Download Chapter 11 Cancer Taken collectively, cancer is the leading cause

Chapter 11
Cancer
Taken collectively, cancer is the leading cause of death in the U.S.
Statistically, nearly 1 in 3 of us will develop cancer during our lifetime
Cancer is not a single disease
We classify any disease that is caused by uncontrolled cell division as cancer
regardless of which cell type is affected
The cell cycle is normally very tightly regulated
Cancerous cells have several unique properties that distinguish them from normal cells of
the same type
 They are not subject to “contact inhibition”
 They can divide indefinitely
 At the ends of chromosomes are highly repetitive sequences making up telomeres
 Everytime a chromosome is replicated during cell division, the telomere becomes
shorter
 Eventually, the shortened telomere signals that that cell should no longer divide
 Cancer cells produce the protein telomerase that prevents the telomeres from
shortening
 They move through the cell cycle despite normal “stop” signals and without the need
for “go” signals
Tumor suppressor genes and proto-oncogenes
 Tumor suppressor genes act as brakes in the cell cycle, preventing defective cells
from progressing through the cell cycle
Proto-oncogenes are normal cellular genes that act as pushing on the gas pedal, only
applied when the cell is cleared to progress through the cell cycle
Oncogenes are mutated versions of proto-oncogenes, always pushing on the gas pedal
 One crucial tumor suppressor is p53
o
It promotes programmed cell death (apoptosis) in pre-cancerous and
cancerous cells
o
Loss of p53 function has been implicated in cancers in many different
types of cells
The progression of cancer
 Cancers progress in stages, requiring mutations along the way
 Proto-oncogenes ➔oncogenes
 Loss of tumor suppressors
The 3 phases in the development of cancer cells
 Initiation – a single cell undergoes a mutation that causes it to divide repeatedly
 Promotion – a tumor develops and cells within the tumor mutate
 Progression – a cell mutates in such a way that allows it to invade surrounding tissue
Angiogenesis and metastasis
 Angiogenesis - formation of new blood vessels to supply nutrients and oxygen to the
tumor
 Metastasis - cells move into the bloodstream or lymphatic vessels to make new
tumors at sites distant from the primary tumor
Causes of cancer
 Genetics
 Environmental carcinogens
 Radiation exposure
 Environmental carcinogens (tobacco smoke and pollutants)
 Viruses
 Diet
Genetic causes of cancer
 Examples of genes associated with cancer
o
BRCA1 and BRCA2 – tumor suppressor genes that are associated with
breast cancer
o
RB – a tumor suppressor gene that is associated with an eye tumor
o
RET – proto-oncogene that is associated with thyroid cancer
 Mutations of these genes predispose individuals to certain cancers but it takes at
least one more acquired mutation during their lifetime to develop cancer
Environmental causes of cancer
 Cancer researchers have estimated that >50% of all cancers are caused by
environmental carcinogens
 Radiation
o
Environmental factors such as UV-B light (in sunlight or tanning lights)
and x-rays can cause mutations in DNA
 Organic chemicals
o
Tobacco smoke (N-nitrosonornicotine, vinyl chloride, benzo[a]pyrene,
and others) increases cancer of lungs, mouth, larynx, and other sites
o
Pollutants - substances such as metals, dust, chemicals, and pesticides that
increase the risk of cancer
 Viruses
o
Hepatitis B & C viruses that can cause liver cancer
o
Epstein-Barr virus - can cause Hodgkin’s and non-Hodgkin’s lymphoma
o
Human papillomavirus - can cause cervical cancer
 Diet
o
Obesity has been linked with a >50% increased risk of colon cancer in
both men and women and a >50% in the risk of breast and uterine cancer in
women
o
Diets high in animal fat have been associated with an increased risk of
colon cancer
o
Extensive alcohol consumption has been associated with increased risk of
certain cancers, in particular in the mouth, throat, and esophagus

On the other hand, certain foods may lower the risk of developing cancer

Green, leafy vegetables contain high levels of beta-carotene, easily
converted to vitamin A, an antioxidant

Vitamin C also acts as an antioxidant
Types of cancer
 Oncology – study of cancer
 Carcinomas - cancers of the epithelial tissues
 Adenomas - cancers of glandular tissues
 Adenocarcinomas - cancers of glandular epithelial cells
 Sarcomas - cancers of muscular and connective tissues
 Blastomas - cancers of embryonic tissues
 Leukemias - cancers of the blood
 Lymphomas - cancers of lymphatic tissues
Seven warning signs of cancer
 Change in bowel or bladder habits
 A sore that does not heal
 Unusual bleeding or discharge
 Thickening or lump in breast or elsewhere
 Indigestion or difficulty in swallowing
 Obvious change in wart or mole
 Nagging cough or hoarseness
Some routine cancer screening tests
 Self-examination – monthly exams of breasts and testicles starting at age 20
 Colonoscopy – every 5 years starting at age 50
 Pap smear – should begin 3 years after vaginal intercourse or no later than age 21
 Mammogram – yearly after age 40
Detecting skin cancer
A – asymmetry
B – border is irregular
C – color varies from one area to another
D – diameter is larger than 6 mm
Other ways to detect cancer
 Tumor marker tests – blood tests for tumor antigens/antibodies
 CEA (carcinoembryonic antigen) antigen can be detected in someone with colon
cancer
 PSA (prostate-specific antigen) test for prostate cancer
 Genetic tests – tests for mutations in proto-oncogenes and tumor-suppressor genes
 RET gene (thyroid cancer)
 P16 gene (associated with melanoma)
 BRCA1 (breast cancer)
 A diagnosis of cancer can be confirmed by performing a biopsy
Standard cancer treatments
 Surgery – removal of small cancers
 Radiation therapy – localized therapy that causes chromosomal breakage and
disrupts the cell cycle
 Chemotherapy – drugs that treat the whole body that kill cells by damaging their
DNA or interfering with DNA synthesis
 Bone marrow transplants – transplant bone marrow from one individual to another
Newer cancer therapies
 Immunotherapy – inject immune cells that are genetically engineered to present the
tumor’s antigens
 Passive immunotherapy – antibodies against tumor antigens that are linked to
radioactive isotopes or chemotherapeutic drugs are injected into the body
 p53 gene therapy – a retrovirus that is injected into the body where it will infect and
kill only tumor cells (cells that lack p53 = tumor cells)
 Angiogenesis inhibition - Angiostatin and endostatin are drugs in clinical trials that
appear to inhibit angiogenesis