A Tumor or tumour (via Old French tumour from Latin tumor "swelling") originally meant an abnormal swelling of the flesh. In contemporary English, tumor has evolved to become synonymous with neoplasia, all other forms being called swelling. This tendency is now common in medical literature. The noun tumefaction, derived from the adjective tumefied, is now the favored medical term to designate non-neoplastic tumors.

Tumors and/or swellings can be caused by:

• Neoplasia, a abnormal proliferation of tissues. Most (not all) neoplasms cause a tumor. Neoplasms (or tumors) may be benign or malignant.
• Inflammation, by far the most common cause; tumor is one of the five classic signs of inflammation. The lump following a blow on the head is a typical example. Infection is another common cause of inflammation.
• Malformation, a congenital anomaly in the architecture of a tissue. A typical example is an epidermal nevus.
• Cyst, the accumulation of fluid in a closed structure. Breast cysts are a typical example.
• Hemorrhage in a closed structure.

Other forms of swelling are part of the normal functions of the body and may or may not be included as causes of tumor. Examples include enlargement of the uterus in pregnancy and erection of the penis.

This article is intentionally kept short. For a detailed discussion, see Cancer.

Cancer