number 21 Done by Ahmad Rawajbeh Corrected by Omar Sami Doctor Maha Shomaf
Ability to Invade and Metastasize The metastatic cascade can be subdivided into two phases: 1-invasion of ECM and vascular dissemination: Metastasis starts by invasion through the surrounding tissues, which contain cells and matrix that the tumor cells react with. 2-homing of tumor cells: Reaching distant organs and survive, establishing blood supply and proliferating in the new site. Invasion of Extracellular Matrix (ECM) Human tissues are organized into a series of compartments separated from each other by two types of ECM: 1-basement membranes. 2-interstitial connective tissue. ECM is composed of: 1-collagens. 2-glycoproteins. 3-proteoglycans. -The normal cells can't move through tissues, but tumor cells have the ability to interact and destruct; so it is invasive and infiltrative. Invasion of the ECM is an active process that requires four steps: 1-Detachment of tumor cells from each other. 2-Degradation of ECM. 3-Attachment to novel ECM components. 4-Migration of tumor cells. - All these steps are accomplished by certain genes. - The wall of blood vessels is not permeable for cells, and there are no gaps to all of them to move through. >> Not all tumor cells are able to cross blood vessels and travel to a new organ, tumor cells that are metastatic only can do that.
Spends 3 minutes on this short video as a summary for metastasis>> https://www.youtube.com/watch?v=bdwrzd19swg
First step: Detachment (Loosening) of tumor cells from each other. -Here, we are mainly talking about carcinomas (epithelial malignant tumors). -Normal cells are connected together by attachments. However, these attachments are important, loss of them is a feature of malignancy. E-cadherin function is lost in almost all epithelial cancers by: 1-Mutational inactivation of E-cadherin genes. 2-By activation of β-catenin genes/since one of E-cadherin functions is to sequester beta-catenin. 3- By inappropriate expression of the SNAIL and TWIST transcription factors which suppress E-cadherin expression. Epithelial-to-mesenchymal transition (EMT): Loss of E-cadherin expression is the key event. The cells start transition after losing E-cadherin and start infiltration. EMT, and SNAIL and TWIST down-regulate E-cadherin expression. >> drugs that block these proteins can help as a therapy to prevent metastasis. EMT has been documented mainly in breast cancers. In EMT, carcinoma cells down-regulate certain epithelial markers (e.g., E-cadherin) and up-regulate certain mesenchymal markers (e.g., vimentin and smooth muscle actin). These molecular changes are accompanied by phenotypic alterations >> morphologic change from the polygonal epithelioid shape to a spindly mesenchymal shape.
Second Step: - Local degradation of the basement membrane and interstitial connective tissue. - The degradation of basement membrane is important. Differentiation between carcinoma in situ and infiltrative tumors by looking at the basement membrane under the microscope whether degraded or not. Tumor cells may either secrete proteolytic enzymes themselves or induce stromal cells (e.g. fibroblasts and inflammatory cells) to elaborate proteases. Multiple different families of proteases are present : 1-matrix metalloproteinases (MMPs). 2-cathepsin D. 3-urokinase plasminogen activator. MMPs also cause releasing ECM-sequestered growth factors thus enhancing tumor growth. Cleavage products of collagen and proteoglycans also have chemotactic, angiogenic, and growth-promoting effects. The collagenase is important. MMP-9 is a gelatinase that cleaves type IV collagen (collagen 4, the primary component of basement membranes.) Of the epithelial and vascular basement membrane and also stimulates release of VEGF from ECM. -Vascular Endothelial Growth Factor: new blood vessels formation. Benign tumors of the breast, colon, and stomach show little type IV collagenase activity. Malignant tumors overexpress this enzyme.
The levels of metalloproteinase inhibitors are reduced so that the balance is tilted greatly toward tissue degradation. Third Step: - Changes in attachment of tumor cells to ECM proteins. - Normal epithelial cells have receptors, such as integrins, for basement membrane laminin and collagens that are polarized at their basal surface. Help cells in movement after degradation of the basement membrane in a process similar to rolling that we see in inflammation. Loss of adhesion in normal cells leads to induction of apoptosis. The adhesion through these receptors help to maintain the cells in resting differentiated state >> loss of it means death, but this is with normal cells only. Cleavage of the basement membrane proteins, collagen IV and laminin by MMP-2 or MMP-9 generates novel sites that bind to receptors on tumor cells and stimulate migration. Final Step: - Locomotion. - Migration is a complex, multistep process that involve the actin in the cytoskeleton. - Changes in cytoskeleton allow the cell to move and migrate. Such movements seem to be potentiated and directed by tumor cellderived cytokines, such as Autocrine motility factors. *some growth factors (e.g. Insulin like growth factor 1and 2) and cleavage products of the matrix may have chemotactic activity.
