T. Cancer Flashcards
contain predetermined, undifferentiated stem cells.
• Predetermined stem cells give rise to mature cells of the type of tissue where they reside.
• Cancer cells respond differently from normal cells to intracellular signals regulating equilibrium.
– Divide indiscriminately
Stem cell theory
- Loss of intracellular control of proliferation results from mutation of stem cells.
- DNA is substituted or permanently rearranged.
- Once mutated
- Cells can die from damage or by initiating programmed cellular suicide (apoptosis).
- Can recognize damage and repair itself
- Can survive and pass on damage to two or more daughter cells
- Surviving mutated cells have potential to become malignant.
Normal Cellular Differentiation
- Orderly process progressing from a state of immaturity to a state of maturity
- Stable and will not change
Proto-oncogenes
- Regulate normal cellular processes such as promoting growth
- Genetic locks that keep cells functioning normally
- Mutations that alter their expression can activate them to function as oncogenes
- When this lock is “unlocked,” as may occur through exposure to carcinogens or oncogenic viruses, genetic alterations and mutations occur.
- For example, some cancer cells produce new proteins, such as those characteristic of the embryonic and fetal periods of life. These proteins, located on the cell membrane, include carcinoembryonic antigen (CEA) and α-fetoprotein (FP).
Tumour suppressor genes
- Suppress growth
- Function to regulate cell growth
- Suppress growth of tumours
- Are rendered inactive by mutations
- Result in loss of suppression of tumour growth
- Examples of tumour suppressor genes are BRCA-1 and BRCA-2.
- Another tumour suppressor gene is the APC gene. Alterations in this gene increase a person’s risk for familial adenomatous polyposis, which is a precursor for colorectal cancer.
Benign Tumors
- Well differentiated
- Usually encapsulated
- Expansive mode of growth
- Characteristics similar to parent cell
- Metastasis is absent.
- Rarely recur
Malignat Tumors
- May range from well differentiated to undifferentiated
- Able to metastasize
- Infiltrative and expansive growth
- Frequent recurrence
- Moderate to marked vascularity
- Rarely encapsulated
- Becomes less like parent cell
Stage 1: Initiation of cancer
- Mutation of cell’s genetic structure
* Once initiated, mutation is irreversible.
Chemical carcinogens
- Long latency period makes identification of carcinogens difficult.
- Animal studies may not apply to humans.
- Certain drugs have been identified as carcinogens.
- can be known chemicals, drugs, or other products used in everyday life. Almost 30% of cancers in North America are associated with tobacco use, making tobacco the most preventable source of chemical carcinogenesis
Radiation carcinogens
- Ionizing radiation can cause cancer in almost any human tissue.
- Dose of radiation needed to cause cancer is unknown.
- Ultraviolet radiation is associated with melanoma and squamous and basal cell carcinoma.
Viral carcinogens
- Hepatitis B and C viruses, associated with hepatocellular carcinoma
- Human papillomavirus, associated with squamous cell carcinomas such as cervical, anal, and head and neck cancers
- Helicobacter pylori and gastric/duodenal ulcers, as well as of some gastric cancers
Stage 2: Promotion
- Characterized by reversible proliferation of altered cells
* Activities of promotion are reversible.
Latent period
- May range from 1 to 40 years
* Length of latent period associated with mitotic rate of tissue of origin and environmental factors
Stage 3: Progression
- Characterized by
- Increased growth rate of tumour
- Invasiveness
- Metastasis
- Most frequent sites of metastasis are lungs, brain, bone, liver, and adrenal glands.
Metastasis
the development of secondary malignant growths at a distance from a primary site of cancer.
