involving near-infrared light.

Photoimmunotherapy uses an antibody to which

a photoabsorbing chemical is attached.

The antibody–photoabsorber conjugate is injected

into a patient.

It will travel through the bloodstream and eventually

reach the site of the tumor.

The conjugate will then leak out of permeable vessels

near the tumor.

It will bind to special receptors on the surface

of cancer cells.

Once the conjugate is bound to cancer cells,

the photoabsorbing chemical can be specifically activated

by near-infrared light.

When the chemical has been activated,

it causes immediate damage to the cell membrane.

Water that is outside of the cell rushes into it,

causing the cell to swell.

Nearby cells without the the special receptors

will not be affected.

Increased pressure within the swollen cell causes the

membrane to burst, releasing intracellular contents such as

proteins, DNA and RNA.

The cell then becomes smaller and shrunken in shape,

a process known as necrosis.

After treatment, the cell necrosis causes the tumor

to shrink, creating spaces between the cells.

The tumor will die and normal tissue will regrow

in its place.

Photoimmunotherapy is a new form of cancer therapy that is

highly specific for cancer cells and does not damage

nearby normal cells.

It is currently in clinical trials in patients with

inoperable tumors.