Cytokinesis is defined as the actual point at which division of the cytoplasm occurs, creating two new cells.
At this point, the mitotic spindle is disassembled and two new nuclei form; one nuclei for each set of chromosomes. Following that, nuclear membranes reappear.
When cells don’t divide properly, abnormal cellular growth processes go awry, creating cancer.
■Abnormal Cell Division
Cancer is defined as the abnormal growth of a single cell or group of cells that have lost their ability to control their growth. A malignant cancer cell can appear in any tissue or organ in the body. As that cancer cell develops, grows, and then multiplies, it forms a mass. This mass of cancerous tissue is called a tumor.
Figure 2-11 Abnormal cell development.
Tumors can attack, invade, and then destroy adjacent tissues that are otherwise normal and healthy. Tumors, in most cases referring to abnormal growth or masses, are either classified as cancerous (malignant) or noncancerous (benign). Cancer cells that migrate from their initial point of origin can spread through a number of ways through the body. This is known as metastasizing.
Development of cancer cells
A normal and healthy cell can turn into a cancerous cell through a molecular process known as transformation. Transformation occurs in steps that include:
•Initiation
•Promotion
Figure 2-12 Skin cancer.
Initiation occurs when an alteration in the genetic material of the cell occurs. This alteration can be triggered in the chromosomal structure or the DNA. This will cause the cell to become cancerous or “abnormal”. The alteration of cellular genetic material is typically caused by carcinogens, or environmental agents, or spontaneously. The most common carcinogens that contribute to cancerous growth include:
•Tobacco
•Over-exposure to sunlight
•Radiation
•Chemicals
Not everyone is susceptible to carcinogens. For example, a smoker may never develop lung cancer, although a non-smoker can. In many cases, it’s a matter of genetics as to whom is more susceptible to carcinogens.
Promotion defines the latter step of cancerous development. Any agent that triggers promotion is called a promoter. In many cases, these are environmental substances or even drugs. Unlike carcinogens, a promoter doesn’t necessarily cause cancer all by itself, but it will “promote” or enable a cell that has undergone initiation to develop into a cancerous cell. Some cancers develop without the influence of promotion.
Cancers can develop and grow by spreading directly into adjacent tissues or organs. It can also travel great distances within the body through the lymphatic system, which is the more typical in metastatic cancers.
As an example, breast cancer typically migrates (metastasizes) into the lymph nodes nearby, and through the lymph, spreads through the body.
Cancers can also spread through the bloodstream, typical of most sarcomas.
■Different Types of Cancer
Malignant cancers are typically divided into either blood-forming tissue (such as lymphoma or leukemia) or a solid tumor such as with sarcoma or carcinoma.
Cancers such as those that form in the blood or blood-forming tissues such as lymphomas or leukemias don’t form a mass or lump, but often remain as individually separated abnormal cells. However, they multiply to a point where they can overcrowd or overcome normal blood cells in the bloodstream or bone marrow. Over time, the number of damaged or abnormal cancerous cells gradually overcome and replace healthy cells.
A carcinoma is defined as a cancer of epithelial cells. Carcinomas also affect endocrine glands or any gland that secretes hormones. Some of the most common types of carcinomas include:
•Skin cancer – such as melanoma
•Stomach cancer
•Lung cancer
•Prostate cancer
•Colon cancer
Carcinomas are more commonly found in older individuals than younger individuals.
Sarcomas are defined as cancers of muscle dermal cells or the cells that form connective tissues and muscles.
This type of cancer can form in smooth muscles found in digestive organs (Leimyosarcoma) or in bone cells, resulting in bone cancer (osteosarcoma).
This type of cancer is more commonly found in younger people than older people.
A number of factors can contribute to an increased risk of developing cancer:
•Genetics
•Environment
•Diet
•Geography
| Men | Women |
| Prostate | Breast |
| Lung | Lung |
| Colon and rectum | Colon and rectum |
| Bladder | Uterus |
| Non-Hodgkin’s lymphoma | Non-Hodgkin’s lymphoma |
Some cancers are often gender specific. For example, see the list above. Other causes of cancer include viral infections and inflammatory diseases.
Body defenses against cancer
The body’s immune system is the front line of defense against a cancerous cell. In most cases, it is believed that the immune system is able to recognize the development of common abnormal cell structures and destroy them before they can reproduce or replicate and spread.
Figure 2-13 Different types of Sarcoma.
However, cancers are not limited to individuals with compromised immune systems or system function. Otherwise healthy individuals with strong immune systems may also develop cancers.
When the body senses a cancerous or abnormal cell, it responds to tumor antigens. Antigens are described as a foreign substance that is quickly recognized by the immune system and targeted for destruction. While antigens are typically found on all cellular surfaces, the body’s immune system doesn’t typically react to its own cellular structures. However, when the cell becomes cancerous, new or previously unknown antigens appear on the surface of that cell.
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