Evolution and cancer

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Revision as of 14:58, 9 April 2008

Evolution and Cancer

Lesson Overview Students read a brief passage that introduces the concept that the development of cancer is analogous to evolution. They learn about the characteristics of cancer cells by viewing the “Hallmarks of Cancer” section of the www.insidecancer.org site. For each hallmark of cancer, they write a brief summary statement explaining how that hallmark makes cancer cells more “fit” in the competition with normal cells. Students then do a class simulation that illustrates how multiple mutations lead to the evolution of normal cells into a population of malignant cancer cells.

Goals and Objectives

Students will: 1. explain the hallmarks that distinguish a normal cell from a cancer cell.

2. analyze and interpret the results of a simulation that illustrates the transformation of normal. cells into malignant and drug resistant cancer cells.

3. apply the concept of natural selection to understanding cancer evolution

Assumptions of Prior Knowledge Students should have a basic understanding of:

• evolution and natural selection.

• normal cell structure and function.

• mitosis and genetics (particularly characteristics of DNA and mutations which may occur) would be helpful.

Common Misconceptions

Students do not clearly understand that the progression from normal cells to cancer cells typically involves multiple mutations (“multiple hits”). Students may recognize that cancer involves uncontrolled cell division, but they rarely understand that cancer cells have other characteristics that affect their reproduction and survival. Students may think that in the future scientists will discover a single cause for all types of cancer.

Students may think that evolution only happened in the distant past. They may not realize that evolutionary biology has an impact on their future. Students may think that evolution only results in the production of new species.

The Lesson

For a Word document including this lesson plan, including student handouts, go here: Image:Evolution and Cancer Lesson Plan.doc

Preparation Before class: (materials, handouts etc.)

• Photocopy one Cancer and Evolution student sheet for each student. (See Appendix A)

• Photocopy one Table 1. The Evolution of Cancer for each student (See Appendix B)

• Photocopy (laminate or put in sheet protectors) 15 sets of the Mutation Cards—A-K. Printing the backs of the card is optional. Shuffle the mutation cards. (See Appendix C)

• Photocopy 1 set of student signs (1-10). Laminate or put in sheet protectors. Attach string to the signs so that students can hang them around their necks. (See Appendix D)

During class

• Before starting the lesson, assess students’ prior knowledge by having them to answer the following questions:

o How are normal cells different from cancer cells?

o How are normal cells similar to cancer cells?

• Hand out the Evolution and Cancer student sheets. Read the three introductory paragraphs for Part 1 aloud.

• Ask students to go to http://www.insidecancer.org. Provide students with information about how to find “Hallmarks of Cancer” section of the site and how to navigate within this section.

• Allow at least 30 minutes for students to view the information in the “Hallmarks of Cancer” section. For each hallmark, they should explain how that hallmark makes cancer cells more “fit” for competing, surviving and reproducing in the body’s internal environment.

• Select 10 students to be participants in the simulation. Give each player a sign (1-10) and ask them to wear the signs. Ask these students to move to the front of the room.

• Read the first four paragraphs in Part 2, aloud, to the class.

• Read the instructions for the simulation, aloud, and have student participants follow the instructions. Note, student participants do not record data during the simulation. Participants can use data tables created by other students in the class to answer the questions at the end of the simulation. All students who are not participants should record the “data” as described in the instructions. (Optional: create a single class data table on a transparency).

• Hints for the simulation:

      o	Project a “class data table” and model how to record data for at least the first three generations.
      o	 Consider providing markers so that students can mark the letters that represent the hallmarks of cancer.  
      o	A sample of how to fill in the data table and tally the columns is provided in the teacher answer key.

• At the end of the simulation, ask students to complete the questions in Part 2.

• If time permits, revisit the lists students made describing the ways in which cancer cells are different from and similar to normal cells. They could add to these lists. Consider asking students what questions they have about cancer cells or evolution.

Time required

Part 1—Approximately 40 minutes

Part 2—Approximately 40 minutes

Student Handouts for the Lesson Plan

See Appendix A-E in the attached word file for the student handouts for this lesson.

Alternative Assessments • Explain 5 ways in which cancer cells are different from normal cells.

