Biomedical Engineering Reference
In-Depth Information
populations without starvation. It also allows cells to find their way into the cir-
culation and lymphatic system and spread to other parts of the organism. What is
not clear is whether these types of mutations are the result of selective pressure
or the simple result of an intrinsically unstable genetic system (see §3.2, above).
3.7. Evasion of Enemies during Growth and Expansion
At every level in its life, the cancer cell, and its daughter clones, must evade
the immune system. The immune system is a remarkably adaptable system that
seeks out and destroys foreign and harmful agents within the organism. Cancer
cells have developed several ways to evade this immune system surveillance
(35). In fact, in some ways, it appears that cancer cells flourish in lymph nodes,
the waystations for the white blood cells that the body uses to fight infection and
foreign bodies. The first question of every cancer evaluation is whether the can-
cer is in nearby lymph nodes? How it survives in this hostile environment is
unclear. Many cancer cells have lost the proteins (antigens) on their cell surface
that allow the body to recognize them as foreign. Other cancer cells secrete such
cytokines as transforming growth factor beta (TGF
), which inhibits the func-
tion of immune system cells (36).
3.8. Successful Colonization (Successful Metastasis)
All of the acquired mutations, whether acquired through selective pressure
via adaptation to continued hostile environmental hurdles or by chance
accumulation, result in a cancer cell clonal population that successfully
metastasizes and grows in multiple new organ sites (4,30,37). This clearly
resembles colonial expansion, and if the cancer was a set of thinking individuals,
this is what one would expect. A final required trait is the ability to survive and
flourish in new environments. This requires adapting to use the growth factors
that the new environment is rich in. For example, prostate cancer cells grow well
in the bone marrow, partly because transferrin is a potent growth factor for them
and is present in high amounts in the bone (38).
4.
MODELING CANCER AS A COMPLEX ADAPTIVE
SYSTEM AT THE LEVEL OF THE CELL
Cancer cells acquire the multiple traits necessary to survive within the
greater macroenvironment of the host. We can also model the tumor, i.e., the
collection of cancer cells, as acting in concert to function as a complex adaptive
system—one that exhibits emergent properties (see Table 3). In this model, the
individual cancer cells act as individual agents of the complex adaptive system
(6,39-41). Each cell can act independently, but may also interact to create the
tumor with the resultant properties.
