Lesson Plan - NIH Office of Science Education

Cell Biology and Cancertypes of adult cancer, provided additional support for the hypothesisof multistep carcinogenesis. In fact, one of the goals of research todayis to identify each of the steps and genes involved in the long and complex succession of events that occurs to create the malignant growth ofcancer cells.Whereas Activity 2 illustrates the contributionthat cell biologists andgeneticists have made tounderstanding cancer,Activity 3 illustrates thecontribution that epidemiologists have made.One of the most excitingaspects of cancerresearch in recent yearshas been the construction of an understandingof cancer that unifies thework of many types ofscientists studying cancer for more than 100years.Note that this question returns students to the challenge they weregiven in Step 4.17. Challenge your students to evaluate the models they used to test the differenthypotheses for the development of cancer (that is, to think aboutthe ways in which the random number table exercise and the CD-ROMbasedsimulation do and do not match reality).Remind students that all models are inaccurate in some respects. Forexample, the mutational events within cells may not be completely random, as the models assume. The models also assume that the probability of each individual mutational event is the same, and this may notbe the case. There is some evidence, for example, that some mutationsincrease the probability that other mutations will occur. In addition, themodels do not consider that some mutations may be detected andrepaired. Nevertheless, the fact that the models the students used arenot perfect does not mean they are not useful tools for understandinghow disease processes work.18. Close the activity by distributing one copy of Master 3.6, Testing anExplanation by Looking at Additional Data. Ask students to use theirunderstanding of cancer as a multistep process to explain each of theobservations listed.Question 1 Cancer is a disease of aging.The questions on Testingan Explanation are challenging, but they represent an excellent opportunity for you toevaluate your students’understanding of theactivity’s major conceptsand their ability to applytheir understanding tonovel situations.Students should be able to explain it takes time for all of the mutations involved in the development of cancer to accumulate, and thatthis explains why the incidence of cancer increases with age (that is,why cancer is more likely to “strike” in the middle or later years thanin childhood, youth, or young adulthood.Question 2 You’ve come a long way, baby.Students should be able to explain that as these women began tosmoke, they began to accumulate cancer-causing mutations in theirlung cells. Because the accumulation of these mutations to the pointwhere a cell becomes cancerous takes time, the results of theincrease in the number of women smoking (in the form of anincrease in lung cancer among women) did not begin to appear for20 to 25 years.Question 3 Genes and increased susceptibility.Students should recognize that if a person is born with a cancercausingmutation already present in his or her cells, he or she has62