• The cells that make up a tumor exhibit variation—they contain different combinations of mutations. Explain why this important for the evolution of pre-cancerous cells into a highly malignant cancer cells.

• Describe 5 characteristics of cancer cells that make them “fit” for surviving and reproducing.

• See Appendix E for a sample quiz.

• Make a labeled cartoon or cartoon strip that illustrates the characteristics of the “World’s Most Fit Cancer Cell.” Include all of the hallmarks of cancer.

• Make a CD cover and descriptive play list for a CD that illustrates the hallmarks of cancer.

Suggestions for Extended Learning

• The “Hallmarks of Cancer” section focuses on the functions that enable cancer cells to survive and reproduce. Explore the Diagnosis and Treatment—Pathology section in the Inside Cancer site. How do pathologists tell the difference between normal cells and cancer cells?

• Read the original article that proposed the “Hallmarks of Cancer” by Douglas Hanahan* and Robert A. Weinberg† available at Hallmarks of Cancer . Select one of the Hallmarks of Cancer that you find most interesting. Create 6 new “web cards” that could be added to the related section of the InsideCancer.org web site.

• Do an Internet search to learn more about the cancer research career of Bruce Stillman, Ph.D., Douglas Hanahan, Ph.D, or Robert Weinberg, Ph.D. Write a biography that describes their life, their interests, and their accomplishments in cancer research.

• Read about the work of Carlo C. Maley, Ph.D. at Maley. Explain three examples of ways in which his research could be used to develop ways to prevent or cure cancer.

• Visit Simcancer and read “Development of a powerful new computer simulation of tumor growth sets the stage for customized cancer treatment” to learn how computer scientists and mathematicians are studying cancer using a computer modeling program called SimCancer.

• Visit Cancer Curricula for a variety of cancer education curriculum units developed by Cancer Education Project at the University of Rochester’s Life Sciences Learning Center.

• Consider purchasing the CellServ Normal and Cancer Cells in Vitro kit from http://www.cellserv.org/Kits/Kit1.html. Using this kit, each student will be led through a step by step procedure which involves staining, mounting, and observation of normal and transformed (tumor) cells. Each student will observe the morphological differences, as well as the differing growth patterns of these cell types when grown in culture. The site also provides PowerPoints to accompany the lab kit.

Glossary -

Apoptosis A form of cell death in which a programmed sequence of events leads to the elimination of cells without releasing harmful substances into the surrounding area. When programmed cell death does not work properly, cells that should be eliminated may survive.

Angiogenesis The process of developing new blood vessels. Angiogenesis is important in the normal development of the embryo and fetus. It also appears important to tumor formation.

Metastasis The process by which cancer spreads from the place at which it first arose as a primary tumor to distant locations in the body. Metastasis depends on the cancer cells acquiring two separate abilities -- increased motility and invasiveness.

Telomere The end of a chromosome, a specialized structure involved in the replication and stability of the chromosome. Many normal human cells progressively lose terminal TTAGGG sequences from their chromosomes during the process of cell division, a loss associated with stopping the cell division cycle. Failure of telomeres to shorten may lead to cellular immortality.

National Science Education Standards

Unifying Concepts and Processes

• Living systems also have different levels of organization--for example, cells, tissues, organs, organisms, populations, and communities. Within these systems, interactions between components occur. Further, systems at different levels of organization can manifest different properties and functions.

• Models are tentative schemes or structures that correspond to real objects, events, or classes of events, and that have explanatory power. Models help scientists and engineers understand how things work. Models take many forms, including physical objects, plans, mental constructs, mathematical equations, and computer simulations.

• Evolution is a series of changes, some gradual and some sporadic, that accounts for the present form and function of objects, organisms, and natural and designed systems. The general idea of evolution is that the present arises from materials and forms of the past. Although evolution is most commonly associated with the biological theory explaining the process of descent with modification of organisms from common ancestors, evolution also describes changes in the universe. Life Science

• Cells have particular structures that underlie their functions. Every cell is surrounded by a membrane that separates it from the outside world. Inside the cell is a concentrated mixture of thousands of different molecules which form a variety of specialized structures that carry out such cell functions as energy production, transport of molecules, waste disposal, synthesis of new molecules, and the storage of genetic material.

• Cells store and use information to guide their functions. The genetic information stored in DNA is used to direct the synthesis of the thousands of proteins that each cell requires.

