neoplasia 4

NEOPLASIA 4Fe A. Bartolome, MD, FPASMAP

Department of Pathology

Our Lady of Fatima University

Chemical Carcinogenesis


• Initiation results from exposure of cells to a sufficient dose of a carcinogenic agent (initiator).

• Initiation alone is not sufficient for tumor formation.

• Initiation causes permanent DNA damage (mutations). It is rapid and irreversible and has “memory.”


• Unrepaired alterations in the DNA are essential first steps in the process of initiation. For the change to be heritable,

the damaged DNA template must be replicated

For initiation to occur, altered cells must undergo at least one cycle of proliferation so that DNA change becomes fixed


• Promoters (e.g. Phorbol esters, hormones, phenols, and drugs) can induce tumors in initiated cells, but they are non-tumorigenic by themselves

• Tumors do not result when the promoting agent is applied before, rather than after, the initiating agent.

• The cellular changes resulting from application of promoters do not affect DNA directly and are reversible.


• Application of promoters leads to proliferation and clonal expansion of initiated (mutated) cells Mutated cells with reduced

growth factor requirements

• Process of tumor promotion includes multiple steps: proliferation of pre-neoplastic cells, malignant conversion, and tumor progression

Chemical Carcinogenesis: Initiators

Direct-Acting Agents

• Require no metabolic conversion to become carcinogenic

• Most are weak carcinogens; some are chemotherapeutic drugs (e.g. Alkylating drugs)

• Risk of induced cancer is low.


Indirect-Acting Agents

• Requires metabolic conversion to an ultimate carcinogen before they become active

• Polycyclic hydrocarbons present in fossil fuels; animal

fats during process of broiling meats; smoked meat and fish

Principal active product: epoxides form adducts with DNA, RNA, and proteins


Indirect-Acting Agents

• Most of the known carcinogens are metabolized by the cytochrome P-450-dependent mono-ozygenases

Example: benzo[a]pyrene light smokers with the susceptible genotype CYP1A1 with 7x higher risk of developing lung cancer


Molecular Targets

• DNA is the primary target

• Any gene may be the target commonly mutated are RAS and p53

Aflatoxin B1 cause G:C T:A transversion in codon 249 of p53

Radiation Carcinogenesis

Ultraviolet Rays

• UV rays derived from sun increased incidence of SCCA, basal cell carcinoma, and skin melanoma

• Degree of risk depends on:1. Type of UV ray2. Intensity of exposure3. Quantity of light-absorbing

protective coat of melanin

UVB radiation is the main cause of sunburn and skin cancer although mounting evidence suggests UVA may also play a role. UVB does not penetrate the skin as deeply as UVA but has more energy and therefore does more damage to the skin.

UVB sunlight is directly absorbed by DNA resulting in single strand breaks and the formation of pyrimidine

dimers.


Ionizing Radiation

• Electromagnetic (x-rays, gamma rays) and particulate (α particles, β particles, protons, neutrons) radiation are all carcinogenic

• Lead to formation of reactive oxygen species or free radicals


Ionizing Radiation

• High vulnerability: acute and chronic myeloid leukemia; thyroid cancer (only in the young)

• Intermediate: breast, lungs, salivary glands

• Resistant: skin, bone, GIT

DNA is damaged due to ionization or excitation caused by radiation. Clustered DNA damage would be produced where the density of ionization/excitation is high, whereas the isolated damage would be generated where it is low.

Microbial Carcinogenesis


Oncogenic RNA Viruses: HTLV type 1

• Only human retrovirus firmly implicated in causation of cancer in humans (T-cell leukemia/lymphoma)

• Does not contain an oncogene

• Viral integration shows clonal pattern site of integration identical within all cells of a given cancer



• With tax regulatory gene1. stimulates viral mRNA transcription 2. activate transcription of several

host cell genes involved in proliferation and differentiation of T cells FOS gene – immediate early gene Genes encoding IL-2 & its

receptor Gene for myeloid growth factor

granulocyte-macrophage colony-stimulating factor



• With tax regulatory gene3. Inactivates the cell cycle inhibitor

p16/INK4a and enhance cyclin D activation

4. Activate NFκβ activation of anti-apoptotic genes

5. Interfere with DNA repair functions6. Inhibits ATM-mediated cell cycle

checkpoints activated by DNA damage


Oncogenic DNAViruses: HPV

• High-risk HPVs: types 16 and 18 squamous cell CA of cervix and anogenital region; penile cancer; oropharyngeal CA

• HPV genome integrated into host genome site of integration random but pattern of integration is clonal

Naturally occurring cancers associated with papillomaviruses [10, 13].

