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Page 17
| Other common forms of cancer include: |
| Melanoma, a cancer of the cells that produce skin pigment. Melanoma is usually found on the skin, frequently in the form of a black mole, especially on the lower limbs, neck, or head. It is one of the most virulent forms of cancer for it can often spread rapidly through the bloodstream and lymphatic vessels to form metastases in many parts of the body. |
| Multiple myeloma, brain, and nerve tissue cancers. These cancers affect either the spinal cord or the brain. Some common forms of these cancers include astrocytoma, medullablastoma, and glioblastoma. |
| Germ cell tumors are cancers that affect those particular cells capable of developing into new cells of the same species, for example, ovum or spermatazoan cells. Examples of these cancers are seminoma, embryonal carcinoma, testicular carcinoma, and yolk sac tumors. |
| Childhood cancers, such as leukemia, neuroblastoma, Wilms' tumor, some brain cancers, and retinoblastoma, are more frequently the result of genetic defects than are other cancers. |
| What Causes Cancer? |
| The cell cycle is regulated by a series of signaling events that consist of positive and negative regulators. Their job is to control the process of cell reproduction, maintaining a balance between positive and negative regulators. |
| Two families of genes that play a role in the cell's signaling processes are oncogenes and tumor-suppressor genes. These genes are usually involved in the initiation of cancer. Damaged or misplaced genes, called proto-oncogenes, are simply genes with oncogenic potential. |
| Normal genes can be altered in a variety of ways, causing them to turn into oncogenes. To date, approximately seventy genes have been shown to be involved in carcinogenesis, some naturally occurring and others induced by a variety of endogenous causes. 4 All cancers are genetically determined to a certain extent, but it is the proto-oncogenes that are targets of a wide range of environmental assaults caused by such factors as chemicals and radiation. It usually takes more than genetic alterations to trigger a cell into cancer growth. |
| Normal cells become cancer cells by an alteration or mutation within the genetic material (DNA) of the cell. Genetic errors brought about by damage |
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