell lung cancer

Non-small cell is by far the larger group. The National Cancer Institute divides it into three main forms. Adenocarcinoma is about 40% of lung cancers and starts in cells that make mucus. Squamous cell carcinoma is about 25% and starts in the flat cells that line the airways. Large cell carcinoma is about 10%. Rarer forms include adenosquamous carcinoma and carcinoid tumors.

Non-small cell lung cancer is staged with the AJCC TNM system. T describes the size and reach of the tumor, N describes lymph nodes, and M describes spread to distant organs. Those letters combine into stages I through IV. Early stages are often treated with surgery.

These tumors are also tested for gene changes that drugs can target. NCI lists EGFR, ALK, ROS1, BRAF, RET, NTRK, MET, KRAS, and HER2 among them. EGFR and ALK changes show up most often in adenocarcinoma in people who never smoked. KRAS and BRAF changes are more common in smokers. Finding one can open the door to a targeted drug, often a pill, instead of standard chemotherapy.

Small cell lung cancer

Small cell is about 15% of lung cancers. It is tied closely to tobacco use and is rare in people who never smoked.

It behaves very differently. It grows fast and has usually spread by the time it is found. Without treatment, median survival from diagnosis is only 2 to 4 months. NCI calls it the most aggressive course of any lung tumor.

Because of that speed, doctors often use a two-part system rather than stages I through IV. Limited stage means the cancer sits within one side of the chest and can fit inside a single radiation field. Extensive stage means it has gone past that, including to the other lung, the fluid around the lung, or distant organs.

Surgery is rarely the answer here. Small cell responds well at first to chemotherapy, usually a platinum drug paired with etoposide, and radiation to the chest is often added. Gene testing plays a much smaller role than it does in non-small cell disease.

How the type is decided

A pathologist sets the type by looking at tissue from a biopsy. A scan cannot do it. A CT or PET scan shows where a tumor sits and how far it has spread, but it cannot tell small cell from non-small cell.

Your pathology report should name the type and, for non-small cell, the subtype. Ask for a copy and check that both are there. If you have non-small cell lung cancer that has spread, ask whether biomarker testing was ordered and whether results are back, because they can change which treatment you are offered.

Quitting smoking still matters after diagnosis. NCI notes that people with limited-stage small cell disease should be urged to stop before combined chemotherapy and radiation, because continued smoking may shorten survival.