1

Tumor Formation• Sometimes the normal

control of mitosis in a cell fails

• This cell divides into two

• The two daughter cells divide to form four cells

• Repeated divisions soon produce a mass of cells called tumor

• This can happen in any organ

• Tumors can grow to a large size and can spread to other parts of the body

• The diseases caused by the growth of tumors are called cancer

2

Normal and Breast Cancer Mammogram

3

Some cancer cells have the ability to travel or “metastasize”

4

primary and secondary cancers

5

Control of the Cell Cycle

• cell cycle proceeds on it’s own clock, but is regulated at certain checkpoints

6

breast cancer cell

• cells can become cancerous for several reasons:

- damage to DNA

- environmental exposure toxins; examples: *PCB’s--polychlorinated

biphenyl*DDT--dichlor-diphenyl-

trichlorethylene

- other cell control issues

- damaged proteins

- genetic factors

7

How do cells know when to stop dividing?

contact inhibition

• cancerous cells have lost this inhibition

8

Features of cancer cells

cell shape is easily

distinguished from normal, healthy cells

cancerous cells lose

their attachment

to neighboring

cellscancer cells may

have an unusual # of chromosomes

cancer cells can go on dividing indefinitely, if they have an unlimited supply of nutrients they are said to be “immortal”

metabolism may be drastically altered and the cell stops functioning in a constructive way

9

Oncogenesis, proto-oncogenes and tumor suppressor genes

There are two types of genes necessary for normal control of cell division:

1. proto-oncogenes (start cell division and are essential for normal cell development)

2. tumor suppressor genes (switch off cell division)

Oncogenes: these arise when these cell cycle control genes become mutated -- these mutations lead to uncontrolled cell division

Ex: many cancers are initiated when there are mutations in tumor-suppressor genes

p53 : this tumor suppressor gene encodes for a protein that halts the cell cycle so that DNA can be repaired before division