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Laboratory animals, particularly mice, are commonly used as human surrogates in cancer research. There are many important reasons for their use. First and foremost is ethics; there are many situations where it is simply unethical to do direct human studies on cancer. Mice are small with a rapid life cycle, which allows for rapid, economical results. Mice are often modified genetically so that they will have greater susceptiblity to certain cancers. These resultant strains of mice, known as models, facilitate the study of specific cancers. Some have questioned whether mice need to be used at all in medical research. Initial cancer studies can take place in vitro, or outside the body, with laboratory apparatus. However, follow-up studies with a species that is physiologically similar to humans are essential in order to study metabolic changes and tumor progression. This article discusses similarities and differences between mice and humans as it relates to cancer, and the application of techniques such as genetic engineering that improve the relevance of mouse models in cancer research. 3)
1. Size and age - Humans are much larger than mice and live much longer. However, at the end of their respective life cycles they have a similar 30% incidence of cancer. 6) The increased age-associated susceptibility of mice may be due to their higher basal metabolic rate. This results in increased generation of oxidants and other mutagens as a result of normal metabolic processes. Additionally, many carcinogens are activated or neutralized quite differently in mouse and human liver. 2. Common types of cancers - Mice tend to develop cancers in cells of mesenchymal tissues (connective and lymphatic tissues and blood vessels), resulting in lymphomas and sarcomas. In contrast, most cancers in humans tend to arise epithelial-cell tissue and lead to carcinomas. 6Rats also develop epithelial tumors more frequently than mesenchymal tumors, (1) but the spectrum of common cancers differs from that of humans. 3. Telomeres and telomerase - Telomeres are short caps of DNA at the ends of chromosomes that are essential in maintaining the stability of the DNA structure. my telomere article Telomeres decrease in size with age until the point where they can no longer perform their function. At this stage, the cell either undergoes senescence (stops dividing), or dies. The enzyme telomerase maintains and extends the telomeres. Telomerase remains active in most mouse cells, but is largely inactive in adult humans. Telomerase thereby helps cells achieve immortality, which is also a hallmark of cancer cells. However, studies have shown that increased telomerase activity does not necessarily promote carcinogenesis.
The copyright of the article Mouse Models in Cancer Research in Cancer Treatment is owned by David Olle. Permission to republish Mouse Models in Cancer Research in print or online must be granted by the author in writing.
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