Prelude to Cancer
3. Explain how mutations contribute to errors in cell cycle regulation and cancer.
Reminder: Midterm 2 is on Monday Nov. 9th, be on time (FYI: Wed Nov 11 is a
Readings for next week: Chapter 8: 97-205, 206-208
Reading Quiz due Fri Nov. 13th
Mutations in genes which regulate the cell cycle could lead to cancer.
Proto-oncogenes: genes which stimulate cells to divide under certain circumstances in normal
cells eg. genes which allow cells to pass through the G1 checkpoint
Mutations in these genes could cause cells to divide all the
time…if this happens then the mutant genes are called
oncogenes (from Greek ogkos = tumour, mass) See Fig.
5.12 (left )
tumour*-supressor genes: genes which inhibit cells from
dividing and/or cause cells to die
eg1. gene which could normally keep cells in G0
eg2. gene which causes cells with badly damaged DNA to die,
such as p53
Mutations in tumour-suppressor genes could also cause cells
to divide all the time.
*Note: In Canada we spell tumour with a u. Our textbook was written in USA.
Cancer (unregulated cell division) often requires mutations in more than one gene (as shown in
the example on the next page.)
Mutations that occur to cell-cycle control genes like the receptor on the outside of the cell (proto-
oncogene) and repair protein in the nucleus (tumour suppressor gene) can lead to cancer as shown in
the example below.
The DNA damage must have resulted in a mutated gene which allows unanchored cells to divide (Normal
cells must be anchored onto other cells or some solid surface in order to divide)
Remember that at any abnormal cells, even those with irregular cell division patterns can be recognized
by your immune system and destroyed. QUESTION: 1.What cells do this?
From mutation to cancer
1) One mutation may cause an accelerated rate of cell division. The cells are small and irregular in
shape and lack features for specialized functions. These cells are also more susceptible to coding errors
during rapid replication.
2) The tight cluster of cells forms a polyp or small benign tumor. These tumors are lumps of
3) Secondary mutations must occur to the same cells further removing any limitations on cell division
and inhibitions such as anchorage dependency. (Normal cells must be anchored onto other cells or some
solid surface in order to divide) Many conditions require four to six distinct mutations to develop into
Development of polyps in the colon as a prelude to cancer.
4) Tumour cells that slough off and enter the blood or lymph system migrate and invade other organs or
tissues. Tumours that develop at secondary sites are referred to as malignant. The tumours begin to
crowd other functional tissues, exerting pressure and diverting resources (nutrients). Often blood
vessels are stimulated to grow around the tumour, increasingly diverting nourishment from functional
tissues. Blood vessels may rupture causing internal bleeding. Starved and compressed organs may begin
to fail, causing severe pain and eventually death.
Most forms of cancer are caused by exposure to mutagens and require multiple mutations in the
same cells (somatic mutations). Only rare forms of cancer are passed on through inherited cells
(eggs and sperm – the germline).
Incidence of cancer
There are more than 200 types of cancer. US figures demonstrate that while some cancers are declining
other forms are increasing at an alarming rate.
QUESTION: 2.Why did lung cancer increase rapidly since the 1950’s for men and only started
increasing in the mid 1960’s for women?
Responding to cancer
1) Surgical removal of tumours – most effective for benign tumors
2) Radiation therapy – targeted at specific cancerous cells but destroys DNA in all cells
3) Chemotherapy – drugs that disrupt the cell cycle and stop the cells from dividing. Although the drugs
may be specific to one step of the cell cycle all cells including normal cells are affected.
QUESTIONS: 3.Why do people often feel nauseous after chemotherapy?
4. Skin cancer is often caused by excessive exposure to solar radiation. What treatment would be
advisable for an abnormal patch of skin that may form into cancer?
Risk factors are those conditions we encounter or behaviours that have been shown to cause
Avoidance of mutagen risk factors – BIG QUESTION: 5.What can you do?
Further Questions for you to consider:
6. Why is having a healthy immune system one of the best ways of avoiding cancer?
7. Smoking introduces carcinogens into the lungs on a regular basis. What advice would you give a
friend that is a smoker? And what would you tell them if they were also a regular consumer of alcoholic