Cancer Cells

by : Rien Elfahri

This posting dedicated to people whoever have pain cause of cancer, expecially to my own sister in Sape Bima - that had been attacked by this terrible multi-hit.
Cancer cells appear differently than normal cells do under the microscope. Their nucleus is much larger than in normal cells, their chromosomes are irregular in distribution and the nucleoli in the nucleus are very prominent. When cancer cells are grown in culture in the lab they also appear different than normal cells. Rather than growing in neat single-layer sheets with one next to the other they grow more haphazardly. They have long processes that extend from the cells, they overlap one another and their shape is more rounded. Normal cells will continue to divide and grow in a culture plate until they touch a neighboring cell where they receive a signal to stop growing. Cancer cells, on the other hand, do not receive this signal and grow on top of each other forming piles of growing cells that resemble a tumor.
Normal cells require growth factors added to their growth medium to enable them to grow in culture. Cancer cells do not require the same amount of growth factors, possibly because they are able make their own growth factors. Normal human cells will grow for a short amount of time in culture and then die, while cancer cells tend to keep on growing. The term given for this ability is immortalization. Cancer cells in culture are immortalized or have unlimited growth potential.
Cancer cells also have a more immature appearance compared to normal cells. This is referred to as dedifferentiation, or they lack differentiation. As an embryo matures and develops, its cells differentiate. This means they take on more specific roles that are reflected in their appearance—kidney cells begin to look different than skin cells or breast cells. Cancer cells look less and less like the tissue they are part of and more like embryonic cells. They also produce embryonic proteins that are used as tumor markers such as carcinoembryonic antigen (CEA) and alpha fetoprotein (AFP).

Pathology
Tumors - are either malignant or benign depending upon their invasiveness. Benign tumors are less aggressive, less likely to invade the surrounding tissue, less likely to metastasize (spread) and are slower growing. Although it sounds as if they pose no threat to the individual, this is not always the case. A tumor in the brain especially can be life threatening and put pressure on the brain as it grows. A benign tumor may also secrete hormones that in high levels can be toxic to the individual.
A malignant tumor is more aggressive, more invasive into the surrounding tissue, faster growing and more likely to metastasize. Malignant tumors usually kill the individual if they are not removed. The diagnosis as to whether a tumor is benign or malignant is done on a small sample of the tumor, called a biopsy. A pathologist will microscopically examine a thin, stained slice of the tissue. The tumor is graded, or given a number from 1 -4 that corresponds to its degree of malignancy, with 4 being the most malignant and 1 being benign. The more malignant the tumor, the less organized the cells of the tissue are and the more anaplastic or dedifferentiated they appear.
The tumor is also staged which refers to the amount it has spread. This is done both by gross examination of the patient and by microscopic examination of the tissue. The staging relates to the patient's prognosis. The best prognosis is if the tumor is confined to the epithelial layer of an organ and not spread into the basement membrane. The prognosis is worse if the tumor cells have spread to adjacent lymph nodes. As a tumor grows, it becomes capable of both invasion and metastasis.
An organ of the body consists of epithelial cells that are supported by a basement membrane. (Epithelial cells are cells that form the tissue that covers internal and external surfaces of the body and is found on skin and mucosal surfaces.) The basement membranes separate the epithelial cells from connective tissues that are rich in blood vessels. As the tumor enlarges, it can grow into the surrounding tissue, through the basement membrane and into blood or lymph vessels. This is a critical point in the growth of a tumor. Now, a small piece of tumor can break off and travel through the circulation until it receives a signal to attach to the vessel wall. It can then move through the vessel, into the tissue bed, where it grows to become a secondary tumor. This is termed metastasis. Two common locations for metastasizing tumors are the lungs and the liver.
Cancer can also involve the immune system and individuals with weakened immune systems are often at increased risk for developing cancer. AIDS patients, for example, are at increased risk for developing some cancers, such as Kaposi's sarcoma. As a cell becomes cancerous, it develops different antigens on its cell surface that should be recognized by the immune system and removed. For some reason, the immune system does not remove tumors. Probably, many cancer cells do develop in the body that are identified and removed by the immune system. It is not understood why this happens occasionally but not consistently. There have been documented cases of spontaneous tumor regression which may be due to activation of the immune system.
These unique antigens expressed on the surface of cancer cells can be used to the patient's advantage in treating cancer. Monoclonal antibodies are proteins produced in the laboratory from a single clone of a B cell, the type of cells of the immune system that make antibodies. Antibodies, also known as immunoglobulins, are proteins that help identify foreign substances to the immune system, such as bacteria or a virus. Antibodies work by binding to the foreign substance to mark it as foreign. The substance that the antibody binds to is called an antigen. Monoclonal antibodies that can recognize and attach to the specific antigens found on cancer cells are now being used to target cancer cells directly.
Unfortunately, cancer may go undiagnosed until it is quite advanced. This is because the body has many ways to adapt itself to damage and so symptoms are reduced for some time. Metastasis may be present by the time cancer is diagnosed. Symptoms of cancer include pain emanating from the organ being stretched, as well as fever and weakness. As the disease progresses, cachexia (the wasting that occurs due to starvation and debilitation caused by the cancer) may occur. The patient becomes unable to mount an anti-inflammatory response and infections occur. These infections become the cause of death in most cancer patients.

Carcinogenesis
How does a cancer cell become a cancer cell? Most scientists agree that cancer is a "multi-hit" process—a process that requires a series of genetic mutations that occur either spontaneously, are inherited or are caused by specific carcinogens. There are several stages in the development of cancer: initiation, promotion and progression.
•Initiation. During initiation, a carcinogen interacts with and damages the DNA. Repair can occur after this point and the process can be reversed.
•Promotion. Promotion causes reproduction or proliferation of these damaged cells, forming a mass of cells or a benign adenoma. This stage is still reversible and removal of the promoting agent can stop the expansion of the tumor mass.
•Progression. Progression, however, is irreversible and involves a number of sequential mutations in genes including oncogenes and tumor suppressor genes. The end result of progression is a late adenoma that eventually converts to a malignant carcinoma.

References :

American Cancer Society, ed: Osteen, Robert T. Cancer Manual. Framingham, MA: The American Cancer Society, 1996.
McKinnell, Robert G, Ralph E. Parchment, Alan O. Perantoni, and G. Barry Pierce. The Biological Basis of Cancer. New York: Cambridge University Press, 1998.
Templeton, Dennis J., and Robert A. Weinberg. "Principles of Cancer Biology." In Clinical Oncology, edited by Gerald P. Murphy, Walter Lawrence, and Raymond E. Lenhard. Atlanta, GA: The American Cancer Society, 1995.
Weinberg Robert A. One Renegade Cell: How Cancer Begins. New York: Basic Books, 1998.
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