[too-mer, tyoo-]
tumor: see neoplasm.

A tumor or tumour is the name for a swelling or lesion formed by an abnormal growth of cells (termed neoplastic). Tumor is not synonymous with cancer. A tumor can be benign, pre-malignant or malignant, whereas cancer is by definition malignant.


The term tumor is derived, via the Old French tumour, from the Latin tumor "swelling". It originally meant an abnormal swelling of the flesh. In contemporary English, tumor is synonymous with solid neoplasm , all other forms of swelling being called swelling. This usage is common also in medical literature, where the nouns tumefaction and tumescence, derived from the adjective tumefied, are the current medical terms for non-neoplastic swelling.


A neoplasm is an abnormal proliferation of tissues, usually caused by genetic mutations. Most neoplasms cause a tumor, with a few exceptions like leukemia or carcinoma in situ.

Tumors may be benign, pre-malignant or malignant (cancer). The nature of the tumor is determined by a pathologist after examination of the tumor tissues from a biopsy or a surgical excision specimen.

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