* Stromal cells produce paracrine motility factors such as HGF/SF (hepatocellular growth factor/ scatter factor) that binds to receptors in tumor cells. The HGF/SF is detected with high levels in the highly invasive brain tumors (Glioblastomas), this supports their role in motility. Vascular Dissemination and Homing of Tumor Cells In the bloodstream, some tumor cells form emboli by aggregating and adhering to circulating leukocytes, particularly platelets. This aggregation gives them some protection from antitumor host effectors cells. most tumor cells circulate cells as single cells. Extravasation of free tumor cells or tumor emboli involves adhesion to the vascular endothelium. The site of Extravasation and the organ distribution of metastases generally can be predicted by the location of the primary tumor and its vascular or lymphatic drainage. Many tumors arrest in the first capillary bed they encounter (lung and liver most commonly). In many cases the natural pathways of drainage do not readily explain the distribution of metastases. e.g. lung cancers tend to involve the adrenals (this doesn't follow the venous and lymphatic drainage) with some regularity but almost never spread to skeletal muscle. The heart is very rare to develop metastasis because of something unique in its tissue does not allow metastatic cells to develop tumor. Same thing with skeletal muscles which are well vascularised; however, they are rarely the sites of metastases.
The mechanisms of site-specific homing involve: 1-The expression of adhesion molecules by tumor cells whose ligands are expressed preferentially on the endothelium of target organs. 2-Chemokines and their receptors. Chemokines participate in directed movement (chemotaxis) of tumor cells. Human breast cancer cells express high levels of the chemokine receptors CXCR4 and CCR7. The ligands for these receptors in the secondary sites: Important, if we block them we can prevent metastasis. (i.e chemokines CXCL12 and CCL21) are highly expressed only in those organs where breast cancer cells metastasize. After Extravasation, tumor cells are dependent on a receptive stroma for growth. The precise localization of metastases cannot be predicted with any form of cancer. - The tumor cells may reach an organ but this organ is not suitable so the tumor will not develop. The prolonged survival of micro-metastases without progression is well described in melanoma and in breast and prostate cancer. *********************************************************** Limitless Replicative Potential Most normal human cells have the capacity of 60 to 70 doublings(divisions). After this, the cells lose the capacity to divide and enter senescence. Why?
This phenomenon is due to progressive shortening of telomeres at the ends of chromosomes. Short telomeres are recognized by the DNA repair machinery leading to cell cycle arrest mediated by p53 and RB. Some of tumor cells having short telomeres can pass due to mutant p53 and RB genes. Cells in which the checkpoints are disabled by p53 or RB mutations the non-homologous end-joining pathway is activated as a last effort to save the cell joining the shortened ends of two chromosomes. The terminal ends of chromosomes join together to avoid death creating chromosomes with more than one center. The two ends are ligated without homologous template >> nonhomologous meaning. This video may help>> https://www.youtube.com/watch?v=-xcfgnxf_xg. This inappropriately activated repair system results in Di-Centric chromosomes that are pulled apart at anaphase resulting in new double-stranded DNA breaks. The resulting genomic instability from the repeated bridge-fusionbreakage cycles eventually produces mitotic catastrophe characterized by massive cell death. If during crisis a cell manages to reactivate telomerase, the bridgefusion-breakage cycles cease and the cell is able to avoid death. During this period of genomic instability that precedes telomerase activation, numerous mutations could accumulate. Passage through a period of genomic instability probably explains the complex karyotypes frequently seen in human carcinomas. The Karyotyping, which is a term describing chromosomes number, size and appearance, determines the outcomes and prognosis of the tumor.
