Defination of Cancer / Tumor, Types of Cancer, Characteristics of Cancer Cells, Hypothesises about Cancer, Tumor Viruses-DNA and RNA tumor viruses, Oncogene theory, Protovirus theory, Provirus Theory
1. By
Dr. G. V. Mali
Department of Microbiology
Bharati Vidyapeeth’s
Matoshri Bayabai Shripatrao Kadam Kanya Mahavidyalaya,
Kadegaon Dist. Sangli
8th September 2018
2. Oncogenesis :
Also termed as ‘Carcinogenesis’ – The process of
formation of Cancer
Cancer- Latin Word – Meaning is Crab.
Greek Physician Hippocrates – Crab like Disease.
Definition – Abnormal , unregulated and uncontrolled
growth of cells – result is lumps or mass of cells
Cancer is also known by the term – Tumor or
Malignancy
Tumor is Latin word- means swelling
Suffix ‘-oma’ is used to describe the Tumor
3. Types of Cancer :
Classification is done on two Criteria
1. Pattern of Growth
i. Benign Tumor ii. Malignant Tumor
2. Types of tissues in which it originates
i. Carcinomas ii. Sarcomas iii. Leukemias iv. Lymphomas
4. i. Benign Tumors -
• Cancer cells do not invade surrounding tissues
• Remain localized as a compact mass
• Encapsulated by a membrane called lamina
• Grow by displacing surrounding tissues
• They are not fatal, however…..
• They are usually removed by surgery
ii. Malignant Tumors -
• Cancer cells invade surrounding tissues, organs & other parts
• Capable of invasion and metastasis
• Not encapsulated by any membrane
• Growth is fast and lethal
• Resistant to treatment and may cause death
5.
6. i. Carcinomas-
• Cancer of epithelial cells , most common
• Accounts for 85 – 90 % of total human cancers
• Skin, prostate , bladder , breast , linings of respiratory,
gastrointestinal , urinary and genital systems
•Two major subtypes-
•Adenocarcinoama-develops in organs and glands
•Squamous cell carcinoma- in sqamous epithelium
ii. Sarcoma -
• Cancer of supportive and connective tissues
• Bones, cartilages, muscles, blood vessels & tissues at joints
• Account for 1 % of total human cancers
• Arms , legs, hands , feet , chest , back , hips , shoulder,
abdomen, head and neck
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9. iii. Leukemias- ( Blood cancer / liquid cancer )
• Cancer of blood forming cells (hematopoietic cells) of bone
marrow
• Accounts for 4% of total human cancers
• Hematopoietic cells produce WBCs
• Characterized by overproduction of abnormal & immature WBCs
• Such cells do not play role in the defense mechanism of body
• Four Types-
i. Acute lymphocytic leukemia(ALL)-Cancer of lymphocytes
ii.Acute myelogenous leukemia ( AML)- Cancer of granulocytes &
monocytes
•Chronic lymphocytic leukemia ( CLL)
•Chronic myelogenous leukemia ( AML)
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13. iv. Lymphomas -
• Cancer of lymphatic tissues-lymphocyes, lymph nodes, lymph
vessels and lymphoid organs
• Accounts for 5% of total human cancers
•Two Types-
1. Hodgkin’s Lymphoma – Large, Binuclated cells called Reed-
Sternberg cells
2. Non Hodgkin’s Lymphoma – Do not contain Reed-
Sternberg cells
14.
