What Is Cancer?

A) The Definition of Cancer

Cancer is a group of diseases characterized by the uncontrolled growth and spread of abnormal cells. If the spread is not controlled, it can result in death. Cancer can start almost anywhere in the human body, which is made up of trillions of cells.

B) Differences between Cancer Cells and Normal Cells

• Growth: Normal cells grow, divide, and die in an orderly manner. Cancer cells continue to grow and divide uncontrollably and do not die when they should.
• Function: Normal cells perform specific functions that benefit the organism. Cancer cells may not perform these functions or may perform them inappropriately.
• Structure: Cancer cells often have an abnormal shape and size compared to normal cells.
• Communication: Normal cells respond to signals that regulate growth and division. Cancer cells ignore these signals.
• Repair: Normal cells can repair DNA damage or die if the damage is too severe. Cancer cells may have defective repair mechanisms, allowing mutations to accumulate.

C) How Does Cancer Develop?

Cancer develops through a multistep process that involves:

1. Initiation: Genetic mutations occur in the DNA of a cell.
2. Promotion: Mutated cells are stimulated to grow and divide.
3. Progression: Cancer cells acquire additional mutations and become more aggressive and invasive.

D) Types of Genes that Cause Cancer

• Oncogenes: Mutated forms of genes that normally help cells grow. When these genes are altered, they can become permanently activated and drive the uncontrolled growth of cancer cells.
• Tumor Suppressor Genes: Genes that normally prevent cell division or cause cell death. When these genes are inactivated, cells can grow uncontrollably.
• DNA Repair Genes: Genes involved in fixing damaged DNA. When these genes are mutated, the cell's ability to repair DNA is impaired, leading to more mutations.

E) When Cancer Spreads

Metastasis is the process by which cancer cells spread from the place where they first formed to other parts of the body. Cancer cells break away from the original tumor, travel through the blood or lymphatic system, and form new tumors in other organs or tissues.

F) Tissue Changes that Are Not Cancer

• Hyperplasia: An increase in the number of cells in an organ or tissue. These cells look normal under a microscope and are not cancerous, but they can become cancerous over time.
• Dysplasia: Cells that look abnormal under a microscope but are not cancer. These cells are more likely than hyperplasia to become cancerous.
• Benign Tumors: Non-cancerous growths that do not spread to other parts of the body and usually do not pose a serious health threat.

G) Types of Cancer

• Carcinomas: Cancers that begin in the skin or tissues that line or cover internal organs. Examples include breast cancer, lung cancer, and colorectal cancer.
• Sarcomas: Cancers that begin in the bones, cartilage, fat, muscle, blood vessels, or other connective or supportive tissue.
• Leukemias: Cancers that begin in the blood-forming tissue of the bone marrow and cause large numbers of abnormal blood cells to be produced and enter the bloodstream.
• Lymphomas: Cancers that begin in the cells of the immune system.
• Central Nervous System Cancers: Cancers that begin in the tissues of the brain and spinal cord.