What Is Lung Cancer?

Lung cancer is a disease in which abnormal cells grow in your lungs and form large masses known as tumors. There are several types of lung cancer based on the microscopic appearance and molecular characteristics of the tumor. Based on size, location in and outside of the lungs, the stage of the cancer is determined.  Assessing the molecular structure of the tumor might have significant impact on the choice of therapy and outcome.

Lung cancer is diagnosed in about 230.000 patients annually in the US, and causes more deaths in the United States than any other cancer. It is increasingly more common in women and younger patients with no or light smoking history. Although lung cancer historically has been difficult to treat, over the last decade there has been tremendous progress in treatment advances, making this an exciting and hopeful time for patients.

Types of Lung Cancer

There are two main types of lung cancer: non-small cell lung cancer small cell lung cancer.

Non-small cell lung cancers (NSCLC)
Most lung cancer patients (about 85 percent) have non-small cell cancers. There are six types of non-small cell cancers:

  • Squamous cell carcinoma: This condition is generally caused by smoking. These cells are typically located in the central air passageways.
  • Adenocarcinoma: This type of cancer can affect anyone regardless of smoking. It is particularly common among younger patients and women. 
  • Adenocarcinoma in situ: This cancer sometimes resembles a lung infection.
  • Adenosquamous carcinoma: This is a rare mixed subtype and aggressive disease.
  • Large cell carcinoma: This condition can appear anywhere in the lungs and tends to grow quickly.
  • Undifferentiated carcinoma: These cancer cells are immature and tend to be malignant. 

Small cell lung cancers (SCLC) and others:
The three types of small cell lung cancer are:

  • Small cell carcinoma: Often caused by smoking, this condition responds well to treatment.
  • Mixed small cell/large cell carcinoma: Usually called combined small cell carcinoma, this condition has cells that have characteristics of both small and non-small cell lung cancers.
  • Combined small cell carcinoma: This condition—small cell lung cancer combined with squamous and/or secreting cells—has several phases.
  • Large cell neuroendocrine carcinomas: A tumor, which based on molecular characteristics resembles small cell lung cancer.


Part of the diagnostic process involves determining the stage of lung cancer, which is important for treatment decisions. The stage of your cancer reflects where the cancer cells are in your lungs, how large the tumor is, and if the cancer has spread to more than one spot.

Both letters and numbers describe the cancer. The letters are:

  • T: This denotes the tumor’s size and where it’s located in your lungs or body.
  • N: This means node involvement. This tells us if the cancer has spread to the lymph nodes near your lungs.
  • M: This stands for metastasis, which means that cancer has spread. Lung cancer can spread from one of your lungs to the other. It can also metastasize to other parts of your body including the liver, bones, brain, kidneys, and adrenal glands.

The numbers are:

  • Occult stage: Also called hidden cancer, this means we can’t see your tumor on imaging screens or in a biopsy. We can only see it in the mucus you cough up.
  • Stage 0: Your tumor is very small. It hasn’t spread into your deeper lung tissues or outside your lungs.
  • Stage I: You have cancer in your lung tissues but not your lymph nodes.
  • Stage II: Cancer cells may have spread to the lymph nodes near your lungs.
  • Stage III: Cancer cells have spread into your lymph nodes and the middle of your chest.
  • Stage IV: You have cancer in several parts of your body.

Stages 1- 3 are usually considered early lung cancer and stage 4 is called advanced. The numbers only apply when the cancer is staged before initiation of therapy.

Staging the cancer helps physicians determine the best possible treatment plan for you. In general, the less advanced the cancer, the better the prognosis.