Etiology of cancer

May 7, 2020 etiology of cancer 1

SEMINAR
ON
ETIOLOGY OF CANCER
SUBMITTED BY: IRENE THAKURIA
Msc (N) 2ND YEAR
F.M.C.O.N
May 7, 2020 2etiology of cancer

SPECIFIC OBJECTIVES
1. What is cancer?
2. Definition of carcinogenesis
3. Theories of carcinogenesis
4. Process of carcinogenesis
5. Etiological and risk factors of cancer
 Biological carcinogenesis
 Chemical carcinogenesis
 Physical carcinogenesis

 Radiation carcinogenesis
 Hormonal carcinogenesis
 Viral carcinogenesis
 Dietary factors
 Emotional factors
 Environmental factors

CANCER
•An abnormal growth of cells which tend
to proliferate in an uncontrolled way
and, in some cases, to metastasize
(spread) - WHO
• Cancer is not a single disease.
Each specific cancer occurs through
mutations in specific genes

CARCINOGENESIS
Carcinogenesis or oncogenesis or tumorigenesis
means mechanism of induction of tumors. Agents
which can induce tumor are called carcinogens.
Carcinogenesis is the process by which normal cells
are transformed into cancer cells.
The process begins when a single cell- the clonal
cell – that has sustained genetic change.
Malignant transformation results when a normal
appearance and funcion changes into a cell with
malignant characteristics.

CARCINOGENS

•CARCINOGENS are a group of substances
that are directly responsible for damaging
DNA, promoting or aiding cancer.
•When our bodies are exposed to
carcinogens, FREE RADICALS are formed and
try to steal electrons from other molecules in
the body. These free radicals damage cells and
affect their ability to function normally.

•Recent evidence suggests that
carcinogenesis is a multistep process
and involves a number of genetic
mutations that cause progressive
transformation of normal cells into
highly malignant deriveratives.

GENE MUTATION THEORY:

According to the Gene ( somatic) mutation theory, cancer is
a genetic disease caused by mutation of genes.
Genes control disease and NOTHING CONTROLS GENES.
Central dogma of molecular biology
Genes create protein and protein does not control gene.
MECHANISM:
Genes are the blueprint of the metabolism(phenotype).
They exist in a kind of bunker which does not let any
metabolic signals in.
Genes are stable and only randomly change when hit by a
photon.
 In summary, according to the GMT, genome is an isolated
and closed system of non interacting stable genes

INCEPTION:
Cancer starts when a photon
breaks a gene, which is called
gene mutation. Eight such
random hits control cancer
progression.
CARCINOGENESIS:
It is possible to speed up tumor
progression by irridating the cell.
Photons break many genes and
tumor grows faster.

.
•It is the most widely accepted and is supported by a
large volume of experimental data.
• However, it does not explain tumor heterogeneity
and aneuploidy and also the long latent
periods between exposure to carcinogens and the
development of tumors.

ANEUPLOIDY THEORY
• Aneuploidy is the second
major category
of chromosome mutations
in which chromosome
number is abnormal.
• Aneuploids can have a
chromosome number
either greater or smaller
than that of the wild type.
• For eg: a human cell having 45
or 47 chromosomes instead of
usual 46.May 7, 2020 14etiology of cancer

ANEUPLOIDY THEORY
• Aneuploidy drives two hallmarks of cancer:
Cell proliferation and
Evasion of the immune system.
Aneuploidy promotes cell proliferation and
inhibits the infiltration of immune cells
leading to immune invasion. Melanoma
patients with high aneuploidy show poorer
responses to immunotherapy with anti-CTLA 4
antibodies.

•According to this hypothesis, a carcinogen
initiates carcinogenesis by a preneoplastic
aneuploidy, which destabilizes mitosis.
• This initiates an autocatalytic karyotype
evolution that generates new chromosomal
variants, including rare neoplastic .
•The aneuploidy hypothesis provides a plausible
explanation for the long latent periods from
carcinogen treatment to cancer development and
the clonality.

EPIGENETIC THEORY

• In biology, epigenetics
is the study of
heritable phenotype
changes that do not
involve alterations in
the DNA sequence.