Species Cancer Predominant viral types

Humans Skin carcinomas HPV-5, -8

Lower genital tract cancers HPV-16, -18, -31, -33

Malignant progression of respiratory papillomas

HPV-6, -11

Cattle Alimentary-tract carcinoma HPV-4

Eye and skin carcinoma Not characterized

Sheep Skin carcinoma Not characterized

Cottontail rabbit Skin carcinomaCotton rabbit papillomavirus (CRPV)

Shehata Cancer Cell International 2005 5:10 doi:10.1186/1475-2867-5-10


Oncogenic DNAViruses: HPV

• Viral genome integration interruption of viral DNA within E1/E2 open reading frame loss of E2 viral repressor and overexpression of oncoproteins E6 and E7


Oncogenic DNAViruses: EBV

• Associated with African form of Burkitt’s lymphoma, a subset of Hodgkin lymphoma, nasopharyngeal Ca and some gastric carcinoma

• Infects B cells and possibly epithelial cells of the oropharynx via complement receptor CD21



• Infection of B cells is latent no viral replication and destruction of cells

• Involves the “hijacking” of several normal signalling pathways



• EBV gene LMP-1 (latent membrane protein-1):1. acts as oncogene behaves like a

constitutively active CD40 receptor stimulate B cell growth

2. Activate NFκβ and JAK/STAT signalling pathways

3. Promote B cell survival and proliferation

4. Activate BCL2 – prevent apoptosis5. Induce expression of pro-

angiogenic factors (VEGF, FGF-2, MMP9, COX2)



• EBV gene EBNA-2 1. Encodes a nuclear protein that

mimics a constitutively active Notch receptor

2. Transactivates several host genes cyclin D and src family of proto-oncogenes



• EBV genome contains a viral cytokine vIL-10 hijacked from the host genome prevent macrophages and monocytes from activating T cells

• Impair immune competence allow sustained B-cell proliferation

• Cause translocations that activate c-MYC oncogene


Oncogenic DNAViruses: HBV and HCV

• Genomes do not encode any viral oncoproteins

• No consistent pattern of integration in liver cells

• Immunologically-mediated chronic inflammation with hepatocyte death regeneration and genomic damage


Helicobacter pylori

• First bacterium classified as a carcinogen

• Implicated in gastric adenocarcinoma and gastric lymphomas

• Involves increased epithelial cell proliferation in a background of chronic inflammation contain genotoxic agents such as ROS


Helicobacter pylori

• Contains a “pathogenicity island” that contains cytotoxin-associated A (CagA) gene Penetrates into gastric epithelial

cells initiate signalling cascade that mimics unregulated growth factor stimulation

• Additional mutations may be acquired (e.g. (11:18) translocation) cause constitutive activation of NF-κβ

Tumor Immunity

Immune surveillance

• A normal function of the immune system is to survey the body for emerging malignant cells and destroy them (+) lymphocytic infiltrates around

tumors and in LN draining sites of cancer

Increased incidence of cancer in immunocompromised individuals

Demonstration of tumor-specific T cells and antibodies

Tumor Immunity

Tumor antigens

• Poorly immunogenic• Initially classified as:

1. Tumor-specific antigens Present only on tumor cells and

not on any normal cells

2. Tumor-associated antigens Present on tumor cells and also

on some normal cells

Tumor Immunity

Tumor antigens

• Modern classification based on molecular structure and source

1. Products of mutated genes Synthesized in cytoplasm of

tumor cells enter class I or class II MHC pathways

Not present in normal cells do not induce self-tolerance

Tumor Immunity

Tumor antigens

2. Overexpressed or aberrantly expressed cellular proteins May be normal cellular proteins

abnormally expressed in tumor cells elicit immune response

Tumor Immunity

Tumor antigens

3. Antigens produced by oncogenic viruses Most potent: proteins produced

by latent DNA viruses (e.g. HPV and EBV)

