Overview

Cancer begins when normal cells begin to change and grow uncontrollably, forming a mass called a tumor. A tumor can be benign (noncancerous) or malignant (cancerous, meaning it can spread to other parts of the body).

Mesothelioma is a rare cancer that begins in the lining of the internal organs of the body. Approximately three-fourths of mesotheliomas begin in the lining surrounding the lungs, called pleural mesothelioma. While pleural mesothelioma does begin in the chest cavity, it does not start in the lungs, and it is often incorrectly grouped with lung cancer. Mesothelioma that begins in the tissue surrounding the abdominal area, called peritoneal mesothelioma, accounts for about 10% to 20% of mesotheliomas. The rarest type of mesothelioma begins in the lining around a man’s testicles, called the tunica vaginalis.

There are three main types of mesothelioma:

Epithelioid type. The epithelioid type accounts for about 70% of people diagnosed with mesothelioma. It has the best prognosis (chance of recovery) because it may grow slower and is more likely to respond to treatment.

Sarcomatoid type. The sarcomatoid type accounts for 7% to 20% of people diagnosed with mesothelioma and has a worse prognosis. It generally does not respond well to chemotherapy.

Mixed, or biphasic, type. The mixed type accounts for 10-20% of people diagnosed with mesothelioma and contains both epithelioid and sarcomatoid types. This type of mesothelioma has an intermediate prognosis.

Find out more about basic cancer terms used in this section.