15.1 Cancer Biology I

Question 1

Why are cells that cause cancer not recognized by the immune syste?

Answer 1

b/c cells that cause cancer are our own cells.

Question 2

Cancer cells are relatively normal w/one exception. What is the exception?

Answer 2

The exception is that the cells no longer respond to external and internal cues that limit cell division.

Question 3

Which organs have a higher rate of cancer production? Why?

Answer 3

Organs that have epithelial tissues including digestive, respiratory, and reproduction tissue have a higher rate of cancer production

This is b/c cells in these tissues are already programmed to divide over and over again so it only takes a small number of changes for the cells to become cancerous.

Question 4

Which cells rarely become cancerous?

Answer 4

cells that divide infrequently, including muscle and nerve cells become cancerous very rarely.

Question 5

Although skin cancer divides frequently, why are incidents not as high as other cancer cells that divide frequently?

Answer 5

the incidence of skin cancer is low b/c changes to skin cells are easily detected before cells actually become truly cancerous. This makes the point that early detection is an essential part of avoiding cancer.

Question 6

What is a benign tumor?

Answer 6

tumors are benign if they are contained in a discrete location. For epithelial cells tumors are benign if they have not crossed their basement membrane.

Question 7

When is a tumor considered malignant?

Answer 7

Once cells begin to leave the area of origin (aka they start to spread)

Question 8

What is metastases?

Answer 8

tumors that form in places other than the site of origin.

Question 9

How are metastases formed?

Answer 9

a malignant tumor may or may not produce metastases but malignancy is a prerequisite for metastasis.

Question 10

Apart from malignancy, what other factors are necessary for metastases?

Answer 10

the ability of cancer cells to become attached to a new location and thrive in that new location.

Question 11

How are malignant and non-malignant cancers named?

Answer 11

based on the tissues of origin. For ex: carcinomas are malignant tumors of epithelial origins.

Question 12

What is sarcomas?

Answer 12

malignant tumor of connective tissue or muscle origin

Question 13

What is a chondroma?

Answer 13

a benign tumor in cartilage

Question 14

What is leukemia or lymphomas?

Answer 14

Cancer that form in the blood cells

Question 15

What is chondrosarcoma?

Answer 15

malignant cancer formed from cartilage

Question 16

What is adenoma?

Answer 16

benign tumor formed in adrenal

Question 17

What is melanoma?

Answer 17

benign tumor in pigment

Question 18

How does cancer arise?

Answer 18

from a single cell through a process that mimics evolutionary process.

Question 19

What evidence indicates that many cancers will develop from a single cell?

Answer 19

1) Leukemia called chronic myelogenous leukemia is caused by a breakage and reorganization of chromosome 9 and 22, producing very short chromosome called Philadelphia chromosome
2) The analysis of X-chromosomes in female patients.
3) examining morphology of tissues that frequently develop cancers

Question 20

How does myelogenous leukemia indicate evidence that many cancers develop from one single cell?

Answer 20

myelogenous leukemia is caused by a breakage and reorganization of chromosome 9 and 22, producing very short chromosome called Philadelphia chromosome

The breakage occurs in a single characteristic area of these chromosomes, but thee region is hundreds of nucleotides large. When cancer cells from one patient are sequences all of the cells show the break at exactly the same place. However, when cancer cells from different patients are compared small differences are seen. This indicates that these chromosomes have a weak spot, but that the cancer cells in one patient are all probably clones of each other.

Question 21

How does analysis of x-chromosomes in female patients indicate that many cancers will develop from a single cell?

Answer 21

Females have two x-chromosomes. One maternal and one from paternal parent. Staining methods can be used to identify which chromosomes is which. In somatic cells in females one or the other x chromosome is randomly inactivated and you can see this using different staining methods. When tumors from female patients are analyzed, it can be seen that all the tumor cells have the same X chromosome inactivated. Whereas if you look at cells in the body they will randomly be inactivated so that one cell will have the parental X chromosome inactivated and the other will have the maternal chromosome inactivated. So this supports that all cells of a tumor are clones of a single original cell.

Question 22

What can increase your chances of developing cancer?

Answer 22

more exposure to industrial carcinogens

Question 23

what evidence suggest that cancer cells evolve?

Answer 23

If exposed to an industrial carcinogen, the longer you wait after the exposure the more likely cancer develops.

Precancerous cells are around for a long time until some other event occurs to make them fully cancerous.

Question 24

What is the relationship between time and cancer development.

Answer 24

The probability of getting cancer as a function of age is not linear but instead rises very rapidly after the age of 40. This suggest that cells start along the path of becoming cancer cells but it takes time for this to happen and several events must occur before a cell becomes cancerous.

Question 25

How does cancer start?

Answer 25

a single cell must obtain a single mutation. this cell must multiply one of its progeny to obtain a second mutation. The process can continue until one of the cells develops sufficient mutations to allow the development of a cancer.

