Biomedical Engineering Reference
In-Depth Information
4.2. Genes Are the Building Blocks that Cell Structure and
Function Is Based on
The six feet of DNA molecule that is present within each cell is segmented
into genes that encode the proteins that interact with each other to form the
structure and function of the cell (12). In normal cells, this structure and func-
tion is tightly controlled. In cancer, however, mutation leads to abnormal cellu-
lar functions and structural abnormalities. For a further discussion of the
importance of linking cell structure to function, see chapter 2.1, by Huang, Sul-
tan, and Ingber (Part III, this volume).
4.3. Cells with Similar Adaptive Mutations Aggregate into
Clonal Populations
There is no question that the transformation of a normal cell to a cancer can
be viewed as an evolutionary process and that the tumor can be viewed as a
separate species (1-6,11,17,44). With the realization that a single tumor is an
assembly of heterogeneous cells, it seems more appropriate to view each clonal
population within the tumor as a different species (23,41,45). The members of
each clone have a unique karyotype, morphology, and evolutionary fitness
within the context of the global ecosystem: the human body. In this system, a
tumor is a local ecosystem in which various species, clones, are in competition.
As each tumor grows, it is a collection of clones that live and die. Each cubic
centimeter of tumor (one gram) contains a billion individuals within it. If one
assumes no death, this is equivalent to 35 generations from one aberrant cell.
After ten more generations, these billion individuals have increased to a trillion.
The population of a single tumor, therefore, surpasses the population history of
mankind on the planet. The clone, or clones, that survive this growth are the
most fit, and can spread (i.e., metastasize) to other local ecosystems (i.e., other
organs). Their "success" eventually leads to a global ecological disaster: host
death. Carcinogenesis is simply the act of speciation and the populating of the
human global ecosystem.
4.4. Cancer Cells Acting in Concert Produce Properties
with Growth Advantages
A primary tumor is a collection of cells that maintain contact and communi-
cation with cellular heterogeneity. Therefore, although only a single tumor may
exist, it may be subdivided, on a cellular level, into separate populations (the
clones). For these cells or clonal populations to survive, they must exert proper-
ties to help each other survive. A good example of this is the stimulation of new
blood vessel growth (neoangiogenesis), which results in the sprouting of new
blood vessels to the tumor, with subsequent nutrient flow to a growing tumor
mass that would otherwise starve.