Telomerase, active in normal stem cells, is normally absent from, or at very low levels in most somatic cells. Telomere maintenance is seen in virtually all types of cancers. In 85-95% of cancers, this is due to up-regulation of the enzyme telomerase. Unregulated proliferation in incipient tumors leads to telomere shortening, followed by chromosomal instability and mutation accumulation; Reactivation of telomerase in these cells causes extension of telomeres and mutations become fixed contributing to tumor growth.
Grading of Cancer The grading of a cancer attempts to establish some estimate of its aggressiveness or level of malignancy. It is based on: 1-the cytologic differentiation of tumor cells. By looking at them under the microscope and estimate the similarity with normal tissues. 2-the number of mitoses within the tumor. The cancer may be classified as grade I, II, III, or IV, in order of increasing anaplasia. >> the well differentiated one is classified as 1. Criteria for the individual grades vary with each form of neoplasia. Difficulties in establishing clear-cut criteria have led in some instances to descriptive characterizations as: Well-differentiated. Moderately-differentiated. Poorly-differentiated. Anaplastic tumors. Staging of cancer: - The extent of the spread of a tumor including the size, lymphatic spread, and venous spread.
Staging of cancers is based on: 1-The size of the primary lesion. 2-Its extent of spread to regional lymph nodes. 3-The presence or absence of metastases. -staging is very important in prognosis. This assessment is usually based on clinical and radiographic examination (CT scan & MRI) and in some cases surgical exploration. CT scan: (Computed tomography) special x ray series of images with different angles processed by computers to create cross sectional images. Two methods of staging are currently in use: 1-the TNM system (T, primary tumor; N, regional lymph node involvement; M, metastases) 2-the AJC (American Joint Committee) system.. -TNM is more used. In the TNM system, T1, T2, T3, and T4 describe the increasing size of the primary lesion: N0, N1, N2, and N3 indicate progressively advancing node involvement. M0 and M1 reflect the absence or presence of distant metastases. We collect all these components and determine the stage. In the AJC method, the cancers are divided into stages 0 to IV, incorporating the size of primary lesions and the presence of nodal spread and of distant metastases. Stage 0 the tumor is limited and in situ; The patient has good prognosis. Presence of metastasis decreases the significance of the size and means that the patient status is advanced with bad prognosis.
Staging has proved to be of greater clinical value than grading. #Percentages represent patient survive 5 years after the first diagnosis. TNM Staging of Colon Cancers Tumor T0 none evident Tis = in situ (limited to mucosa) T1 = invasion of lamina propria or submucosa T2 = invasion of muscularis propria T3 = invasion through muscularis propria into subserosa or nonperitonealized perimuscular tissue T4 = invasion of other organs or structures
Lymph Nodes (N) 0 = none evident 1 = 1 to 3 positive pericolic nodes 2 = 4 or more positive pericolic nodes 3 = any positive node along a named blood vessel Distant Metastases (M) 0 = none evident 1 = any distant metastasis 5-Year Survival Rates T1 = 97% T2 = 90% T3 = 78% T4 = 63% Any T; N1; M0 = 66% Any T; N2; M0 = 37% Any T; N3; M0 = data not available Any M1 = 4%
The doctor stopped here. From slides Laboratory Diagnosis of Cancer 1-Morphologic Methods : (H&E stain) A-excision or biopsy. B-fine-needle aspiration. C-cytologic smears (Papanicolaou). D-Frozen sections. Immunocytochemistry : Cytokeratin prostate-specific antigen (PSA) =prostate carcinoma. estrogen receptors =breast cancer. Flow cytometry is used routinely in the classification of leukemias and lymphomas. Fluorescent antibodies against cell surface molecules and differentiation antigens are used to obtain the phenotype of malignant cells. 2-Tumor Markers : A-PSA Prostatic carcinoma can be suspected when elevated levels of PSA are found in the blood. PSA levels are often elevated in cancer. PSA levels also may be elevated in benign prostatic hyperplasia PSA test suffers from both low sensitivity and low specificity. B-carcinoembryonic antigen (CEA). carcinomas of the colon, pancreas, stomach, and breast. C-α-fetoprotein. produced by : 1- hepatocellular carcinomas.
2-yolk sac remnants in the gonads. 3-teratocarcinomas. 4-embryonal cell carcinomas. 5-neural tube defect of the fetus. CEA and α-fetoprotein assays lack both specificity and sensitivity Pain Demands To Be Felt -The fault in our stars.