Overview

The word "cancer" refers to abnormal cells that grow uncontrollably. Cancer is not a single disease. It can involve any type of cell, anywhere in your body. And it starts with a problem in the cell's genes.

Damaged Cells

All cells contain genes that control how they grow, divide and eventually die. But these genetic instructions can become damaged. For example, too much sunlight damages genes in skin cells. Cigarette smoke damages genes in lung cells. In most other cases, the exact cause of the damage is not known.

Uncontrolled Growth

When its genes are damaged, a cell may grow uncontrollably. The abnormal cell may live beyond its normal lifespan, dividing again and again. And the new cells it produces inherit the damaged genes. When these cells grow into a mass without invading healthy tissues, this is called a "benign" growth. Benign cells are not cancer. But when abnormal cells grow uncontrollably and also invade healthy tissues, they are called "malignant," and "cancerous." This is cancer.

How Cancer Spreads

Cancer cells can form lumps of abnormal cells called "tumors." Cancer cells can also spread to other parts of the body, commonly through the bloodstream or the lymphatic system. For example, cancer cells that form in the colon may spread to the liver or the lungs. When cancer cells spread from one part of the body to another, the cancer is said to have "metastasized."

Treatment

Different types of cancer can behave very differently. There isn't just one way to treat cancer. Your doctor can explain the pros and cons of treatment options such as surgery, chemotherapy and radiation therapy. Your healthcare team will work with you to develop a care plan that is right for your needs.