Neoplasms: Excerpt 8

Neoplasms: principles of development and diversity was published October 1, 2008. In the next few blogs, I will provide some short excerpts from the book.

Excerpt from the Introduction to Chapter 5, "What Can We Learn About Human Neoplasms by Studying Animals, Plants, Fish, and Insects?"

Bacteria, protoctists, fungi, plants, and animals all share constitutive molecules and pathways, and they all derive from the same primordial organism.

Unicellular organisms, bacteria and protoctists, do not develop cancer. There are bacterial mutants that grow more rapidly than their wild-type counterparts, but there are no instances of cancerous bacteria that dominate the bacterial world, replacing all bacterial flora in a biological system (such as the gut) with an unregulated mutant clone. Presumably this is because unregulated growth is not a particularly useful feature for a single-cell organism. Organisms need to know when to become quiescent. Unregulated growth, occurring when food supply is limited or when growth conditions are suboptimal, does not provide a survival advantage.

The kingdoms of plants (Plantae) and animals (Animalia) share a susceptibility to cancer. In both of these kingdoms, organisms consist of growing amalgams of different kinds of cells. The cells in plants and animals become specialized, with particular cells differentiating along particular developmental lineages due to epigenomic programming. It seems that these features (growth, multicellularity, and differentiated cell types) provide the necessary setting for the occurrence of neoplasms.

The question posed in the chapter title,"What can we learn about human neoplasms by studying animals, plants, fish, and insects?" is often misconstrued to mean, "What are the animal models for human cancer?" Sadly, much of the history of cancer research has involved the search for cancers in rodents and other animals that closely mimic some human cancer. Traditionally, if an animal tumor has a similar morphology and biological behavior to a human cancer, it is thought to be suitable for human cancer studies (testing for potential human carcinogens, developing human tumor markers, or developing new therapeutic agents). Although progress has been achieved through the "animal model" approach of comparative pathology, many detractors believe that animal models are wasteful, time consuming, and cruel. A large community of animal activists has become repulsed by large-scale testing studies on rodents and other animals and has called for the cessation of many experiments that subject animals to toxic agents and surgical procedures.

The purpose of chapter 5 is to show that we can learn a great deal about human cancer simply by observing the natural occurrences of neoplasms in plants and animals. A naturalist's approach to comparative pathology will show that we learn more by observing differences between one organism and another than by observing similarities. We see in Chapters 6 and 14 that the methods of animal classification serve as the basis for the classification of human neoplasms.

(to be continued)

The full table of contents is available. In the next few days, I will continue to discuss content from Neoplasms in my blogs.

-Jules Berman

Key words: tumors, tumour, neoplasms, neoplasia, carcinogenesis, tumor development, cancer research, neoplastic development, precancer preneoplasia, preneoplastic