 Cells that continue to replicate, fail to differentiate into specialized cells, and become immortal are called tumor.  Cancer is a group of diseases characterized by unregulated cell growth and invasion and spread of cells from the site of origin to other sites of the body muscle, nerve, bone, blood

 The aberrant growth pattern results from mutation of genes that regulate proliferation, differentiation and survival of cells in a multi cellular organ.

Terminologies  Oncogenes: encode proteins that associated with oncgenesis  Transformation: stable and heritble change in the genes for growth control  Contact inhibition: Stop growing upon contact with neighboring cell  Immortalization: Cell divides for indefinite period  Benign tumor: Composed of cells with abnormal growth but non-invasive  Malignant tumor: Composed of cells with abnormal growth that invade to other organs  Metastasis: Invasion of cancer to other part of the body  Neoplasm: formation of new cells  Hyper plastic: abnormal cell growth

Altered morphology Loss of contact inhibition (ability to grow over one another) Ability to grow without attachment to solid substrate (anchorage independence) Ability to proliferate indefinitely (immortalization) Reduced requirement for mitogenic growth factors High saturation density (ability to accumulate large numbers of cells in culture dish) Inability to halt proliferation in response to deprivation of growth factors

Oncogenes: Mutated derivatives of normal genes proto oncogenes-functions of protooncogenes are 1. promote proliferation and cell survival 2. Codes for Growth factors, Growth factor receptors, Signal transduction proteins, Intracellular kinases and Transcription factors.  Mutation in only one copy of proto oncogenes initiate transformation of cell to malignant form

Tumor Suppressor genes  Normal growth suppressor genes  Codes for proteins that 1. Inhibit cell growth and proliferation 2. Promote cell death 3. Repair DNA  Both alleles of tumor suppressor genes need to be inactivated for any transformation

 A stimulatory pathway will become hyperactive if a mutation causes any component such as a growth factor receptor to issue stimulatory messages autonomously without waiting for commands from upstream  An inhibitory pathway will shut down when some constituent such as a cytoplasmic relay is eliminated and thus breaks the signal chain

 Normal cell growth depends on balanced regulation of cell cycle and apoptosis by protooncogenes and tumor suppressor genes.  Cell cycle check point : product of tumor suppressor genes slow the growth in response of signal in cell cycle check point  Cells with irreversible damage undergoes apoptosis initiated either by death ligands or intrinsic signals

 The molecular switch always keep in ON position leads to excessive cell proliferation by the following two ways 1. Over activity of stimulatory proteins- In case of breast cancer cells produce excess cyclin D and E 2. Inactivation of inhibitory proteins- half of all cancers initiated with lack of functional p53 protein

 Inactivation of p53 in tumors reduces the likelihood that genetically troubled cells will be eliminated  Cancer cells may also make anti apoptopic bcl2 proteins which ward off apoptosis efficiently

Hyperplasia  Cells in a tissue overgrow  Resulting defined mass: tumor (neoplasm)  Benign, e.g., moles  Slow growth  Expands in the same tissue; does not spread  Cells look nearly normal  Malignant  Rapid growth  Invades surrounding tissue and metastasizes  Cell differentiation usually poor

Dysplasia  Abnormal change in the size, shape, and organization of cells in a tissue  Often an early step toward cancer  Microscopic characteristics of cancer cells  Behave differently from normal cells  It is important to note that not all cancers form solid tumors. For example, leukemia is a cancer of the blood where individual cells circulate within the bloodstream.

 Carcinoma: arising from epithelial tissue, such as glands, breast, skin, and linings of the urogenital, digestive, and respiratory systems (89.3% of all cancers)  Sarcoma: cancer that originates in muscle, fibrous tissue, fat, bone, cartilage or other connective or supportive tissue.  Leukemia: cancer that originates in blood forming tissue such as the bone marrow or spleen. Large numbers of abnormal cells are produced which enter and circulate in the bloodstream.  Lymphoma: cancer that originates in cells of the lymphatic system, which is a network of vessels and nodes that acts as the body’s filter.  Central nervous system: cancer that originates in the tissues of the brain and spinal cord.

Benign vs. Malignant Tumors BenignMalignant Grow slowlyGrow rapidly Well-defined capsuleNot encapsulated Not invasiveInvasive Well differentiatedPoorly differentiated Low mitotic indexHigh mitotic index Do not metastasizeCan spread distantly (metastasis)

Most cancer cells have increased number of mutations then the normal cells. Two major types of change in genome 1.Somatic mutation As the cancer progresses, the number of mutation increases Inactivation of mutator genes decreases the repair damage of DNA, and increase the rate of mutation

2. Genetic instability Reflected the changes of number of genes in cancer cells result from  Duplication or deletion  Translocation  Changes affect entire chromosome

When cells are placed in culture, -grow for division -enter a senescent stage -go through the crisis - survival of crisis are capable of dividing indefinitely initiate tumor Three types of changes that occur when a cell becomes tumorigenic -Immortalization -Transformation -Metastasis

 The counting system in molecular device that counts the number of doublings through which a cell population has passed and at appropriate times initiate senescent and crisis  Telomere are DNA segments present at the ends of chromosome  The telomere caps protect the chromosomal ends from damaging

