Biomedical Engineering Reference
In-Depth Information
rate of some cancers, the fi nal outcome is death, due to recurrence of cancer.
The reason is (among others) in the fact that clinicians are injecting also cancer
cells with healthy stem cells during re-infusion after apheresis collection, which
accumulate and renew with a time to the critical level causing relapse or death.
Ontogeny (development of an organism) and oncology (cancer development)
share many common features. From the 1870s the connection between develop-
ment and cancer has been reported for various types of cancers [
1
]. Existence of
“cancer stem cells” with aberrant cell division has also been reported more
recently [
5
]. The connection between cancer and development is clearly evident
in teratocarcinomas. As early as 1862, Virchow discovered that the germ cell
tumor teratocarcinoma is made up of embryonic cells [
1
]. In 1970, Stevens
derived embryonic carcinoma cells from teratocarcinoma (a spontaneous tumor
of germ cells that resembles development gone awry) [
1
]. This tumor may contain
several types of epithelia: areas of bone, cartilage, muscle, fat, hair, yolk sac, and
placenta. These specialized tissues are often adjacent to an area of rapidly divid-
ing unspecialized cells. The terato-carcinomas are able to differentiate into nor-
mal mature cells when transplanted into another animal. This alternation between
developmental and tumor cells status demonstrates how closely development and
cancer are related. The present-day challenge is to decode the common molecular
mechanism and genes involved in self-renewal for cancer cells and stem cells.
The very new concept in the fi eld of cancerogenesis is the cancer stem cell (CSC)
[
5
]. Cancer stem cells share many characteristics with normal stem cells, including
self-renewal and differentiation. CSC is defi ned as “a cell within a tumor that pos-
sesses the capacity to self-renew and to cause the heterogeneous lineages of cancer
cells that comprise the tumor”. These cells have functionality allowing them the
capability of causing an invasive group of cells (tumorigenic) that create metastasis
[
7
-
11
]. There are two theories with respect to CSC entity [
11
]:
A. Stochastic/Clonal evolution Model
B. Hyerarchic/Cancer Stem Cell Model
This model states that all cancer cells hold
tumorigenic potential and they are the product of
clonal evolution by the acquisition of genetic
mutations and epigenetic changes
Tumors show hierarchy, with a
subpopulation of cancer cells having a
tumorigenic potential much greater than that
of other cancer cells
There are two well defi ned yet different models of Cancer Stem Cell within sci-
entifi c community none of which completely can describe the features of Cancer
Stem Cell:
(a)
Stochastic (clonal evolution) model
: This model states that all cancer cells
hold tumorigenic potential and they are the product of clonal evolution by the
acquisition of genetic mutations and epigenetic changes.
(b)
Hierarchical (cancer stem cell) model
: Tumors show hierarchy, with a sub-
population of cancer cells having a tumorigenic potential much greater than that
of other cancer cells. Tumor contains hierarchical organization consisting of
stem cells at top, which are cells within a tumor with the capacity to self-renew
and generate heterogeneous lineages of cancer cells, progenitors, and differenti-
ated cells which are no longer able to produce tumors (Fig.
9.1
).