EPIGENETIC THEORY:
Increased levels of methylated cytosine
(one of the pyrimidine bases in DNA)
results in the elevation of
spontaneous mutation rates in the
affected genome.May 7, 2020 20etiology of cancer

BERENBLUM AND SHUBIK
THEORY(1947)

PROCESS

INITIATION
 IT is the 1st step in cancer development.
Occurs at gene level, in which a change in
the cells genetic material primes the cell to
become cancerous.
Initiators such as tobacco, chemicals,
viruses, radiation, biologic agents alter
normal enzymatic mechanisms and alter
the gene structure of the cellular DNA.

Initiation is the direct exposure to DNA to a
carcinogen, resulting in irreversible changes
that permits malignant transformation.
To become initiated cell, the carcinogens
exposure must alter cellular DNA structure---
causing one or more breaks in the DNA chain,
eliminating a genetic component resulting in
faulty DNA repair .

PROMOTION
 The second and final step in the
development of cancer is promotion.
Once a normal cell is initiated and become a
cancer cell, growth enhancement can allow it
to form a tumor.
During promotion, repeated exposure to
promoting eg: ionizing radiation can cause
various cancer particularly sarcomas,
leukemia, thyrois ca and breast ca.

PROGRESSION
Here cellular changes formed during initiation and
promotion now exhibit malignant behaviour. These
cells show capacity to invade or metastasize
surrounding tissues.
The initiated cells proliferate causing a fast increase in
tumor size. As tumor grows in size, cells undergo
mutations leading to increasing heterogeneity of the
cell population

Agents that cause promotion or promotes maybe
substances in the environment such as chemicals,
drugs(barbiturates) and hormones. In order for a tumor
to form, initiation must be followed by promotion.
In early growth, tumor receives blood supply from
diffusion from surrounding tissues but when tumor
reaches more than 1-2 mm diameter, blood supply
through diffusion is insufficient , so tumor notes TAF
(Tumor Angiogenesis Factor).
 This causes capillaries and blood vessels develop
branches into tumor and supply nourishment.

METASTASIS

As the tumor progression advances, the cells
lose their adherence property, detach from the
tumor mass and invade the neighboring tissues.
The detached cells also enter the circulating blood
and lymph and are transported to other
organs/tissues away from the site of the primary
growth and develop into secondary tumors at the
new sites.
These form the distant metastases, resulting
in widely spread cancers.

METASTATIC MECHANISMS
 The detached cells enter the circulating blood and lymph and are
transported to other organs/ tissues away from the site of the 1˚
growth and develop into 2˚ tumors at the new sites.
A)LYMPHATIC SPREAD
B)HEMATOGENOUS SPREAD
The progress of the neoplastic disease depends on metastatic
changes that facilitate:
(a)invasion of local normal tissues,
(b) entry and transit of neoplastic cells in the blood and
lymphatic systems, and
(c) the subsequent establishment of secondary tumor growth at
distant sites.

ETIOLOGICAL AND RISK FACTORS
BIOLOGICAL CARCINOGENESIS
CHEMICAL CARCINOGENESIS
PHYSICAL CARCINOGENESIS
RADIATION CARCINOGENESIS
HORMONAL FACTORS
VIRAL CARCINOGENESIS
DIETARY FACTORS
EMOTIONAL FACTORS
ENVIRONMENTAL FACTORS

BIOLOGICAL CARCINOGENESIS
AGE  HORMONAL STATUS

FAMILY HISTORY
GENETIC
PREDISPOSITION

PARASITES FUNGUS
Eg: SCHISTOSOMA
HAEMATOBIUM- urinary
bladder- squamous cell
carcinoma
ASPERGILLUS FLAVUS GROWS IN
STORED GRAINS, and liberates
AFLATOXIN HEPATOCELLULAR
CARCINOMAMay 7, 2020 35etiology of cancer

BACTERIA
H. PYLORI COLONIZES
GASTRIC MUCOSA –
CHRONIC GASTRITIS
AND PEPTIC ULCER-
PROLONGED
INFECTION- GATRIC
LYMPHOMA / GASTRIC
CARCINOMA

CHEMICAL CARCINOGENESIS

In 1775, an English physician, PERCIVAL POTT
observed the high incidence of cancer of the scrotum
in chimney sweeps was due to exposure to coal tars.
Century later scientists in Germany found high
incidence of bladder cancer among workers
exposed to aromatic amines.

