Demystifying The Biology Of Cancer
All over the world cancer brings about fear and many unanswered questions, not only in the medical community, but in patients and families who don’t understand what they are up against or perhaps why domestic cats can be immunized against Feline Leukemia yet researchers have failed to come up with a solid vaccine or a concrete cure for most types of cancer.
Only upon disconnecting from the emotions the term cancer exudes can one truly see cancer for what it is; an awesome yet deadly genetic blunder on the molecular level that continues to baffle the minds of the best oncology researchers in the world. A look into the basics of cancer can shed some light as to why it is so difficult to treat and cure.
What is Cancer?
Cancer is actually a group of diseases where cells grow out of control and eventually metastasize, or spread to other parts of the body. Cancer cells, also referred to as malignant cells, are cells whose DNA has been genetically altered thanks to a genetic predisposition to certain types of cancer such as breast cancer, unhealthy work environments like working around asbestos, poor choices such as smoking, aging, or seemingly for no good reason at all. (ONS 2006)
Cancer Statistics
The American Cancer Society (2007) estimates that 1,444,920 new cancer cases will be diagnosed in 2007, and roughly 559,650 Americans will die of cancer in the United States. In comparison the American Cancer Society estimated 76,890 more new cases and 4,050 fewer deaths when compared to the 2004 statistics.
80% of all types of cancer are diagnosed in people 55 years of age or older (American Cancer Society, 2000). Annual statistics are published each year by the American Cancer Society and can be found online at http://www.cancer.org/docroot/stt/stt_0.asp .
Cell Structure
A normal cell has a membrane, which surrounds and contains cytoplasm. Within the cytoplasm are various organelles that do the “work” of the cell. The mitochondrion provides energy, and the endoplasmic reticula (smooth and rough) are used to make proteins. (Itano & Taoka 2005) The Golgi apparatus is the storehouse of the cell. Near the center of the cell is the nucleus, which houses all of the genetic material and is responsible for cellular duplication. (Itano & Taoka 2005)
Nucleus of a Cell
The nucleus of the cell can be thought of as the government of the cell. All the directions for cell growth, division and blood vessel growth are made in the nucleus, and the message is sent to the organelles in the cytoplasm to bring about the work of the cell. (Itano & Taoka 2005) These messages are transcribed copies of genes that tell the cell what to do, such as to make insulin after you have eaten a meal.
Cell Division
The cells in the body usually divide when the body needs more cells. Imagine that when you wash your hands, you are washing off the outer cells on your hands. The body needs to replace these cells, so it tells certain cells to divide. However, the body is careful that it only tells the cells to divide when it needs more cells so that cell birth equals cell death.
We have cells that promote cell division, called proto-oncogenes, and we have cells that support them in check, called tumor suppressor genes. (ONS 2006) That’s how the body keeps controlled cell division. In most cancers, the cells undergo at least four mutations, and in many cancers, mutations occur in both the proto-oncogene, making it an oncogene, as well as the tumor suppressor gene, so that there is no control of cell division.
The Cell Cycle
All cells, normal and malignant, go through a cell cycle where it divides to create two new cells.
G0 is called the resting phase; the cell is resting from the replication process. During this phase, a normal cell is functioning normally.
G1 (gap 1) is when enzymes and substrates necessary for DNA replication are created or synthesized.
S (synthesis) is the phase during which DNA is produced to prepare for cell division. Interestingly, many chemotherapy agents are effective in killing cells in this phase of the cell cycle.
G2 (gap 2) is the phase when protein and ribonucleic acid (RNA) are synthesized and the mitotic spindle is being created.
M (mitosis) is when the cell actually divides into two daughter cells.
Sometimes when the cell begins to divide, the DNA is copied incorrectly, and mutations occur. Often, the mutations do not change the message. The body has DNA repair genes that try to fix the mutations before the cell starts dividing. If the mutation can be fixed, the cell goes on to divide. If it can not be fixed, the cell is sent into programmed cell death or apoptosis. Genetic mutations can occur in any of the cell cycle phases involving replication.
Cancer Cell vs. Normal Cell
Where normal cells appear rather neat and orderly with a single small nucleus, cancer cells are irregularly shaped with a tremendous nucleus-to-cytoplasm ratio. (ONS 2006) Generally, a cancer cell’s structure and function are different from those of the parent tissue from which it originated. This phenomenon is called differentiation. The more closely a cancer cell looks and acts like a normal cell from the parent tissue, the more differentiated that cell is considered to be.
Cancer cells do not receive the signal to stop once a monolayer of cells is created. They have no contact inhibition and will continue to multiply indefinitely, unlike normal cells that stop dividing when conditions become overcrowded.
Vascular Endothelial Growth Factor
It is now known that when cancer cells divide and fabricate a malignant tumor, and the size reaches about the head of a pencil (2 mm) the tumor needs to make new blood vessels in order to procure enough nutrition. (ONS 2006) This development of fresh blood vessels is called angiogenesis and is used to get oxygen to the cells and eliminate raze. The cell secretes vascular endothelial growth factor to start the process of building blood vessels. Without this growth factor, a tumor would suffocate and die once it became too big; much like a human embryo eventually needs a placenta for its oxygenation, nutrition and ruin. Researchers are looking into inhibiting this growth as a way to cure certain types of cancer.
Tumors
Not all tumors are cancerous. Some, while irritating or in a precarious area in the body, are benign, or not cancerous. There are two main types of cancer tumors; solid tumors, and tumors within the blood, lymph or immune systems called hematologic tumors. (ONS 2006) Examples of solid tumors are skin cancers, lung cancer, breast cancer, colon cancer, prostate cancer and bladder cancer. Examples of hematologic tumors include leukemia, lymphoma and multiple myeloma.
Malignant tumors vary from one type of cancer to another. Generally they are not encapsulated so the shape of the tumor is irregular, often with finger-like projections that invade neighboring tissue. (ONS 2006) They also have an abnormal structure, which often is poorly differentiated and has the ability to migrate or spread. Not all cancerous solid masses are equal despite common cellular characteristics, which is one reason scientists have a hard time curing many types of cancer. Understanding the biology of cancer is the first step in dealing with a diagnosis. Cancer biology can be a complicated matter for some but armed with this knowledge, one can feel more in control and can go on to properly understand a specific diagnosis and prognosis.
Sources:
The Cancer Basics Course (2006);Oncology Nursing Society (ONS).
Joanne Itano & Karen N. Taoka (2005) Core Curriculum for Oncology Nursing; 4th edition. Missouri: Saunders.
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