What Is Cancer? A Simple Explanation

Cancer is a disease where some cells in the body grow and divide in an uncontrolled way. These abnormal cells can form a tumour, invade nearby tissues and sometimes spread to other parts of the body.

This article is for general information only. If you have symptoms, a diagnosis or questions about cancer treatment, speak with a doctor or qualified healthcare professional.

How Does Cancer Start?

The body is made of cells. Normally, cells grow, divide and die in a controlled way. Cancer can start when changes in genes affect how cells grow and divide. NCI explains that cancer is caused when cells divide uncontrollably and spread into surrounding tissues, and that it is caused by changes to genes that control cell growth and division. :contentReference[oaicite:4]{index=4}

Benign and Malignant Tumours

Not every lump or growth is cancer. Benign tumours are not cancer and usually do not spread to other parts of the body. Malignant tumours are cancerous and may invade nearby tissue or spread.

Even benign tumours can sometimes cause problems depending on where they grow, so any concerning lump or symptom should be checked by a healthcare professional.

How Cancer Can Spread

Cancer cells can sometimes break away from the original tumour and travel through blood or lymph vessels to other parts of the body. This is called metastasis or cancer spread.

When cancer spreads, it is still usually named after where it started. For example, bowel cancer that spreads to the liver is still bowel cancer, not liver cancer.

What Is Bowel Cancer?

Bowel cancer is cancer that starts in the large bowel, usually in the colon or rectum. It is also called colorectal cancer. Some bowel cancers may develop from polyps over time.

For more detail, read our What Is Bowel Cancer? and Staging Bowel Cancer articles.

How Cancer Is Diagnosed

Cancer may be diagnosed using medical history, physical examination, blood tests, imaging scans, endoscopy, biopsy and laboratory testing. The exact tests depend on the suspected cancer type and symptoms.

For bowel cancer diagnosis, visit our Bowel Cancer Diagnosis guide.

How Cancer Is Treated

Cancer treatment depends on the type of cancer, stage, location, test results and overall health. Treatment may include surgery, chemotherapy, radiation therapy, targeted therapy, immunotherapy, clinical trials or supportive care.

For bowel cancer treatment decisions, read our Making Treatment Decisions for Bowel Cancer article.

Final Thoughts

Cancer is a broad term for diseases involving uncontrolled cell growth. Each cancer is different, so diagnosis, staging and treatment should always be explained by a healthcare professional who knows the person’s medical situation.