Since then, 6 million chemicals have been identified
and registered with the CHEMICALS ABSTRACTS
SERVICE.
HOWEVER, FEWER THAN 1000 of these chemicals
have been examined for their potential to cause
cancer.

KNOWN / SUSPECTED CHEMICAL
CARCINOGENS IN HUMANS
LUNG TOBACCO SMOKE, ARSENIC, ASBESTOS
PLEURA ASBESTOS
ORAL CAVITY TOBACCO SMOKE, ALCOHOL, NICKEL COMPOUNDS
ESOPHAGUS TOBACCO SMOKE, ALCOHOL, SMOKE, SALTED
PICKLED FOODS
COLON HETEROCYCLIC AMINES
LIVER HETEROCYCLIC AMINES
KIDNEY TOBACCO SMOKE, PHENACETIN
PROSTATE CADMIUM
SKIN ARSENIC, COAL TAR, SOOT, PUVA
BONE MARROW BENZENE, TOBACCO SMOKE, ANTI-NEOPLASTIC
AGENTSMay 7, 2020 40etiology of cancer

CATEGORIES OF CHEMICAL
CARCINOGENESIS
• DIRECT ACTING
CHEMICAL
CARCINOGENS do not
require metabolic
activation and
conversion to become
carcinogenic.
• Eg: busulfan, nitrogen
mustard
• INDIRECT ACTING
CHEMICAL
CARCINOGENS require
METABOLIC activation
to become
carcinogenic.
• Eg: coal tar products,
smoking, alcohol

CARCINOGEN TUMOR
DIRECTACTINGCHEMICAL
CARCINOGENS
1)ALKYLATING AGENTS
2)a) Anti- cancer drugs(
eg:cyclophosphamide,
chloraambucil,
busulfan)
b) Beta- propiolactone
c) EPOXIDES
LYMPHOMAS
AML
BLADDER CANCER

INDIRECT ACTING CHEMICAL
CARCINOGENS (PROCARCINOGENS)
1) Polycyclic, aromatic hydrocarbons( in
tobacco, smoke, fossil fuel, soot, mineral
oil, smoked animal foods, industrial and
atmospheric pollutants)
 LUNG CANCER
 SKIN CANCER
 CA OF UPPER AERODIGESTIVE TRACT
2) AROMATIC AMINES AND AZO-DYES:
a) Beta- naphthylamine
b) Benzidine
c) Azo-dyes
BLADDER CA
HEPATOCELLULAR CA
3)NATURALLY OCCURING PRODUCTS: HEPATOCELLULAR CA
a) Mitomycin C
b) Betel nuts

PHYSICAL CARCINOGENESIS

PHYSICAL CARCINOGENESIS
RADIATION NON-RADIATION
IONIZING
RADIATION
NON- IONIZING
RADIATION

IONIZING RADIATION- X-rays,
electrons, protons
Occupational exposure
Radiologists, nuclear workers, radiation
technologists, medical exposure-
diagnostic chest X-rays, mammography,
MRI
Greater risk when exposed at younger
age

NON- IONIZING RADIATION
UV rays – known to cause skin cancer
Xeroderma pigmentosum and COCKAYNE’S
SYNDROME have increased risk due to
defective nucleotide excision repair.
Mechanism of carcinogenesis is due to the
formation of dimers between adjacent
pyramids in DNA
Eg: cyclobutane dimer

Eg: cyclobutane dimer

Xeroderma pigmentosum

Cockayne syndrome
• Cockayne syndrome is a
rare disorder characterized
by an abnormally small
head size (microcephaly), a
failure to gain weight and
grow at the expected rate
(failure to thrive) leading to
very short stature, and
delayed development.

NON-RADIATION PHYSICAL AGENT
These are the various forms of injury and are
less important.
Eg: Noise, Vibration, Optical Radiation and
Electromagnetic Fields

RADIATION CARCINOGENESIS

RADIATION CARCINOGENESIS
UV light and ionizing radiation are the two
main forms of radiation carcinogens which can
induce cancer.
A property common between the two forms
of radiation carcinogens is the appearance of
mutation followed by long period of latency
after initial exposure
Often after 10-20 years or even later.

