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A premalignant or precancerous tumor is one that is not yet malignant, but is about to become so.
Examples of premalignant growths include:
Actinic keratosis - also known as senile keratosis or solar keratosis is a premalignant growth consisting of crusty, scaly and thick patches of skin. Fair-skinned people are more susceptible to these types of growths, especially those who are exposed to sunlight (it is linked to solar damage).
Actinic keratoses are seen as potentially premalignant because a number of them progress to squamous cell carcinoma. Doctors usually recommend treating them because of this. There is a 20% risk that untreated lesions eventually become cancerous. Continuous sun exposure increases the risk of malignancy.
Dysplasia of the cervix - the normal cells lining the cervix of the uterus change. The growth can be premalignant, a prelude to cervical cancer. Cervical dysplasia is diagnosed with a PAP smear. According to the National Institutes of Health, USA, about 5% of PAP smears detect the presence of cervical dysplasia. They are more common in women aged 25 to 35. They may be removed with Cryotherapy (freezing), or conization (the cone of tissue from the cervix is removed).
Metaplasia of the lung - the growths occur in the bronchi, tubes that carry air from the windpipe into the lung. The bronchi are lined with glandular cells, which can change and become squamous cells. Metaplasia of the lung is most commonly caused by smoking.
Leukoplakia - thick, white patches form on the gums, bottom of the mouth, insides of the cheeks, and less commonly on the tongue. They cannot be scraped off easily. Experts believe tobacco smoking and/or chewing is the main cause. Although Leukoplakia is rarely dangerous, a small percentage are premalignant and can eventually become cancerous. Many mouth cancers occur next to areas of leukoplakia.
If smokers quit, the condition usually clears up. Quitting both alcohol and tobacco together has better results. The patches can be removed using laser, a scalpel or a cold probe that freezes the cancer cells (cryoprobe).
Malignant tumors divide and spread rapidly, colonizing new areas.
Malignant tumors are cancerous tumors, they tend to become progressively worse, and can potentially result in death. Unlike benign tumors, malignant ones grow fast, they are ambitious, they seek out new territory, and they spread (metastasize).
The abnormal cells that form a malignant tumor multiply at a faster rate. Experts say that there is no clear dividing line between cancerous, precancerous and non-cancerous tumors - sometimes determining which is which may be arbitrary, especially if the tumor is in the middle of the spectrum. Some benign tumors eventually become premalignant, and then malignant.
Metastasis - malignant tumors invade nearby cells, and then the cells near those, and spread. Some cells can break off from the tumor and spread to various parts of the body through the bloodstream or the lymphatic system, and establish themselves anywhere in the body, and form new malignant tumors. Metastasis is the process by which cancer cells spread from their primary site to distant locations in the human body. For example, a patient may have started off with melanoma (skin cancer) which metastasized in their brain.
The cancer cells that metastasize are the same as the original ones. If a lung cancer spreads to the liver, those cancer cells that grow in the liver are lung cancer cells which have acquired the ability to invade other organs.
There are different types of tumors, which are made up of specific types of cancer cells:
Carcinoma - these tumors are derived from the skin or tissues that line body organs (epithelial cells). Carcinomas can be, for example, of the stomach, prostate, pancreas, lung, liver, colon or breast. Many of the most common tumors are of this type, especially among older patients.
Sarcoma - these are tumors that start off in connective tissue, such as cartilage, bones, fat and nerves. They originate in the mesenchymal cells outside the bone marrow. The majority of sarcoma tumors are malignant. They are called after the cell, tissue or structure they arise from, for example fibrosarcoma, liposarcoma, angiosarcoma, chondrosarcoma, and osteosarcoma.
Lymphoma/Leukemia - cancer arises from the blood forming (hematopoietic) cells that originate in the marrow and generally mature in the blood or lymph nodes. Leukemia accounts for 30% of childhood cancers. Leukemia is thought to be the only cancer where tumors are not formed.
Germ cell tumor - these are tumors that arise from a germ cell, pluripotent cells (cells than can turn into any kind of cell). Germ cell tumors most commonly present in the ovary (dysgerminoma) or testicle (seminoma). The majority of testicular tumors are germ cell ones. Less commonly, germ cell tumors may also appear in the brain, abdomen or chest.
Blastoma - tumors derived from embryonic tissue or immature "precursor" cells. These types of tumors are more common in children than adults. Blastoma is often the root word used in longer ones that describe tumors, for example, medulloblastoma and glioblastoma are kinds of brain tumors, retinoblastoma is a tumor in the retina of the eye, osteoblastoma is a type of bone tumor, while a neuroblastoma is a tumor found in children of neural origin.
On the final page, we look at tumor biopsy procedures and the common prefixes used in naming tumors and cancers.