Building a Model of Tumorigenesis: A small group activity for a Cancer

Biology/Cell Biology course

L. K. Wright

Supplemental File : Multistep Tumorigenesis Slides

Human tumorigenesis is a multi-step process.

Human tumor development as a multi-step process has been most clearly documented

in the intestinal epithelium (colon)

Insert diagram of human colon here

http://www.webmd.com/digestive-disorders/picture-of-the-colon

The instructor may want to include images of normal colon vs colon cancer here for a comparison.

Evidence supports the idea of a “pre-cursor---product” relationship

Normal colon epithelium

colon hyperplasia

colon dysplasia

colon adenoma (polyp)

colorectal carcinoma

Evidence #1: Clinical studies of patients who have undergone removal of colon polyps demonstrate lower-than-expected cumulative incidences of colorectal cancer.

Cumulative Incidence of Colorectal Cancer in the National Polyp Study Cohort.

The instructor would show Figure 1 (Cumulative Incidence of Colorectal Cancer in the National Polyp Study Cohort) from

Winawer, S.J., Zauber, A.G., Ho, M.N., O’Brien, M.J., Gottlieb, L.S., Sternberg, S.S., Waye, J.D., Schapiro, M., Bond, J.H., Panish, J.F., et al. (1993). Prevention of Colorectal Cancer by Colonoscopic Polypectomy. N. Engl. J. Med. 329, 1977–1981.

http://www.nejm.org/doi/full/10.1056/NEJM199312303292701

Evidence #2: Nearly 100% of individuals with Familial adenomatous polyposis (FAP) will develop colorectal carcinoma, if not treated.

Familial adenomatous polyposis (FAP)

• FAP is an inherited/familial cancer syndrome.

• People with FAP have a somatic mutation in one copy of the APC (adenomatous polyposis coli) Tumor Suppressor Gene on chromosome 5

• People with FAP present with hundreds of colon polyps (adenomas) by early adulthood.

• 100% of people with FAP will develop colon carcinoma if not treated.

Colon of familial adenomatous polyposis coli patient compared to normal colon. (A) The polyposis colon is completely covered by hundreds of projecting polyps each resembling a tiny cauliflower when viewed with the naked eye. (B) The normal colon wall is a gently undulating but smooth surface. (Courtesy of Andrew Wyllie and Mark Arends.)

Question: What’s the problem with all of these tiny polyps in FAP patients?

Images from:http://www.ncbi.nlm.nih.gov/books/NBK26902/figure/A4344/

One pathway of multi-step

tumorigenesis looks like this

Mutation inactivates tumor suppressor genes

Cells proliferate

Mutation inactivates DNA repair genes

Mutation of proto-oncogene results in an oncogene

Mutation(s) inactivate(s)more tumor suppressor genes

CANCER

NORMAL CELL

What are the genetic

alterations that occur at each

step in the pathway?

Mutation inactivates tumor suppressor genes

Cells proliferate

Mutation inactivates DNA repair genes

Mutation of proto-oncogene results in an oncogene

Mutation(s) inactivate(s)more tumor suppressor genes

CANCER

Think/pair/share

How would you design a study to

uncover the genetic changes that occur

during tumorigenesis of a

specific cancer type?

Mutation inactivates tumor suppressor genes

Cells proliferate

Mutation inactivates DNA repair genes

Mutation of proto-oncogene results in an oncogene

Mutation(s) inactivate(s)more tumor suppressor genes

CANCER

We are going to do an activity based on a paper from The New England Journal of

Medicine entitled:

“Genetic Alterations During Colorectal-Tumor Development”

As part of this activity you will be constructing a scientific model. What is a “scientific model”? Why are they useful?

In the paper tumors are classified as…

Normal epithelium

Early adenoma

Intermediate adenoma

Late adenoma Carcinoma

Class I Class II Class III

= normal cell

= tumor cell

1. Using the data presented in Table 1, calculate the totals and percentage of Class I, Class II, Class III and Carcinoma specimens that are positive for Ras gene mutations.

a. What is a mutation? b. How do you interpret the “Mutation” column in Table 1?

2. According to Table 1, what class (es) of tumors has the highest frequencies of Ras mutations?

3. Analyze the data presented in Table 2. What histopathological feature of adenomas is most highly correlated with Ras mutations?

4. Vogelstein et al. investigated allelic deletions in colorectal tumors at three different chromosomal locations. The data is presented in Table 3. In 1988 the genes of significance located on 5q, 18q, and 17p had not yet been identified. What broad class of genes are most likely located in these regions of chromosome loss? Explain your reasoning.

5. Use the data presented in Tables 1 and 3 to create a figure that shows the percentage of each type of genetic abnormality found in each type of tumor (Class I, Class II, Class III and Carcinoma). Include an appropriate figure description.

6. Based on the data presented in this paper, construct a model of colon tumorigenesis showing where the four genetic alterations (ras mutation, 5q, 18q, and 17p) are most likely located on the pathway.

7. What are scientific models? Explain why scientists create and use scientific models.

This model was published in 1990 (by the same research lab)

5q mutation or loss

FAP

DNA hypo-methylation

Ras mutation

18q loss

17p Lossp53

Other alterations