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.