Cell Biology and Cancer
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Introduction

"Tumors destroy man in a unique and appalling way, as flesh of his own flesh which has somehow been rendered proliferative, rampant, predatory, and ungovernable . . . Yet, despite more than 70 years of experimental study, they remain the least understood . . . What can be the why for these happenings?" —Peyton Rous, in his acceptance lecture for the Nobel Prize in Physiology or Medicine (1966)

Late in 1910, a young scientist at Rockefeller University was preparing to conduct a most improbable experiment. He wanted to know if one chicken could "catch" cancer from another. At that time, the concept that every cell in the body is derived from another cell was new, and the idea that cancer might involve a disruption of normal cell growth was just taking hold. Thirty years had passed since Louis Pasteur's influential paper on germ theory dislodged the humoral theory of disease that had prevailed for more than 2,000 years, and the prevailing scientific view of cancer emphasized the role of chemical and physical agents, not infectious ones, as potential causes.

Nevertheless, the 30-year-old Peyton Rous was able to show that cell-free extracts from one chicken were able to cause the formation of the same type of tumor when injected into a second chicken. Rous' tumor extracts had been passed through a filter with pores so small that even bacteria were excluded. This result strongly implicated the newly discovered "filterable agents" known as viruses. Rous was later able to demonstrate that other types of chicken tumors could also be spread by their own, unique "filterable agents," and that each would faithfully produce its original type of tumor (bone, cartilage, blood vessel) when injected into healthy animals.

Unfortunately, the full significance of these data was not to be realized for many decades. One reason was the difficulty of reproducing these results in mammals. But another reason was that scientists could not place Rous' discovery in a proper context. So many different things seemed to be associated with cancer that no one was able to make sense of it all. For example,

At the time Peyton Rous accepted his Nobel Prize, it was not clear how these and many other observations would ever be reconciled. By the early 1970s, however, scientists armed with the new tools of molecular biology were about to revolutionize our understanding of cancer. In fact, just over three decades later, Rous would be astounded to learn of the progress made answering his question of "why?"

x-ray view of the human body
Figure 1 - For people touched by cancer, modern science offers better treatment and brighter prospects than ever before.

Cell Biology and Cancer has two objectives. The first objective is to introduce students to major concepts related to the development and impact of cancer. Today we have a picture of cancer that, while still incomplete, is remarkably coherent and precise. Cancer develops when mutations occur in genes that normally operate to control cell division. These mutations prompt the cell to divide inappropriately. Cancer-causing mutations can be induced by a wide variety of environmental agents and even several known viruses. Such mutations also can be inherited—thus, the observation that some families have a higher risk for developing cancer than others. We still have much to learn about cancer, to be sure, but the clarity and detail of our understanding today speak powerfully of the enormous gains scientists have made in just the last 30 years. One objective of this module is to help students catch a bit of the excitement of these gains.

A second objective is to convey to students the relationship between basic biomedical research and the improvement of personal and public health. Cancer-related research has yielded many benefits for humankind. Most directly, it has guided the development of public health policies and medical interventions that today are helping us prevent, treat, and often even cure cancer. A dramatic illustration of the success that scientists and health care specialists are having in the war against cancer came in the 1998 announcement by the National Cancer Institute, the American Cancer Society, and the Centers for Disease Control and Prevention that cancer incidence and death rates for all cancers combined and for most of the top 10 sites declined between 1990 and 1995, reversing an almost 20-year trend of increasing cancer cases and death rates in the United States.

Research is also pointing the way to new therapies, therapies that scientists hope will combat the disease without as many of the devastating side effects of current treatments. For example, the development of drugs that target the genes, proteins, and pathways unique to cancer cells represents a radical leap forward in cancer treatment. Although most of these drugs are only beginning to be tested, preliminary results offer reason for enthusiasm about the prospects of controlling cancer at its molecular level.

And cancer research has yielded other benefits as well. In particular, it has vastly improved our understanding of many of the body's most critical cellular and molecular processes. The need to understand cancer has spurred research into the normal cell cycle, mutation, DNA repair, growth factors, cell signaling, and cell aging and death. Research also has led to an improved understanding of cell adhesion and anchorage, the "address" system that keeps normal cells from establishing themselves in inappropriate parts of the body, angiogenesis (the formation of blood vessels), and the role of the immune system in protecting the body from harm from within as well as without.

This module addresses our progress in understanding the cellular and molecular basis of cancer and considers the impact of what we have learned for individuals and society. There are many concepts we could have addressed, but we have chosen, with the help of a wide variety of experts in this field, a relatively small number for exploration by your students. Those concepts follow.

We hope that the five activities provided in this module (Figure 2) will be effective vehicles to carry these concepts to your students. Although the activities contain much interesting information about various types of cancer, we suggest that you focus your students' attention on the major concepts the module was designed to convey. The concluding steps in each activity are intended to remind students of those concepts as the activity draws to a close.

Figure 2 - This diagram identifies the module's major sections and describes their contents.
Student Activity 1
The Faces of Cancer
Student Activity 2
Cancer and the Cell Cycle
Student Activity 3
Cancer as a Multistep Process
Student Activity 4
Evaluating Claims About Cancer
Student Activity 5
Acting on Information About Cancer
Students participate in a role play about people who develop cancer, assemble data about the people’s experiences with cancer, then discuss the generalizations that can be drawn from these data. Students use five Web-based animations to help them construct an explanation for how cancer develops, then use their new understanding to explain several historical observations about agents that cause cancer. Students use random number tables and a Web-based simulation to test several hypotheses about the development of cancer. Students identify claims about UV exposure presented in a selection of media items, then design, execute, and report the results of an experiment designed to test one such claim. Students assume the roles of federal legislators and explore several Web-based resources to identify reasons to support or oppose a proposed statute that would require individuals under the age of 18 to wear protective clothing when outdoors.
 

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