Introduction
- All of our cells have similar structures and share a majority of their functions.
- Cancers may be categorized into five basic types based on the cell of origin:
- Carcinoma - epithelial cells
- Sarcoma - muscle, bone, cartilage, fat, or connective tissue
- Leukemia - blood cells or their precursors
- Lymphoma - bone marrow derived cells; cancer affects the lymphatic system
- Myeloma - specific blood cells; B lymphocytes (B-cells)
Stages of Tumor Progression
- Tumors typically progress is a stepwise fashion:
- Hyperplasia - cells divide too much but appear normal
- Dysplasia - the tumor cells and tissue appear abnormal
- Carcinoma in situ - tumor contains primarily altered cells and is growing larger; it has not left the site of origin
- Malignant Cancer - tumor has begun to invade nearby or distant tissues
- Benign tumors remain in their initial location and do not invade other tissues.
Initiators and Promoters
- Initiation is the first step in the two-stage model of cancer development.
- Initiators cause irreversible changes (mutations) to DNA that increase cancer risk.
- Promotion is the second step in the two-stage model of cancer development.
- Once a cell has been mutated by an initiator, it is susceptible to the effects of promoters.
- Promoters increase the proliferation of cells and there are two main types:
- Specific - interact with receptors on or in particular target cells.
- Nonspecific - alter gene expression without the presence of a known receptor
Carcinogens
- Substances which can cause cancer are known as carcinogens.
- The process of cancer development is called carcinogenesis.
- Certain carcinogenic chemicals are associated with an increased risk of specific cancers due to chronic exposure.
- One of the most potent carcinogens in humans is benzo[a]pyrene, a compound found in cigarette smoke.
Viruses and Bacteria
- Certain viruses and bacteria have also been associated with the initiation and promotion of tumor growth.
- Some viruses cause cancer directly by affecting cell division while other viruses cause cancer by causing chronic inflammation or reducing immune system function.
Chronic Inflammation
- Chronic inflammation is an important factor in tumor development.
- Inflammation can lead to altered behavior of cells, stimulation of blood vessel growth (angiogenesis) and tissue remodeling.
- Markers of inflammation correlate with a worse prognosis for cancer patients.
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