HORMONAL CARCINOGENESIS

 ENDOGENOUS HORMONES- ca
breast, ovary, endometrium in
females; ca prostate, testis in males.
 Prolonged stiulation- Neoplasia
 Eg: a direct carcinogenic effect of
estrogen is known from the
occurance of vaginal and cervical
clear cell carcinomas in girls born of
mothers having been teated with
DIETHYLSTILBESTEROL during
pregnancy.

VIRAL CARCINOGENESIS
It has been estimated that 20% of all cancers
worldwide are due to persistent virus infection.
Viruses capable of inducing tumors in
experimental animals :
VIRUS ASSOCIATE TUMOR
HPV •CERVICAL CA, SQUAMOUS CELL CARCINOMA
AT OTHER SITES
PAPILLOMA VIRUSES •PAPILLOMAS(WARTS)
•ALIMENTARY TRACT CANCER

EPSTEIN BARR VIRUS NASOPHARYNGEAL CA
BURKITT LYMPHOMA
HUMAN HERPES VIRUS
8
PLEURAL EFFUSION
ADENOVIORUSES SARCOMAS
HEPATITIS B
RNA VIRUS
HEPATOCELLULAR CA

DIETARY CARCINOGENS

A) Naturally occuring dietary carcinogens:
1. NATURAL PESTICIDES: Allyl isothiolynate in
cabbage, cauliflower, hydrazines in
mushrooms and pyrrolidine in herbal tea.
2. MYCOTOXINS: Alfatoxins in corn, peanut and
ochratoxins in grains

B) PRODUCTS OF FOOD PREPARATION AND
PROCESSING:
URETHENE in all fermented foods,
heterocyclic aromatic amines in barbecued
chicken, nitroso compounds in cured meats
and diary cheese products.
C) SYNTHETIC CARCINOGENS IN
DIET(ADDITIVES)
Sweetners, colorants flavourants

EMOTIONAL FACTOTS

ENVIRONMENTAL FACTORS:

• LIFESTYLE FACTORS:
ALCOHOL
SMOKING – Due to presence of benzpyrene
and N-nitrosodimethylene
TRAUMA AND INFLAMMATION

RESEARCH ARTICLE
• World J Clin Oncol. 2016 Feb 10; 7(1): 54–86.
• Published online 2016 Feb
10. doi: 10.5306/wjco.v7.i1.54
• PMCID: PMC4734938
• PMID: 26862491
• Historical review of the causes of cancer
• Clarke Brian Blackadar

Abstract
• In the early 1900s, numerous seminal publications reported
that high rates of cancer occurred in certain occupations.
During this period, work with infectious agents produced
only meager results which seemed irrelevant to humans.
Then in the 1980s ground breaking evidence began to
emerge that a variety of viruses also cause cancer in
humans. There is now sufficient evidence of carcinogenicity
in humans for human T-cell lymphotrophic virus, human
immunodeficiency virus, hepatitis B virus, hepatitis C virus,
human papillomavirus, Epstein-Barr virus, and human
herpes virus 8 according to the International Agency for
Research on Cancer (IARC).

• Many other causes of cancer have also been
identified by the IARC, which include: Sunlight,
tobacco, pharmaceuticals, hormones, alcohol,
parasites, fungi, bacteria, salted fish, wood dust, and
herbs.
• The World Cancer Research Fund and the American
Institute for Cancer Research have determined
additional causes of cancer, which include beta
carotene, red meat, processed meats, low fibre diets,
not breast feeding, obesity, increased adult height
and sedentary lifestyles.

• In brief, a historical review of the discoveries
of the causes of human cancer is presented
with extended discussions of the difficulties
encountered in identifying viral causes of
cancer.

CONCLUSION

REFERENCES
1) Langhorne E. Martha, Fulton S Janet, Otto E Shirley. Oncology
Nursing. 5th ed. St. Louis, Missouri. Mosby;2007
2) Otto E. Shirley. Oncology Nursing. 2nd ed. St Louis, Missouri.
Mosby;1994
3) Desai P. Practical clinical oncology. 5th ed. Jaypee Brothers Ltd;
2007
4) Lewis SL. Medical Surgical Nursing. 7th ed. New Delhi.
mosby,;2007
5) Mehta S. Ram. Oncology Nursing. 1st ed. Jaypee Brothers Medical
publishers(P) Ltd. New Delhi;2007
May 7, 2020 etiology of cancer 70

Etiology of cancer

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