| Carcinogenesis is the creation of a cancer. | | | | body by two mechanisms: local invasion and |
| | | | distant metastasis. Invasion refers to the |
| Cancer is, ultimately, a disease of genes. | | | | direct migration and penetration by cancer |
| Typically, a series of several mutations is | | | | cells into neighboring tissues. Metastasis |
| required before a cell becomes a cancer cell. | | | | refers to the ability of cancer cells to |
| We distinguish between oncogenes, which | | | | penetrate into lymphatic and blood vessels, |
| promote cancer when "switched on" by a | | | | circulate through the bloodstream, and then |
| mutation, and tumor suppressor genes, which | | | | invade normal tissues elsewhere in the body. |
| prevent cancer unless "switched off" by a | | | | Cancer is most deadly when it metastasizes. |
| mutation. These mutations can have various | | | | |
| causes: radiation or chemicals called | | | | Forms of cancer |
| carcinogens; some inherited predisposition is | | | | |
| not uncommon; some viruses that can cause | | | | The term cancer is very broad and covers many |
| cancer have also been described. Usually, | | | | different illnesses including: |
| they carry in their genome some oncogene or | | | | |
| tumor suppressor inactivating gene. In about | | | | Bladder cancer |
| 15% of all cancers, viruses seem to play a | | | | |
| role. Finally, damage by free radicals, which | | | | Bone cancer |
| are a natural by-product of oxygen | | | | |
| metabolism, can cause mutations in the DNA. | | | | Brain tumor |
| | | | |
| For most of the cancers, it cannot be told | | | | Breast cancer |
| which event was the initial cause. However, | | | | |
| with molecular biology, it is possible to | | | | Cervical cancer |
| characterize the mutations within a tumor, | | | | |
| and to a certain extent to predict its | | | | Colorectal cancer (includes colon, rectum, |
| behavior. For example, about half of the | | | | anus, and appendix) |
| tumors are deficient in the tumor suppressor | | | | |
| gene p53, also known as "the guardian of the | | | | Cancer of the esophagus |
| genome". This is associated with poor | | | | |
| prospects for the patient, since those tumor | | | | Hodgkin's disease |
| cells are unlikely to go into apoptosis | | | | |
| (programmed cell death) after they are | | | | Kidney cancer |
| damaged by therapy. There are more mutations | | | | |
| that make a tumor more malignant. Telomerase | | | | Cancer of the larynx |
| mutations enable a tumor cell to divide | | | | |
| indefinitely. Other mutations enable the | | | | Leukemia |
| tumor to grow new blood vessels to feed it, | | | | |
| or to detach from the surrounding tissue, | | | | Liver cancer |
| spreading to other parts of the body. | | | | |
| | | | Lung cancer |
| Malignant tumors such as carcinoma or | | | | |
| sarcoma, lymphoma or leukemia originate from | | | | Lymphoma |
| a cell or a group of cells in a multicellular | | | | |
| organism that have several distinct | | | | Melanoma |
| properties:increased cell division ratenot | | | | |
| controllable by growth factors anymorealtered | | | | Moles and dysplastic nevi |
| differentiation (specialization) abilityno | | | | |
| ability for contact inhibitionability to | | | | Multiple myeloma |
| invade neighbouring tissueability to build | | | | |
| metastasesability to promote blood vessel | | | | Muscular Cancer |
| growth | | | | |
| | | | Non-Hodgkin's lymphoma |
| A cell that degenerates into a tumor cell | | | | |
| does usually not acquire all these properties | | | | Oral cancer |
| at once, but its daughter cells are selected | | | | |
| to build them. This process is called | | | | Ovarian cancer |
| cellular evolution. A first step in the | | | | |
| development of a tumor cell is usually a | | | | Cancer of the pancreas |
| small change in the DNA, often a point | | | | |
| mutation, which leads, among other things, to | | | | Prostate cancer |
| a genetic instability of the cell. The | | | | |
| instability increases to a point where the | | | | Skin cancer |
| cell loses whole chromosomes, or has double | | | | |
| ones. Also, the DNA methylation pattern of | | | | Stomach cancer |
| the cell changes, activating and deactivating | | | | |
| genes more or less at random. Cells that | | | | Testicular cancer |
| divide at a high rate, such as stem cells, | | | | |
| show a higher risk of becoming tumor cells | | | | Teratoma |
| than those which divide less or not at all, | | | | |
| for example, neurons. If the initial tumor | | | | Thyroid cancer |
| cell (or group of tumor cells) is not removed | | | | |
| by the immune system, it will develop into | | | | Cancer of the uterus |
| cancer. | | | | |
| | | | Clinical aspects |
| In cellular model systems, cells are exposed | | | | |
| to carcinogenic influences (chemicals, | | | | The field of medicine concerned with the |
| radiation). In these systems, the first signs | | | | treatment of cancer is oncology. |
| of a cell developing into a tumor cell are : | | | | |
| | | | Cancer has become an important problem with |
| Immortality. The usual number of cell | | | | the rise in life expectancy, as the above |
| divisions for a mammalian cell is 50-60 (cell | | | | mentioned mutations become more likely the |
| senescence), then it ceases to divide. Tumor | | | | longer a person lives. Though great progress |
| cells keep dividing forever. | | | | in treatment has been made, most cancers in |
| | | | advanced stages remain incurable and |
| Altered morphology. | | | | ultimately fatal. |
| | | | |
| Building of cellular clusters (Foci). | | | | Treatment of cancer typically involves |
| | | | surgery to remove tumors and nearby lymph |
| Loss of contact inhibition. | | | | nodes to which the cancer may have spread, |
| | | | combined with radiation therapy and/or |
| Low or no need for growth factors. | | | | chemotherapy. The latter two target cells in |
| | | | the body that are rapidly dividing. This |
| Metastasis | | | | includes the cancer cells but also certain |
| | | | healthy ones, which is the reason for the |
| Cancers are capable of spreading through the | | | | severe side effects of these treatments. |