Tumor cells occupy space that are not prepared for them, injuring the tissues where they stay, replacing or altering their duties.
They stimulate the formation of blood vessels to feed, oxygen and to continue growing.
They obtain the ability to invade, by the blood and lymphatic torrent and to develop in other tissues or organs, which is known as metastasis. When the tumor spreads to another organ, it doesn´t change its name, remains where it had origin.

Cancer develops when abnormal cells grow out of control in a part of the body. Normal body cells grow, divide, and die in an orderly fashion, in most parts of the body they divide only to replace worn-out or dying cells and to repair injuries.
Instead of dying, cancer cells continue to grow and divide, they outlive normal cells and continue to form new abnormal cells.(The process is called apoptosis)
Cancer cells develop because of damage to DNA. This substance is in every cell and directs all activities. Most of the time when DNA becomes damaged the body is able to repair it. In cancer cells, the damaged DNA is not repaired. People can inherit damaged DNA, which accounts for inherited cancers. (familiy predisposition)
More often, though, a person’s DNA becomes damaged by exposure to something in the environment (smoking or chemical agents) or through the years they generate tumor cells.

Cancer usually forms as a tumor, except for the leukemia that involve the blood and blood-forming organs and circulate through other tissues where they grow.
Often, cancer cells travel to other parts of the body where they begin to grow and replace normal tissue. This process is called metastasis.
Regardless of where a cancer may spread, however, it is always named for the place it began. For instance If a lung cancer spreads in bones is not called bone cancer, but lung cancer with bone metastasis)

Not all tumors are cancerous. Benign (noncancerous) tumors do not spread (metastasize) to other parts of the body and, with very rare exceptions, are not life threatening, the y are removed by surgery.
A carcinoma is a cancer which is derived from the lining cells, or epithelium, of an organ.There are 4 major types of epithelium in the body (Glandular, squamous, transitional, and pseudostratified)
Carcinomas can arise from any of these epithelial types.
A sarcoma is a cancer derived from the soft tissues of the body. Soft tissues include the fat, muscle, nerves, and connective tissue support. Although not usually soft, it also includes bone and cartilage.
A lymphoma is a cancer derived from the white blood cells that are present in the lymphoid tissues of the body. These sites most commonly include the lymph nodes and spleen. However, lymhomas may arise from any organ and body site.
A melanoma is a cancer derived from melanocytes. These are the pigment producing cells present in the skin. A mole is a benign growth of melanocytes.
There is a change in the biological behavior, not only among the differents types of tumors, but also in those that have the same origin.

At the time of diagnosis is important to realize the stage of disease since the tumor would have more chances of treatment the smaller size it has.