Tumor
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Neoplastic tumor of the cheek skin, here a benign neoplasm of the sweat glands called Hidradenoma.

Look up tumor in Wiktionary, the free dictionary.

A tumor or tumour is the name for a swelling or lesion formed by an abnormal growth of cells (termed neoplastic) which may be benign or malignant.

Etymology

The term tumor is derived, via the Old French tumour, from the Latin tumor "swelling".^[1] It originally meant an abnormal swelling of the flesh. In contemporary English, tumor is synonymous with solid neoplasm^[2], all other forms of swelling being called swelling.^[3] This usage is common also in medical literature. Tumor is not precisely synonymous with cancer. A tumor can be benign (pre-malignant) or malignant, whereas cancer is by definition malignant.

The related noun tumefaction, derived from the adjective tumefied, is the current medical term for non-neoplastic tumor.^[4] See also tumescence.

Cause

A neoplasm is an abnormal proliferation of tissues. Where the cause is known, more often than not, a somatic mutation is involved.

Most but not all neoplasms cause a tumor; those that do not cause tumors cause leukemias. Solid neoplasms (or tumors) may be benign or malignant (cancer). For some tumors, such as teratomas, the cancer status is ambiguous; benign or malignant is properly determined retrospectively, after some years of surveillance.

Differential diagnoses of swellings

Swellings may have many causes other than what we now call tumors such as:

• Inflammation, by far the most common cause; tumor is one of the classic signs of inflammation.^[5] The lump following a blow on the head is a typical example. Infection is another common cause of inflammation.
• Edema, the accumulation of an excessive amount of fluid in the tissues, either with or without 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.

References