Cancer is a disease in which the body's cells grow uncontrollably and unconditionally. It may start anywhere in the body. It may begin in a cell/tissue or body part and remain in that specific region or spread to the surroundings or remote parts of the body.

Generally, normal cells die after a certain period or because of any damage to it. This process repeats, and new cells take their places. However, in cancer, cells start to grow uncountable through cell division, and they do not die after a certain period (a natural mechanism of cell growth). 

These uncontrollable grown cells accumulate and form a tissue lump or tumor. Some cancers, like leukemia, multiple myeloma, or lymphoma, are confined to blood. The rest of the cancers are solid tumor-type cancers, like breast, lung, colorectal, or prostate cancers.

All tumors are not cancerous. The cancerous tumors are known as malignant tumors, and they spread to different parts of the body. After removing malignant tumors, sometimes they retain and start to grow again.

Non-cancerous tumors are known as benign tumors, and they do not spread. After they are removed, they do not grow again. These are not cancerous, but sometimes, they may be life-threatening.