Tumor Immunity

Tumor antigens

4. Oncofetal antigens (CEA, AFP) Proteins that are expressed at

high levels on cancer cells and in normal developing (fetal) but not adult tissues

Genes silenced during development and activated during malignant transformation

Tumor Immunity

Tumor antigens

5. Altered cell surface glycolipids and glycoproteins Include gangliosodes, blood group

antigens, and mucins present at higher levels in cancer cells than on normal cells

Melanomas: high levels of gangliosides GM2, GD2, and GD3

Target for cancer therapy with specific antibodies

Loss of normal topology and polarization of epithelial cells in cancer results in secretion of mucins into the bloodstream. The tumor cells invading the tissues and bloodstream also present such mucins on their cell surfaces

Cancer cells entering the bloodstream form complex thromboemboli with platelets and leukocytes, which are thought to facilitate arrest at ectopic sites, assist interactions with the endothelium, and help in evasion of the immune system. Current data suggest that this phenomenon can be explained by interactions between platelet and/or endothelial P-selectin and carcinoma mucins.

Tumor Immunity

Tumor antigens

6. Cell type-specific differentiation antigens Specific for particular lineages or

differentiation stages of various cell types

Typically normal self-antigens do not induce immune response

Potential targets for immunotherapy and for identifying the tissue of origin of tumors

Tumor Immunity

Anti-tumor Effector Mechanisms

1. Cytotoxic T lymphocytes

Play a protective role against virus-associated neoplasms

Demonstrated in blood and tumor infiltrates of cancer patients

In this diagram the various mechanisms elicited by stress for stimulating innate and adaptive immunity against cancer are illustrated.

Tumor Immunity


2. Natural killer cells

Capable of destroying tumor cells without prior sensitization may form first line of defense vs. Tumor

Activated by IL-2 and IL-5; may be activated by tumors that fail to express MHC class I antigens

NKG2D proteins activating receptors; recognize stress-induced antigens expressed on tumor cells

Tumor Immunity


3. Macrophages

Activated by interferon-gamma secreted by T cells and NK cells

Kill tumors by mechanisms similar to those used to kill microbes or by secretion of TNF

Tumor Immunity


4. Antibodies

No evidence of protective effects of antitumor antibodies against spontaneous tumors

Monoclonal antibody vs. CD20 (B-cell surface antigen) treatment of lymphomas

Tumor Immunity

Tumor Evasion of Immune System

1. Selective outgrowth of antigen-negative variants

Elimination of strongly immunogenic subclones during tumor progression

Tumor Immunity


2. Loss or reduced expression of MHC molecules

Failure to express normal levels of class I MHC molecules escape CTLs but may trigger NK cells

Tumor Immunity


3. Lack of co-stimulation

Express peptide antigens with class I molecules but without co-stimulatory molecules prevent sensitization and render T cells anergic or undergo apoptosis

Express arginase arginine essential component of TCR loss of T cell recognition

Tumor Immunity


4. Immunosuppression

TGF-β secreted in large quantities by many tumors potent immuno-suppressant

Immune response induced by the tumor may inhibit tumor immunity by activation of T-cell inhibitory receptor CTLA4

Tumor Immunity


4. Immunosuppression

Production of COX2 decreased IL-10 and increased IL-12 immunosuppression and promotion of metastasis

Tumor Immunity


5. Antigen masking

Cell surface antigens of tumors may be hidden, or masked, by glycocalyx molecules expressed in greater amounts in tumor cells

Tumor Immunity


6. Apoptosis of CTLs

Some melanomas and hepatomas express FasL kill Fas-expressing T lymphocytes that come in contact with them

Tumor Immunity


7. Dendritic cell defects

a) Tumor secretion of growth factors inhibit formation of DCs in bone marrow

b) Increased IL-10 levels decreased expression of CD80 and CD86 decreased T cell activation

c) Tumor secretion of nitric oxide and hydrogen peroxide DCs undergo cell death

Clinical Aspects of Neoplasia

• Both malignant and benign tumors cause problems because of:1. Location and impingement on

adjacent structures2. Functional activity (e.g. Hormone

synthesis or development of para-neoplastic syndrome)

