Very active cells - need lots of nutrients and therefore blood
Cancer cells develop more blood cells and an increased blood supply to help “feed” the tumor
Disorganized & Uncontrolled growth
cancer cells divide to form a growth or tumor which invades and destroys neighboring tissue at an alarming speed
Cells are not specialized and non-functional
d. LACK OF CONTACT INHIBITION
normal cells exhibit contact inhibition-they can not divide when isolated from one another…cell communication is essential for cellular reproduction & they stop dividing when they come in contact with each other
Cancer cells do not stick to each other or normal cells…they have lost all restraint and grow in multiple layers because of changes in their cell surfaces
cancer cells tend to be motile
They can dislodge themselves from a tumor and move to another area = metastasis
break loose and are transported by the blood and lymph to new sites in the body where a secondary tumor begins. The diagram below shows metastasis
Step 1 = Anaplasia
undifferentiated cell division
Disorganized & uncontrolled
Non functional cells
Step 2 = Tumor Development
Cancer cells demonstrate a lack of contact inhibition
Cells crowd together forming tumor
Step 3 = Vascularization
Blood vessels form to feed the tumor
Step 4 = Metastasis
Cells break free and travel through body
Lodge elsewhere – cancer has spread
Secondary tumors develop in new location
Self - Test
Compare and contrast normal cells with cancer cells.
Cancer Cells Normal Cells Don’t differentiate so don’t change shape as they mature Cell differentiation – cells change shape as they mature No contact inhibition – no need for directions from adjacent cells Contact inhibition – cell recognition is needed for cell reproduction Don’t stick - metastasis Adhere to each other Abnormal nuclei Normal nuclei Non-specialized Specialized to do a ‘job’ Divide uncontrollably Divide to replace damaged cells Do not die Finite life span
PROTO-ONCOGENES VS. ONCOGENES
Oncogenes are cancer-causing genes
When they are in their non-cancerous state they are called proto-oncogenes
Proto-oncogenes can be transformed into oncogenes by initiators (mutagens)
Several steps necessary – having gene doesn’t mean you will definitely get cancer
Ex. Breast cancer gene
INITIATORS VS. PROMOTERS
Genetic inheritance may predispose some people to certain types of cancer, but there must be initiation and promotion.
Initiation = proto-oncogene is converted to an oncogene by an initiator (a substance that causes a mutation = mutagen). mutagens cause changes in the DNA. Ex’s Xrays, UV rays)
Promotion = when a promoter causes the oncogene containing cell to start dividing…it speeds up the expression of the effects of the mutation.
The DNA-damaged cell has to multiply, become a tumor, and then become stimulated by the promotor. Asbestos from brake linings is the initiator (mutagen), and people who smoke cigarettes (the smoke is the promoter) are more likely to get cancer.
HOW VIRUSES CAN CAUSE CANCER
Virus may have picked up an oncogene when it reproduced in a previous host. It may pass this on to its new host.
Many cancer causing viruses are retroviruses - when they enter a cell,they make a copy of their own DNA and insert its into the host’s DNA. This changes the DNA of the host and can disrupt and turn on or off crucial genes. This may cause cancer.
In the diagram below the viral DNA at the top of the diagram is inserted at site 4 and the resulting oncogene shown below is produced.
Cancer Self-Test Questions
1. What is the definition of Metastasis
2. List the seven danger signals that may indicate the presence of cancer
3. What is the definition of a proto-oncogene
4. What is the definition of an oncogene
5. What is the definition of vascularization
6. What is the definition of an initiator
7. What is the definition of an promoter
8. What is the definition of carcinogenesis
Cancer Self-Test Questions
1. Outline the roles of initiators and promoters in carcinogenesis
2. Describe how a virus can bring about carcinogenesis
3. Describe Cancer with respect to
a. abnormal nuclei
b. disorganized and uncontrolled growth (anaplasia)