One approach to understanding the senescent growth arrest is to examine the factors that are required for the division of young cells and to determine whether the senescent cells are able to respond to these factors. Any defect in their response would presumably shed light on the mechanism of the growth arrest. In virtually all cell types, cell division is regulated by the presence of growth factors. Growth factors are small proteins that bind to specific receptors on the surface of cells. The receptors for growth factors contain intrinsic enzymatic activity that is activated by growth factor binding. (more…)

Although many possible explanations for the mechanism that underlies the Hayflick limit have been proposed, it is still not clear what triggers the irreversible growth arrest seen in cellular senescent. A loss of telomeres, DNA at the end of each chromosome, has been considered an attractive candidate for the senescent trigger. The hypothesis was that a small amount of the telomere at the end of the chromosome (which is linear) is lost at each cell division due to the directionality of DNA polymerase. DNA polymerase can completely replicate one strand of DNA but cannot begin at the very end of the opposite strand. (more…)

Animal studies support a cancer-promoting role for fat, and in humans, epidemiological data strongly suggest that dietary fat intake may be associated with incidence and mortality of cancers of the breast, colon, rectum, and prostate. There are also data implicating fat in cancers of the ovaries, uterus, pancreas, and lung, but the evidence is not as strong. There is still a debate as to whether it is total dietary fat, specific fats, or total calories that are involved in carcinogenesis. In any event, cancers of breast, colon, and prostate are highest in North America and western Europe and lowest in Asia, and are directly related to the intake of total fat in the diet even when adjusted for total calories. (more…)

Growth factors are proteins that regulate the cell; they function by binding to specific receptor molecules in the cell membranes and thereby stimulating receptor-mediated activation of intracellular signal transduction pathways. These pathways are activated beginning with stimulation of tyrosine kinase to phosphorylate other proteins. These are both stimulatory and inhibitory growth factors. (more…)

In every population of cells there are three types of cell. The first group consists of cycling cells, which continuously proliferate by going from one mitosis to the next. The second is composed of terminally divided cells, which will die without ever dividing again. In the third group the cells are not dividing, but can re-enter the cell cycle if the appropriate stimulus is supplied. This phase is termed G0. (more…)

Much of cell death is genetically programmed by the process called apoptosis. In apoptosis, when the cell is damaged, the DNA initiates cell destruction, or suicide, and the cell is slowly broken into small packages that are removed by phagocytic cells, and there is no inflammation. In cancer, not only does proliferation occur, but apoptosis is blocked, resulting in accumulation of abnormal cells.

Scientists are beginning to investigate mechanisms of restoring and inducing apoptosis in cancer cells. Several approaches are being sought; one is to introduce apoptosis signals, allowing the cancer cells to die while rescuing the normal cells. Another is to reintroduce into the cancer a normal gene involved in setting off apoptosis, such as the normal p53 gene; a third method is to shut off proliferation genes (such as mutated Ras), which by itself inhibits apoptosis. If the mutated Ras gene is shut down, apoptosis will start up again and cancer cells will die.

Cancer kills people because the tumor both invades and metastasizes. Approximately 30% of patients newly diagnosed with a cancer have detectable metastatic disease. About another 30% have occult metastases (micrometastases) that will become evident in time. Thus, 60% of cancer patients will have multiple dormant metastases and will ultimately fail therapy and die of the cancer. The formation of metastases begins early in the growth of the primary tumor and increases with time. Small metastases up to 1 mm in size receive nutrition by diffusion but need to have new blood vessels (neo-vascularization) to grow larger. There has been a long search for the angiogenic ‘switch.’ Some target molecules and new therapies are being developed to thwart this neovascularization.

Cancer traditionally was classified as being either a carcinoma or a sarcoma named for the presumed cell of origin: epithelial (carcinoma) or mesenchymal (sarcoma). Recent evidence has demonstrated that most if not all neoplasms arise from immature stem cells that then differentiate along normal cell lines, but mutate and acquire the properties of autonomous growth as described previously. We now realize that carcinomas of the lung, breast, and stomach do not arise from well-differentiated ‘normal’ cells in these organs but from stem cells that begin to differentiate in the di- rection of these tissues but then become autonomous and have impaired apoptosis. These cells lose their normal self-limiting capacity and acquire properties that allow them to enter the circulation and spread to other organs. These cancer cells are the ‘seed,’ and if other organ’s ‘soil’ supports their growth, metastases grow distant to the primary site. Cancers of the lymphatic system or blood-forming cells are termed hematopoietic malignancies. Lymphoma, leukemia, and multiple myeloma are the most common of the hematopoietic malignancies. Thus, a neoplasm is usually named by what the cells resemble and where they arise. A cancer of the lung implies that the cells resemble lung cells and arise in that organ. An osteosarcoma resembles bone cells and is found in bone. Leukemia resembles white cells and is found in the bone marrow. It is still useful to classify cancer cells as a carcinoma, a sarcoma, or hematopoietic, as there are specific tumor markers (proteins on the cell surface) that are present on the tumor cells and that can be detected by the pathologist using different immunohistochemical staining techniques. The treatment depends on the cell of origin.

Cancers can have very different metastatic potential that depends upon their histologic type and intrinsic aggressiveness. It appears that metastasis occurs soon after the primary tumor vascularizes. Metastasis is a process separate from tumor formation. The genetic changes that lead to tumor formation do not by themselves cause erosion and metastases (see Table bellow). Invasion involves substances such as proteases, adhesion receptors, and motility cytokines. Metastases also involve these.

Progression of cancer and the positive and negative
influences on its growth and spread

Oncogenes are damaged versions of normal genes (‘proto-oncogenes’) that control cell growth and differentiation. It is important to realize that a proto-oncogene is a normal gene; it is only through pathological processes that it becomes an oncogene. Cancer is a multistep process in which multiple genetic alterations must occur, usually over many years. Thus, only after a long span of time will cell differentiation, division, and growth be changed. In human cancers, inherited mutations are relatively rare. (more…)

The sequencing of the human genome was begun in 1990 and completed in 2003. The International Human Genome Sequencing Consortium (2004) reduced the estimated number of human protein-coding genes from 35,000 to only 20,000–25,000. Each cell in the body contains the same genetic material, but only a few genes are expressed in each cell, which determines its phenotype. A gene consists of deoxyribonucleic acid (DNA). The gene will transcribe a ribonucleic acid (RNA). In the nucleolus the RNA transcribed is ribosomal RNA (rRNA), and in the nucleoplasm the RNA transcribed is messenger RNA (mRNA) and transfer RNA (tRNA). The DNA gene acts as a template to form RNA. (more…)

The classical view of carcinogenesis was that it was a two-‘hit’ process – initiation (genetic) and promotion (epigenetic). However, this is too simplistic for definition of carcinogenesis and it is now realized that there may be six or more independent genetic mutational events. The newer theory of carcinogenesis is that it is a multistage process driven by both genetic damage (initiation) and other cellular changes (promotion). Tumor initiation begins in cells through genetic mutations that may be caused by chemical carcinogens, viruses, and physical agents. (more…)

Cancer Genetic Markers Of Susceptibility is based after populations in the NCI Cohort Range in addition to collaborative case-control epidemiologic reports by using biospecimens. Through scanning that DNA collected from men and women participating in these kinds of reports, may get determined handed down genetic versions associated with cancer tumor possibility that may bring about fresh preventive, analysis, in addition to restorative interventions. (more…)