Skip to main content
Biology LibreTexts

Unit 12: Cancer

  • Page ID
    3771
  • A cancer is an uncontrolled proliferation of cells. In some the rate is fast; in others, slow; but in all cancers the cells never stop dividing. This distinguishes cancers — malignant tumors — from benign growths like moles where their cells eventually stop dividing (usually). Even more important, benign growths differ from malignant ones in not producing metastases; that is, they do not seed new growths elsewhere in the body.

    • 12.1: Cancer in General
      A cancer is an uncontrolled proliferation of cells. In some the rate is fast; in others, slow; but in all cancers the cells never stop dividing. This distinguishes cancers — malignant tumors — from benign growths like moles where their cells eventually stop dividing (usually). Even more important, benign growths differ from malignant ones in not producing metastases; that is, they do not seed new growths elsewhere in the body.
    • 12.2: Cancer Cells in Culture
      Both normal cells and cancer cells can be cultured in vitro in the laboratory. However, they behave quite differently. Normal cells pass through a limited number of cell divisions (70 is about the limit for cells harvested from young animals) before they decline in vigor and die. This is called replicative senescence. It may be caused by their inability to synthesize telomerase.  Cancer cells may be immortal; that is, proliferate indefinitely in culture.
    • 12.3: Oncogenes
      An oncogene is a gene that when mutated or expressed at abnormally-high levels contributes to converting a normal cell into a cancer cell. Cancer cells are cells that are engaged in uncontrolled mitosis. Normal cells growing in culture will not divide unless they are stimulated by one or more growth factors present in the culture medium (e.g, Epidermal Growth Factor (EGF)).
    • 12.4: Tumor Suppressor Genes
      Some genes suppress tumor formation. Their protein product inhibits mitosis. When mutated, the mutant allele behaves as a recessive; that is, as long as the cell contains one normal allele, tumor suppression continues. (Oncogenes, by contrast, behave as dominants; one mutant, or overly-active, allele can predispose the cell to tumor formation).
    • 12.5: BCL-2
      BCL-2 is a human proto-oncogene located on chromosome 18. Its product is an integral membrane protein (called Bcl-2) located in the membranes of the endoplasmic reticulum (ER), nuclear envelope, and in the outer membranes of mitochondria. The gene was discovered as the translocated locus in a B-cell leukemia. This translocation is also found in some B-cell lymphomas.
    • 12.6: Burkitt's Lymphoma
      Burkitt's lymphoma is a solid tumor of B lymphocytes, the lymphocytes that the immune system uses to make antibodies. The genes for making antibodies are located on chromosomes 14 (the heavy [H] chains), 2 (kappa light chains), and 22 (lambda light chains). These genes are expressed only in B lymphocytes because only B cells have the necessary transcription factors for the promoters and enhancers needed to turn these antibody genes "on".
    • 12.7: Chronic Myelogenous Leukemia (CML)
      Leukemia is an uncontrolled proliferation of one kind of white blood cell (or leukocyte). Like all cancers (probably), all the leukemic cells are descended from a single cell that lost the ability to maintain normal control over the cell cycle. There are a number of types of leukemia, as you would expect from the number of types of white blood cells (5) and the number of stages they pass through as they mature. One of the most common is chronic myelogenous leukemia or CML.
    • 12.8: Fighting Cancer with Inhibitors of Angiogenesis
      Once a nest of cancer cells reaches a certain size (1–2 mm in diameter), it must develop a blood supply in order to grow larger. Diffusion is no longer adequate to supply the cells with oxygen and nutrients and to take away wastes. Cancer cells (probably like all tissues) secrete substances that promote the formation of new blood vessels — a process called angiogenesis. Over a dozen substances have been identified that promote angiogenesis.
    • 12.9: Immunotherapy of cancer
      Most cancer patients are treated with some combination of surgery, radiation, and chemotherapy. Radiation and chemotherapy have the disadvantage of destroying healthy as well as malignant cells and thus can cause severe side-effects. One long-held dream is that the specificity of immune mechanisms could be harnessed against tumor cells. This might use the patient's own immune system or the transfer of antibodies or T cells from an outside source.
    • 12.10: Cancer- The Causes and Prevention of Cancer
      The effort to eliminate synthetic pesticides because of unsubstantiated fears about residues in food will make fruits and vegetables more expensive, decrease consumption, and thus increase cancer rates. The levels of synthetic pesticide residues are trivial in comparison to natural chemicals, and thus their potential for cancer causation is extremely low.
    • 12.11: Estimating Cancer Risks
      We live surrounded by radiation and by chemicals that cause mutations in test organisms (like bacteria, yeast, and mice) and cause an increase in the rate of cancers in experimental animals (rats and mice). Is there any safe dose for humans of these agents (which include oxygen!) The question is exceedingly difficult to answer and, I believe, at low doses, unanswerable.
    • 12.12: The LD50 test
      The LD50 is a standardized measure for expressing and comparing the toxicity of chemicals. The LD50 is the dose that kills half (50%) of the animals tested (LD = "lethal dose"). The animals are usually rats or mice, although rabbits, guinea pigs, hamsters, and so on are sometimes used.
    • 12.13: Dioxin
      Name given members of a family of closely-related chemicals. The term dioxin is often used for one of these: 2,3,7,8-tetrachlorodibenzo-p-dioxin or TCDD. This substance was present as a contaminant in the herbicide agent orange, which was so widely used during the Vietnam war. When ingested or injected, TCDD is extremely poisonous to laboratory animals. At sub-lethal concentrations, it causes cancer and birth defects in them.
    • 12.14: Magnetic fields
      "There is no convincing evidence that high-voltage power lines are a health hazard or a cause of cancer...18 years of research have produced considerable paranoia, but little insight and no prevention. It is time to stop wasting our research resources. We should redirect them to research that will be able to discover the true biologic causes of the leukemic clones that threaten the lives of children."

    Thumbnail: This is a photograph of a basal cell carcinoma on the back taken by me. Basal cell carcinoma is the most common skin cancer. (Public Domain; John Hendrix).

    Contributors and Attributions