3. Bleeding and infections due to ulceration of tumor through adjacent surfaces

4. Symptoms due to rupture or infarction

5. Cachexia or wasting


Local and Hormonal Effects

• Cancers arising within or metastatic to an endocrine gland endocrine insufficiency

• Hormone production seen in neoplasms arising in endocrine glands more typical of benign tumor

• Neoplasms in the gut obstruction or intussusception


Local and Hormonal Effects

• Non-endocrine tumors may elaborate hormones or hormone-like products paraneoplastic syndromes

• Melena and hematuria characteristic of neoplasms of the gut and urinary tract


Paraneoplastic Syndromes

• Symptom complexes in cancer-bearing individuals that cannot readily be explained, either by the local or distant spread of the tumor or by the elaboration of hormones indigenous to the tissue from which the tumor arose



• Significance:1. May present the earliest

manifestation of an occult neoplasm2. May represent significant clinical

problems in the affected patients3. May mimic metastatic disease

which may complicate treatment



1. Endocrinopathies

Ectopic hormone production Cushing syndrome – most

common endocrinopathy 50% with small cell CA of lungs; due to excessive corticotropin production



2. Hypercalcemia

Most common paraneoplastic synd.

Two processes involved:1. Osteolysis induced by cancer2. Production of calcemic

humoral substances in extra-osseous neoplasms



3. Acanthosis nigricans

Gray-black patches of verrucous hyperkeratosis on the skin

Genetically determined; juveniles or adults


Cancer Cachexia

• Progressive loss of body fat and lean body mass accompanied by profound weakness, anorexia, and anemia

• Weight loss results equally from loss of fat and lean muscle

• Due to increased basal metabolic rate despite reduced food intake

LMF – lipid-mobilizing factor induce breakdown of adipose into fatty acids; PIF – proteolysis-inducing factor induce protein degradation in skeletal muscles. Tumours convert glucose to lactate, which is transferred to the liver, where it is converted back into glucose. This cycle uses a large amount of energy, and might contribute to cachexia.

Grading and Staging

Cancer Grading

• Based on degree of differentiation of the tumor cells and, in some cancers, the number of mitoses or architectural features

• Provides information about potential behavior of tumor

• Of less clinical value than staging

Grading and Staging

Cancer Staging

• Based on:1. Size of primary lesion2. Extent of spread to regional LN3. Presence or absence of blood-

borne metastases

• Gives an idea of how extensive or widespread the cancer is

• Determines treatment and outlook for recovery

Laboratory Diagnosis

Histologic and Cytologic Methods

• Sampling approaches:

1. Excision or biopsy Quick-frozen section desirable

determine the nature of a mass lesion or in evaluating the margins of an excised cancer




2. Fine-needle aspiration Aspirating cells and attendant

fluid with a small-bore needle Used for more readily

palpable lesions in breast, thyroid, and LN

Less invasive and more rapidly performed




3. Cytologic (Papanicolau) smears Screen for cervical carcinoma

and also endometrial CA, bron-chogenic CA, bladder and prostatic tumors, and gastric CA

For ID of tumor cells in abdominal, pleural, joint, and cerebrospinal fluids


Immunohistochemistry

• Uses:

1. Categorization of undifferentiated malignant tumors

(+) cytokeratins carcinoma (+) desmin muscle cell

origin



• Uses:

2. Determination of site of origin of metastatic tumors

Detect tissue-specific or organ-specific antigens in a biopsy specimen of the metastatic deposit (e.g. PSA)



• Uses:

3. Detection of molecules that have prognostic or therapeutic significance

e.g. Detection of hormone receptors in breast cancer cells of prognostic and therapeutic value


Flow Cytometry

• Rapidly and quantitatively measure individual cell characteristics (e.g. Membrane antigens, DNA content of tumor cells)

• Useful in ID and classification of tumor arising from T and B cells, and from mononuclear-phagocytic cells


Molecular Techniques

1. Diagnosis of malignant neoplasms

2. Prognosis of malignant neoplasms

3. Detection of minimal residual disease

4. Diagnosis of hereditary predisposition to cancer

Tumor Markers

• Biochemical assays for tumor-associated enzymes, hormones, and other tumor markers in the blood

• Contribute to detection of cancer

• Useful in determining the effectiveness of therapy or appearance of recurrence

neoplasia 4

Technology