What is Cancer?What is Cancer?
Up to 10 million new cases a year worldwide
Classifies a family of diseases of unrestrained cell growth
G1
G2
S(DNA synthesis)
1 - INTERPHASE – cell growth, copying of Chromosomes
Cytoki
nesis
2 - MITOTIC(M) PHASE
Mitos
is
Phases of the Cell CyclePhases of the Cell Cycle
LE 12-14LE 12-14G1 checkpoint
G1
S
M
M checkpoint
G2 checkpoint
G2
Controlsystem
LE 12-15LE 12-15
G1
G1 checkpoint
G1
G0
If a cell receives a go-ahead signal at the G1 checkpoint, the cell continues on in the cell cycle.
If a cell does not receive a go-ahead signal at the G1 checkpoint, the cell exits the cell cycle and goes into G0, a nondividing state.
The G1 checkpoint seems to be the most important one
Stop and Go Signs: Internal and Stop and Go Signs: Internal and External Signals at the CheckpointsExternal Signals at the Checkpoints
M phase checkpoint ◦An internal signal - chromosomal misalignment
send a molecular signal that delays anaphaseSome external signals are growth factors,
proteins released by certain cells that stimulate other cells to divide
For example, platelet-derived growth factor (PDGF) stimulates the division of human fibroblast cells in culture
LE 12-17LE 12-17
Petriplate
Scalpels
Without PDGF
With PDGF
Without PDGF
With PDGF
10 mm
Another example of external signals is density-dependent inhibition, in which crowded cells stop dividing
Most animal cells also exhibit anchorage dependence, in which they must be attached to a substratum in order to divide
LE 12-18aLE 12-18aCells anchor to dish surface anddivide (anchorage dependence).
When cells have formed a completesingle layer, they stop dividing(density-dependent inhibition).
If some cells are scraped away, theremaining cells divide to fill the gap andthen stop (density-dependent inhibition).
25 µmNormal mammalian cells
LE 12-18bLE 12-18b
Cancer cells do not exhibitanchorage dependenceor density-dependent inhibition.
Cancer cells25 µm
Loss of Cell Cycle Controls in Loss of Cell Cycle Controls in Cancer CellsCancer Cells
Cancer cells do not respond normally to the body’s control mechanisms
Cancer cells form tumors, masses of abnormal cells within otherwise normal tissue
If abnormal cells remain at the original site, the lump is called a benign tumor
Malignant tumors invade surrounding tissues and can metastasize, exporting cancer cells to other parts of the body, where they may form secondary tumors
LE 12-19LE 12-19
Cancer cell
Bloodvessel
LymphvesselTumor
Glandulartissue
Metastatictumor
A tumor grows from asingle cancer cell.
Cancer cells invadeneighboring tissue.
Cancer cells spreadthrough lymph andblood vessels toother parts of thebody.
A small percentageof cancer cells maysurvive and establisha new tumor in anotherpart of the body.