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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.
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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, where the nouns tumefaction and tumescence, derived from the adjective tumefied, are the current medical terms for non-neoplastic swelling.[4]
Diagnosis
The nature of the tumor is determined by a pathologist after examination of the tumor tissues from a biopsy or a surgical excision specimen. Tumors may be benign, pre-malignant or malignant (cancer).
Cause
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.
Recent evidence has shown that a tumor cell may be transmissible from one organism to another, where the tumor is caused by the malignant tumor cell itself. This transmission has been observed in dogs with canine transmissible venereal tumor (CTVT), also known as Sticker’s sarcoma. Additionally, this type of transmission has been observed in Tasmanian devils afflicted with Devil facial tumor disease (DFTD). There is no evidence that direct person-to-person transmission of tumor cells occurs during normal social contact. However, transplacental transmission and organ transplantation are known routes of tumor cell transmission.
A group of researchers (Murgia et al.) studying canine transmissible venereal tumor (CTVT), a tumor of dogs, have provided conclusive evidence that a malignant tumor cell has evolved into a transmissible parasite. The tumor cells in dogs from five continents were compared, and all cells were nearly genetically identical. Additionally, the tumor cells are very different from the dogs’ normal cells. This demonstrates that the tumors do not occur from cancerous transformation in individual animals. Rather, the malignant tumor cells from one dog are transferred to another dog via coitus, licking, biting, and sniffing tumor-affected areas. [5]
There is no conclusive evidence that direct person-to-person transmission of tumor cells occurs during common social interactions. However, tumour cells may be passed from mother to her fetus during pregnancy. In the United States every year, approximately 3,500 pregnant women have a malignancy, and transplacental transmission of acute leukaemia, lymphoma, melanoma and carcinoma from mother to fetus has been observed. [6]
Organ transplantation is a possible route of tumor cell transmission, but the development of donor-derived tumors is exceedingly rare. The main cause of organ transplant associated tumors seems to be malignant melanoma, that was undetected at the time of organ harvest. [7]
See also
References
- ^ t_22/12830354 at Dorland's Medical Dictionary
- ^ Tumor in MedlinePlus Medical Encyclopedia
- ^ swelling, in MedlinePlus Medical Encyclopedia
- ^ t_22/12830299 at Dorland's Medical Dictionary
- ^ Murgia C, Pritchard JK, Kim SY, Fassati A, Weiss RA. Clonal origin and evolution of a transmissible cancer. Cell. 2006 Aug 11;126(3):477-87.
- ^ Tolar J & Neglia JP. J. Pediatr. Hematol. Oncol. 25, 430-434 (2003).
- ^ Dingli D, Nowak MA. Cancer biology: infectious tumour cells. Nature. 2006 Sep 7;443(7107):35-6. B).
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- This page was last modified on 30 August 2008, at 17:49.
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