15. •Increased production of lytic
enzymes
•Genetic alterations
•Induction of neoplasm in
experimental animals
•Altered signal transduction
mechanism
•Alterations in electric charge
•Ability to host’s anti-tumor
immune response
•Alteration in cell membrane
structure and functions
Characteristics of Cancer Cells
•Infinite growth (Immortality)
•Metastasis
•Invasiveness
•Loss of contact inhibition
•Loss of anchorage
dependence
•Reduced serum requirements
•Growth factor independence
•Loss of cell differentiation
•Inhibition of apoptosis
•Angiogenesis
•Changes in cytoskeleton
•Changes in cell morphology
and cytology
16. HYPOTHESIS ABOUT CANCER
1. Somatic Mutation Hypothesis
i. Mutational activation of repressed genes
ii. Mutational blocking of repressed proteins that keep gene in
repressed condition
iii. Chromosomal abnormalities and cancer go hand in hand
2. Defective Immunity Hypothesis
• Insufficient number of lymphocytes-mutation, stress, poor
nutrition
• Immunological surveillance
3. Viral Gene Hypothesis
Viruses are responsible for the Cancer
17. 3. Viral Gene Hypothesis -
Evidences –
1. Demonstration of transmission of leukemia by cell free
filtrates of blood from diseased chicken to healthy
chicken
2. Rous ( 1911) transmitted chicken sarcoma from diseased
chicken to healthy chickens
3. Viruses producing Cancer are called ‘Tumor / Oncogenic
Viruses,
4. Two types – DNA tumor & RNA tumor viruses
5. Common Property- Viral genome integrates into host
chromosomes
18. Five Groups-
Papova viruses
Adenoviruses
Pox viruses
Herpes viruses
Hepatitis viruses
Among these Papoviruses have received more attension
as they cause tumors in variety of animals
DNA Tumor Viruses
19. Name derived from first two letters of three viruses-
Papilloma virus
Polyoma virus
Simian vacuolating virus (SV 40)
They belong to papovaviridiae family
It includes two genera- Papiloma & Polyoma
SV40 are now included in Polyoma viruses
All of them are small , naked, icosahedral, circular,
double stranded DNA viruses about 55 nm in diameter
Papova viruses
20. Papilloma virus is associated with benign warts
Natural infection results in benign warts
Induce tumors only in natural hosts
Transform normal cells into cancer cell in vitro very rarely
Warts are usually benign , but may convert into malignant
carcinomas
Also associated with penile, uterine & cervical cancer
Replicate exclusively in Keratinocytes(Outermost layer
of skin
Polyoma virus – Polyoma means multiple tumors
Do not induce tumors in natural hosts like monkey & mouse
For example- SV 40 do not induce tumor in monkeys
but induce sarcoma in hamster
SV 40 is most thoroughly studied oncogenic DNA virus
Other examples are JC & BK virus
21.
22. Termed as ‘Oncorna viruses’
Family- Retroviridiae – Retroviruses – icosahedral , enveloped,
two segments of RNA, reverse transcriptase
Five Categories- Based on host range & disease type
Avian leukosis complex – Rous sarcoma virus of
chickens
Murine leukosis virus- Murine lukemia & sarcoma
viruses
Mammary tumor virus of Mice- Bittner virus
Leukosis sarcoma virus- Sarcoma in cats, hamster,
guinea pigs & monkeys
Huan T cell lymphotrophic Virus ( HTLV) – Type 1 & 2
Type 1 causes Adult T cell lymphoma
Type 2 causes hairy cell leukemia (Bone has difficulty in
producing normal WBCs, RBCs & Platelets
RNA Tumor Viruses
23. 1. Oncogene Theory
Proposed by Huebner & Todaro
Genetic information is present in each & every body cell
Transmitted from parents to offspring through germ cells
Infection has occurred millions of years ago during evolution
Thus, every cell is assumed to contain ‘oncogene’
It is normally kept in repressed condition
Derepression by physical, chemical & biological agents
2. Protovirus Theory
Proposed by Temin
DNA RNA DNA Reintegration into original DNA
Theories of Oncogenesis by RNA Tumor Viruses
25. 3. Provirus Theory
Proposed by Spiegelman
Direct infection with cancer viruses
Transmission is horizontal – from one individual to another
individual through provirus state
Among these oncogene hypothesis is cosistant with number of
observations