Cancer can begin almost anywhere in the body. Human cells normally grow and multiply to form new cells as the body requires them. Cells die when they become old or damaged, and new cells replace them. When this orderly process fails, abnormal or damaged cells grow and multiply when they should not. These cells have the potential to form tumors. Tumors may or may not be cancerous. Each person's cancer has a unique combination of genetic changes, and as the cancer grows, more changes occur. Even within the same tumor, different cells may have different genetic changes. Cancerous tumors invade nearby tissues and can spread to distant locations in the body to form new tumors. Cancerous tumors are also known as malignant tumors. Many cancers form solid tumors, but cancers of the blood generally do not.

Cancer is a genetic disease—it is caused by changes in genes that control how our cells function, particularly how they grow and divide. Aside from genetics there are certain avoidable/ controllable risk factors, such as smoking, certain lifestyles /sedentary lifestyle/ and radiation exposures, that lead to cancer.