20.1 The Development and Causes of Cancer

Question 1

any abnormal proliferation of cells

Answer 1

tumor

Question 2

tumors that remain confined to original location; they do not invade surrounding normal tissue or spread to distant body sites

Answer 2

benign tumors

Question 3

tumors that invade surrounding normal tissue and spread throughout the body via circulatory or lymphatic systems; the only tumors properly referred to as cancer

Answer 3

malignant tumors

Question 4

most cancers are in 3 main groups:

Answer 4

1. carcinomas
2. sarcomas
3. leukemias and lymphomas

Question 5

malignancies of epithelial cells; comprise about 90% of human cancers

Answer 5

carcinomas

Question 6

solid tumors of connective tissue (e.g. muscle, bone, cartilage, and fibrous tissue); rare in humans

Answer 6

sarcomas

Question 7

arise from malignancies in blood-forming cells

Answer 7

leukemias

Question 8

arise from malignancies in immune system cells

Answer 8

lymphomas

Question 9

tumors develop from single cells that begin to proliferate abnormally; fundamental feature of cancer

Answer 9

tumor clonality

Question 10

development of cancer is a multistep process; cells gradually become more malignant through a ()

Answer 10

progressive series of alterations

Question 11

at the cellular level, development of cancer is a multistep process:

Answer 11

1. mutation and selection for cells with progressively increasing capacity for proliferation
2. survival of cancer cells
3. invasion of cancer cells into neighboring tissue
4. metastasis

Question 12

mutation leads to abnormal proliferation of a single cells → grows into a population of clonal tumor cells

Answer 12

tumor initiation

Question 13

additional mutations occur within cells of the tumor population

Answer 13

tumor progression

Question 14

cancer cells are () → high frequency of mutations and chromosome abnormalities

Answer 14

genetically unstable

Question 15

process of mutations conferring selective advantages to cancer cells (primarily rapid growth) → descendants of mutated tumor cells become dominant

Answer 15

clonal selection

Question 16

clonal selection continues throughout tumor development → cells with () become more dominant

Answer 16

more mutations

Question 17

studies of () provide a clear example of tumor progression during the development of a common human malignant tumor

Answer 17

colon carcinomas

Question 18

overview of colon carcinoma development

Answer 18

1. earliest stage of tumor development: increased proliferation of colon epithelial cells
2. one of the cells in the proliferating population gives rise to a small benign neoplasm called an adenoma or polyp
3. further rounds of clonal selection lead to growth of adenomas
4. invasion of tumor cells into the underlying connective tissues indicates malignant carcinomas arising from benign polyps
5. eventually, cancer cells penetrate the colon walls and metastasize to other abdominal organs, blood, and lymphatic vessels

Question 19

characteristic properties of cancer cells that distinguish them from normal cells and contribute to malignancy:

Answer 19

1. uncontrolled proliferation
2. secretion of growth factors
3. reduced cell adhesion molecules
4. secretion of proteases
5. promotion of angiogenesis
6. abnormal differentiation
7. failure to undergo apoptosis
8. capacity for unlimited replication

Question 20

in culture, normal cells display density-dependent inhibition, which allows them to

Answer 20

proliferate until they reach a finite cell density (partly determined by growth factor availability), after which they enter G0

Question 21

normal fibroblast cells show contact inhibition, allowing them to ()

Answer 21

proliferate across a culture dish until they make contact with neighboring cells

Question 22

ceasing of normal fibroblast proliferation upon cell-cell contact results in the formation of an ()

Answer 22

orderly array of cells on the dish

Question 23

because cancer cells do not display density-dependent inhibition or contact inhibition, they ()

Answer 23

grow to high densities in culture and do so in disordered, multilayered patterns

Question 24

cancer cells produce growth factors that stimulate their own proliferation: ()

Answer 24

autocrine growth stimulation

Question 25

reduced growth factor dependence of cancer cells can also result from ()

Answer 25

abnormalities in intracellular signaling systems

Question 26

most cancer cells are less adhesive than normal cells due to ()

Answer 26

reduced expression of cell surface adhesion molecules

Question 27

loss of () is important in development of carcinomas

Answer 27

E-cadherin

Question 28

why do cancer cells secrete proteases

Answer 28

proteases digest EC matrix components (e.g. collagen), allowing them to invade adjacent normal tissues

Question 29

why do cancer cells promote angiogenesis

Answer 29

• new blood vessels deliver more oxygen and nutrients that contribute to tumor growth
• new capilliaries are also easily penetrated by tumor cells, contributing to metastasis

Question 30

why do cancer cells promote abnormal differentiation

Answer 30

if cells are blocked at an early stage of differentiation, they can continually proliferate

Question 31

growth of some tumors is driven by the proliferation of a () → produces more stem cells and differentiated tumor cells that lack the potential for continual self-renewal

Answer 31

subpopulation of cancer stem cells

Question 32

DNA damage in cancer cells does not trigger apoptosis, allowing them to be ()

Answer 32

resistant to irradiation and chemotherapeutic drugs (act by damaging DNA)

Question 33

cancer cells express high levels of (), allowing them to maintain chromosome ends for an indefinite number of divisions

Answer 33

telomerase

Question 34

normal cells have limited amounts of telomerase and gradually lose telomeres → leads to ()

Answer 34

cessation of replication

Question 35

conversion of normal cells to tumor cells

Answer 35

cell transformation

Question 36

substances that cause cancer by acting to damage DNA and induce mutations

Answer 36

carcinogens

Question 37

examples of carcinogens

Answer 37

1. solar UV radiation
2. aflatoxin
3. benzo(alpha)pyrene, dimethylnitrosamine, nickel compounds (found in tobacco smoke)

Question 38

other carcinogens are () that stimulate cell proliferation

Answer 38

tumor promoters

Question 39

examples of tumor promoters

Answer 39

1. asbestos
2. Heliobacter pylori
3. some viruses

Question 40

how do tumor viruses directly cause cancer in humans or animals

Answer 40

they deliver genes that trigger tumor formation and progression (cancer)

Question 41

fundamental abnormality of cancer: ()

Answer 41

continual unregulated proliferation of cancer cells

Question 42

proliferation of cancer cells causes them to spread throughout the body and ()

Answer 42

interfere with function of normal tissues and organs

Question 43

the loss of growth control exhibited by cancer cells is the net result of ()

Answer 43

accumulated abnormalities in multiple cell regulatory systems

Question 44

4 most common cancers:

Answer 44

breast, lung, prostate, colon/rectum