病毒和癌癥

除了化學物質和輻射之外, 病毒（viruses）也是壹種突變的原因。病毒是非常小的“有機體”，能感染其它動物或植物。人類對許多病毒都容易受到感染。病毒與細菌（bacteriaA microscopic organism. Bacteria lack a nucleus. They are found in very large numbers in almost all locations, including the human body. While most bacteria are harmless or necessary, some can cause disease and death.）不屬同壹類，但是它們都會導致人類疾病。治愈細菌性感染的藥物對病毒性疾病是無用的。病毒的例子有：導致流行性感冒的“流感病毒”、導致獲得性免疫缺陷綜合征／艾滋病（AIDS）的人類免疫缺陷病毒／艾滋病病毒（HIV ）。

病毒以下面幾種不同方式幹擾細胞活動：

  • 病毒可以直接損害DNAAbbreviation for deoxyribonucleic acid. Composed of very long strings of nucleotides, which are abbreviated as A, C, G and T. DNA is the storage form of our genetic material. All of the instructions for the production of proteins are encoded in our DNA. （突變）。這是通過將病毒的基因組（genomes） 插進宿主細胞的DNA 。這樣形成的結合體能擾亂重要調節基因的活動。
  • 病毒可以含有它們自己的基因，其能擾亂細胞的調節 。如果這個過程能允許病毒迅速繁殖後代，那麽會對病毒十分有利，但對宿主有很大危害性。
  • 壹些病毒攜帶著從之前的宿主細胞內獲得的變異基因復制本 。這些變異基因不再有正常功能。當它們被插進新的宿主細胞中，則會導致調節紊亂，甚至惡性腫瘤的生長。

通過病毒的突變原（mutagenicCausing alterations to DNA. If the alterations are not repaired exactly, changes in the DNA can lead to altered gene expression or gene products. Many mutagens are also carcinogens, agents that can cause cancer. Since cancer results from mutations in key genes, an agent that can cause changes has the potential to cause the changes that lead to cancer. Ironically, radiation and many of the chemotherapy agents used to treat cancer also have the potential to cause mutations and lead to cancer themselves.）活性或它們對細胞行為方式的影響，病毒在許多不同動物（包括人類）的某些惡性腫瘤的生長上起著十分重要的作用。

病毒壹直是惡性腫瘤科研中的壹個重要課題。壹些初期科研就是用病毒對癌基因（oncogenes）和腫瘤抑制基因（tumor suppressors）進行識別鑒定。1

病毒大致分為兩類：以DNA為遺傳物質的DNA 病毒與以RNAAlso: ribonucleic acid. RNA is a polymer comprised of the nucleotides A, C, G and U. RNA is the working form of our genetic information. RNA is produced via the process of transcription. Some RNA is used to help build ribosomes (rRNA) and some (mRNA) are used to guide the formation of proteins. Other forms of RNA are used to perform specialized functions in the nucleus.為遺傳物質的 RNA 病毒。這兩類病毒都與許多種惡性腫瘤有關。這些與DNA病毒有關的惡性腫瘤有：宮頸癌（乳頭狀瘤病毒）、肝癌（B 型肝炎病毒）、非洲伯基特氏淋巴瘤（lymphomaA cancer arising in the lymphatic system. The white blood cells affected are part of the body's immune system. The lymphatic system is a large network of vessels that carry fluid and cells of the immune system around the body. Lymph nodes are regional collection centers in the lymphatic system. See also, 'lymphatic system'.）（愛- 巴二氏病毒，Epstein-Barr 病毒） 等。與RNA病毒有關的至少有壹種 白血病（leukemiaA cancer affecting the cells that develop into white or red blood cells. Both of these cell types originate from stem cells in bone marrow. Red blood cells function to carry oxygen to our tissues and the white cells (leukocytes) are part of our immune system. The cancerous cells often accumulate in the blood. ）。

  • 1. Cooper G. Oncogenes. Jones and Bartlett Publishers, 1995. 151-152, 175-176.