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Cha p te r
Se v e n

Using mice for the next set of experiments, it was discovered that
TGF prompts breast cancer cells to make a second cytokine, known
as angiopoietin-like 4 (ANGPTL4), which enhances the ability of the
cancer to spread to the lungs through the blood circulation. The
results show that the breast cancer cells use ANGPTL4 to break down
the thin capillaries of the lung, thus facilitating their escape into the
lung tissue.
TGF enhances human breast cancer metastasis and reveals how
tumor cells learn to exploit cytokines by making them work as a relay
system to promote the spread of breast cancer. The researchers are
currently seeking to determine whether TGF and ANGPTL4 may also
be active in other types of tumors, and are evaluating ways to inter-
fere with the action of these cytokines to prevent metastasis in cancer
patients. Deciphering how cancer cells take advantage of these
cytokines is essential for developing therapies that can prevent this
process since cytokines that act outside of cells can be more easily
targeted by drugs that block their activity.
The study provides support for developing agents that interfere
with TGF in order to prevent and treat cancer metastasis. It points at
ANGPTL4 as a possible target to interrupt the TGF stimulus of metas-
tasis without interfering with the molecule’s beneficial effects. Sev-
eral pharmaceutical companies are currently testing TGF-blocking
compounds in clinical trials as candidate drugs against breast cancer,
melanoma, and other types of cancer.

7.18 On-Line Measuring and Monitoring
of Gas by Spectroscopy
An optical spectrometer or optical filtering unit is often required
for chemical sensors because the spectral characteristics of absorbed,
fluorescent, or reflected light indicate the presence, absence, or
precise concentration of a particular chemical species (Fig. 7.36).
Sensing of chemical parameters via fibers is usually done by mon-
itoring changes in a suitably selected optical property—absorbance,
reflectance, scattering (turbidity), or luminescence (fluorescence or
phosphorescence), depending on the particular device. Changes in
parameters such as the refractive index may also be employed for
sensing purposes. The change in light intensity due to absorption is
determined by the number of absorbing species in the optical path,
and is related to the concentration C of the absorbing species by the
Beer-Lambert relationship. This law describes an exponential reduc-
tion of light intensity with distance (and also concentration) along
the optical path. Expressed logarithmically,

A = log I / I = η lC
0