Rectal cancer

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The term cancer is very broad and covers many different illnesses including:

  • Carcinoma (arising from epithelial cells)
  • Bladder carcinoma
  • Breast cancer
  • Cervical cancer
  • Colorectal cancer (includes colon, rectum, anus, and appendix)
  • Esophageal cancer
  • Endometrial cancer (uterus)
  • Hepatocellular carcinoma (liver)
  • Laryngeal cancer
  • Lung cancer
  • Oral cancer
  • Ovarian cancer
  • Pancreatic cancer
  • Prostate cancer
  • Renal cell carcinoma (kidney)
  • Skin cancer
  • Stomach cancer
  • Testicular cancer
  • Thyroid cancer
  • Sarcoma (arising from connective tissue and related)
  • Gastrointestinal stromal cell tumor (GIST)
  • Rhabdomyosarcoma (muscle)
  • Osteosarcoma (bone)
  • Hematological malignancies (blood and bone marrow)
  • Leukemia
  • Lymphomas
  • Hodgkin's disease
  • Non-Hodgkin's lymphoma
  • Multiple myeloma
  • Miscellaneous
  • Brain tumor
  • Melanoma, Moles and dysplastic nevi
  • Teratoma

Cancer is, ultimately, a disease of genes. Typically, a series of several mutations is required before a cell becomes a cancer cell. We distinguish between oncogenes, which promote cancer when "switched on" by a mutation, and tumor suppressor genes, which prevent cancer unless "switched off" by a mutation. These mutations can have various causes: radiation or chemicals called carcinogens; some inherited predisposition is not uncommon; some viruses that can cause cancer have also been described. Usually, they carry in their genome some oncogene or tumor suppressor inactivating gene. In about 15% of all cancers, viruses seem to play a role; Bacteria, like Helicobacter pylori, also induce carcinogenesis by a process of chronic inflammation. Finally, damage by free radicals, which are a natural by-product of oxygen metabolism, can cause mutations in the DNA.

A cell that degenerates into a tumor cell does usually not acquire all these properties at once, but its daughter cells are selected to build them. This process is called cellular evolution. A first step in the development of a tumor cell is usually a small change in the DNA, often a point mutation, which leads, among other things, to a genetic instability of the cell. The instability increases to a point where the cell loses whole chromosomes, or has double ones. Also, the DNA methylation pattern of the cell changes, activating and deactivating genes more or less at random. Cells that divide at a high rate, such as stem cells, show a higher risk of becoming tumor cells than those which divide less or not at all, for example neurons. If the initial tumor cell (or group of tumor cells) is not removed by the immune system, it will develop into cancer.