Question 26

What allows the progress from abnormal cell to fully malignant states?

Answer 26

the genetical instability of cancer cells. when cells display a karytope ( chromosome rearrangement) they are said to be genetically unstable and it is easy to see that this would facilitate the process of a cell obtaining additional mutations toward becoming fully cancerous.

Question 27

What percent of cells that are found in a tumor can actually produce another tumor if transplanted to another site in the body?

Answer 27

1%

Question 28

What are the two mechanisms that cancer stem cells are thought to be generated by?

Answer 28

1) mutation to an existing stem cell in some way that leads it to become a cancer cell.
ex: epithelial tissue since they have many stem cell
2) if a normal somatic cell acquires the necessary characteristics to become a cancer stem cell through a series of mutations

Question 29

What are the steps in metastasis?

Answer 29

metastasis is the process of cancer cells being produced in one place and moving to another place in the body where they produce another tumor.

1) Break free from site of origin (must adhere to the vascular and leave through this system)
2) colonize a distant site
3) proliferation at distant site
4) Angiogenesis (form new blood supply) required for colonization

Question 30

Why is bone tissue more permissive than other environments for cancer growth?

Answer 30

b/c bone marrow is a source of blood, which is needed for cell growth and provide a nurturing environment for many cell types.

Question 31

What kind of environment is needed for a cell to metastasize?

Answer 31

an area that can provide the cell a way to recruit new blood vessels into a tumor.

Question 32

What is angiogenesis?

Answer 32

the process of forming a new blood supply nework

Question 33

Summary of cancer cell properties

Answer 33

 They are more self sufficient than normal cells for growth and proliferation
 They are relatively insensitive to anti-proliferative signals
 They are less prone than normal cells to undergo apoptosis
 They are defective in intracellular control mechanism that limit cell division
 They induce help from normal cells in their environment
 They induce angiogenesis
 They escape from their home tissues and survive at foreign sites
 They are genetically unstable
 They either produce telomerase or acquire some way of stabilizing telomeres

Question 34

What are carcinogens? What is another name for carcinogen?

Answer 34

Chemical agents that cause cancer are carcinogens and are also called cancer initiators

Question 35

What type of compounds can contribute to the formation of cancer? What is an example?

Answer 35

compounds that affect the structure of DNA in cells.

EX: aflotoxin; a toxin produced by certain types of fungi growing on peanuts and other types of grains and its a source of concern about things like peanut butter. Aflotoxin itself does not cause cancer, but one of its metabolic break down products that is produced in the liver during detoxification does.

Question 36

What is a method that can be used to identify carcinogens/cancer initiators

Answer 36

The Ames test.

A special stain of bacteria is grown and exposed to a test agent. The bacteria have a genetic alteration that results in the bacteria being unable to synthesize histidine, which is an essential amino acid. However, additional mutations can reverse the effects of the histidine deficit. When the bacteria are exposed to a carcinogen any mutation that allows the bacteria to grow in a histidine deficient environment can be detected. Often the exposure is carried out in the presence of liver enzyme extracts in an effort to mimic the effects of the liver on potential carcinogens

Question 37

Carcinogen vinyl chloride can lead to

Answer 37

liver angiosarcoma

Question 38

carcinogen benzene can lead to?

Answer 38

acute leukemias

Question 39

carcinogen arsenic can lead to

Answer 39

skin carcinomas, bladder cancer

Question 40

carcinogen asbestos can lead to

Answer 40

mesothelioma

Question 41

carcinogen radium can lead to

Answer 41

osteosarcoma

Question 42

What is the difference between a tumor initiator and a tumor promoter?

Answer 42

Tumor initiators are compounds that directly cause changes to the cells genetic material or can otherwise result in inheritable genetic change such that a cells progeny are also cancerous.

Tumor promoters are agents that make cells misbehave often leading to more aggressive tumor growth, but they are not in of themselves capable of causing cancer.

Question 43

What is one way tumor promoters can alter cell behavior to lead to increased chances of becoming fully cancerous?

Answer 43

a tumor promoter can cause rapid cell division and the large number of precancerous cells increase the chance that one of them will eventually become fully cancerous.

Question 44

Exposure to a tumor promoter in the absence of a tumor initiator will have what kind of effect?

Answer 44

no lasting effect, b/c tumor promoters don’t have lasting effects or create inherited changes to cells.

Question 45

What biological agents can cause cancer?

Answer 45

Virus and bacteria. In addition to directly introducing mutated genes into target cells, they can have other effects that promote cancer. For example, chronic infection or inflammation has also been shown to contribute to cancer development, b/c the response of cells to those events include proliferation

Question 46

What type of virus cause cancer?

Answer 46

DNA viruses like

1) papovavirus -uterine/cervical cancer
2) Hepadnavirus - liver cancer

3) herpesvirus - nasopharyngeal or cancer of lymphocytes

RNA viruses

1) retrovirus - t cells
2) HIV