 Telomere shorten a bit every time chromosome replication during S phase  Once telomere shrink below the threshold level they gives an alarm that instruct the cell to enter senescent stage  If cells bypass senescent stage further shrinkage of telomere will eventually trigger crisis  Extreme shortening of telomeres will cause chromosome fuse with one another or to break apart creating genetic caos that is fetal

 Telomerases systematically replaces telomeric segment that are usually trimmed away during cell cycle  Over activation of gene that codes for the enzyme telomerases during the development of most cancer cell  Maintaining integrity of telomeres enables the cell to replicate endlessly that allows- 1. Tumor cell to grow large 2. Give time to accumulate for mutation in cells 3. Increase the ability of cells proliferation and ultimately metastasize

1. Genetic factors: mutations, translocation, amplifications 2. Environmental factors: UV, chemicals, viral infections  conversion of proto-oncogenes (potential for cell transformation) to oncogenes (cell transformation)  alteration in tumor suppressor genes

 Cancers can result from expression of mutant from proteins like: - Growth factors (I) - Growth factor receptors (II) - Signal transduction Proteins (III) - Transcription factors (IV) - Pro- or anti- apoptotic proteins (V) - Cell cycle control proteins (VI) - DNA repair proteins (VII)

. Growth factor (I) Growth factor receptor (II) Intracellular transducer (III) Intracellular effector region (PTK) Second messenger (phosphorylated proteins) Transcription factors (IV) DNA Transcription DNA repair Proteins (VII) RNA Cell cycle control proteins (VI) mRNA Protei ns Anti-apoptosis proteins (V) Intracellular receptors (II) Virus encoded activators of growth –factor receptors (Ia)

 Mechanisms of activation of proto oncogene and converting to a cancer gene vary - over expression - constituently active - express in wrong time - express in wrong place Interaction of proto-oncogene product with other proteins altered

 Transduction by retroviruses  Insertional mutagenesis  Translocation  Gene amplification  mutation

 Cellular proto oncogenes may transduced into retroviral genome  Transduced gene replicated and transmitted like viral genes  Upon infection the transduced gene expressed abundantly under viral signal

 Insertion of a retroviral promoter adjacent to cellular oncogene  First occurred in avian leucosis virus Host gene 5’LTR 3’ LTR C - myc

 Translocation of a proto-oncogene near a strong regulatory sequence  Translocation may affect the expression of proto- oncogene or gene product Translocation in Burkitt’s lymphoma H pro. H-gene C-myc pro. C-myc gene H pro. C-myc gene C-myc pro. H-gene Chromosome 14 8

 Increase in copy number of a potential gene resulting in excess production of the encoded protein  Amplification of oncogene HER-2/neu occur in breast cancer  Gene amplification mostly occur at the late stage of tumor progression

 Point mutation or deletion might change the function of a protein,  Substrate specificity,  cell binding property,  Binding specificity of a transcription factors etc.  Altered protein may lead to oncogenic activation, eg. C-ras gene

Oncogenic Viruses  DNA Viruses - Human papilomaviruses (HPV) - Epstein Barr Virus (EBV) - Hepatitis B Virus (HBV)  RNA Viruses -Retroviruses -Hepatitis C Virus  RNA tumor viruses introduce a transforming gene into the cell (HCV)  DNA tumor viruses induce or alter the expression of a pre existing cellular gene/s (proto-oncogene)

Non-specific: NK cells,  T cells macrophages Antigen-specific: Antibody (ADCC, opsinization); T cells (cytokines, Fas- L, perforin/granzyme)

NK/T Tumor NK/ T cells IFN-  Perforin/granzyme B Fas-L/Fas apoptosis

sIg Tumor Complement Macrophage/ opsinization FcR FabFc NK cells & ADCC Tumor

MHCI peptide Apoptosis T cell receptor (TCR) CD8 Tumor IFN-  Granzyme B

 The c-ras proto-oncogene can transformed to oncogene by single base mutation.  The mutations at position 12 or 61, found in several human tumors.  The ras genes appear to be finely balanced at the edge of oncogenesis. Almost any mutation at either position 12 or 61 can convert a c-ras proto-oncogene into an active oncogene. -All three c-ras genes have glycine at position 12. If it is replaced in vitro by any other of the 19 amino acids except proline, the mutated c-ras gene can transform cultured cells. -Position 61 is occupied by glutamine in wild-type c-ras genes. Its change to another amino acid usually creates a gene with transforming potential.

 Some mutant c-ras genes that have changes in the protein sequence also have mutation that increases the level of expression by 10x.  When the expression of a normal c-ras gene is increased, either by placing it under control of a more active promoter or by introducing multiple copies into transfected cells, recipient cells are transformed. Oncogenesis depends on over-activity of Ras protein, and is caused either by increasing the amount of protein or (more efficiently) by mutations that increase the activity of the protein.

- Ras is active when bound to GTP and inactive when bound to GDP. It has an intrinsic GTPase activity. The activation of Ras is controlled by GTP. -GAP stimulate the ability of Ras to hydrolyze GTP, thus converting active Ras into inactive Ras. - GEF stimulate the replacement of GDP by GTP, thus reactivating the protein

 Constitutive activation of Ras caused by mutations allow the GDP-bound form of Ras to be active or prevent hydrolysis of GTP.  Many mutations that confer transforming activity inhibit the GTPase activity. Inability to hydrolyze GTP causes Ras to remain in a permanently activated form  Its continued action upon its target protein is responsible for its oncogenic activity.