• Cell functions are regulated. Regulation occurs both through changes in the activity of the functions performed by proteins and through the selective expression of individual genes. This regulation allows cells to respond to their environment and to control and coordinate cell growth and division.

• In all organisms, the instructions for specifying the characteristics of the organism are carried in DNA, a large polymer formed from subunits of four kinds (A, G, C, and T). The chemical and structural properties of DNA explain how the genetic information that underlies heredity is both encoded in genes (as a string of molecular "letters") and replicated (by a templating mechanism). Each DNA molecule in a cell forms a single chromosome.

• Changes in DNA (mutations) occur spontaneously at low rates. Some of these changes make no difference to the organism, whereas others can change cells and organisms. Only mutations in germ cells can create the variation that changes an organism's offspring.

• Species evolve over time. Evolution is the consequence of the interactions of (1) the potential for a species to increase its numbers, (2) the genetic variability of offspring due to mutation and recombination of genes, (3) a finite supply of the resources required for life, and (4) the ensuing selection by the environment of those offspring better able to survive and leave offspring. Science in Personal and Social Perspectives

• The severity of disease symptoms is dependent on many factors, such as human resistance and the virulence of the disease-producing organism. Many diseases can be prevented, controlled, or cured. Some diseases, such as cancer, result from specific body dysfunctions and cannot be transmitted.

Teacher Answer Key for Evolution and Cancer

Part 1 Growing uncontrollably

Cancer cells do not respond to signals that usually regulate cell growth and division. They grow in the absence of growth signals. Cancer cells grow in the presence of growth inhibitory signals that normally succeed in stopping the division of normal cells.

Evading death

Cancers cells do not undergo apoptosis (commit suicide) when they are damaged.

Processing Nutrients

Cancer cells carry out angiogenesis to attract blood vessels to grow into the tumor mass to provide oxygen and nutrients.

Becoming immortal

Cancer cells turn on an enzyme called telomerase that ensures the telomeres stay very long. This allows the cell to continue dividing indefinitely.

Invading tissues

Cancer cells invade and metastasize to spread to other sites in the body.

Avoiding detection

Cancer cells must avoid detection by the B cells and T cells of the immune system. These cells destroy emerging pre-cancerous cells are normally eliminated by the immune response.

Promoting Mutation

Cancer cells have mutations, deletion of whole genes, or extra copies of genes that lead to genomic instability.

Part 2

Sample to illustrate how to fill in Table 1. The Evolution of Cancer

1. How many cancer cells were “fit” enough to survive the competition? Answers will vary. You may wish to tell students that the mutation rate for genes is very low, so in their bodies ,the chance of getting a mutation that might lead to cancer is low.

2. In your own words, describe the characteristics of one of the “fit” cancer cells that survived to the 10th generation. Answers will vary but student answers should reflect an understanding that the “fit” cells are the ones typically have multiple characteristics enabling them to survive and reproduce.

3. Explain why older people are more likely than other people to develop cancer. As people age, they are more likely to have accumulated the multiple mutations that are usually needed to turn a normal cell into a cancer cell.

4. Which cancer cell player would be able to survive and reproduce if the chemotherapy treatment had included both drug “Y” and drug “Z.” Answers will vary. It is possible that no surviving player is resistant to both chemotherapy drugs.

5. Explain why doctors often use two different chemotherapy drugs to prevent the evolution of cancer cells that are resistant to chemotherapy drugs. Using two different chemotherapy drugs decreases the likelihood that some cancer cells would be resistant to the chemotherapy treatment.

6. If the evolution continued for an additional 10 generations, which cancer cell player do you think is most likely to survive and reproduce? Support your choice using your knowledge of cancer biology and information from the data table. Answers will vary. But students should select a student who has a large number of hallmarks of cancer. Students should support their answer using information from the data table.

7. Some people say that “In the future, scientists will discover a single cause for all types of cancer.” Is this statement true or false? Support your answer with information from the class simulation. Cancer is caused by an accumulation of many mutations that enable cells that are “out of control” to survive and reproduce. There is probably no single gene that enables cancer cells to survive and reproduce to form a tumor. “Fit” cancer cells need to have many of the hallmarks of cancer.