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can save a patient from worsening the condition with continuously shed in the circulation. They are discontinuous
unsuitable medications. Furthermore, the earlier they and might not be present in homogenous condition.
are detected, faster and better treatment options can Thus, while isolating CTCs a single blood sample might
be made available to the patient. It provides the basis fall insuffi cient or may give inaccurate results. This is
[20]
of understanding mutations and genotypic changes of accompanied by further reduction in their numbers when
malignant cells and hence provides the best suitable they get clogged in capillaries due to their large size.
targeted therapy. CTCs are multifunctional biomarkers and They can also form clusters while fl owing and some of
enable us to assess the patient serially along the treatment them may even adhere to the walls of the capillaries, or
journey. They are potentially an alternative to invasive some might be cloaked by the platelets. Further reduction
biopsies for detection, characterization and monitoring in CTCs number takes place during batch processes
[14]
of non-hematological cancers. Although as of now it which are followed for their enrichment. Simpler methods
is not clear whether CTCs are the cause of metastasis, involve size based separation, collagen adhesion method
they still hold the potential for being a cause for disease or density-based separation. Other sophisticated ones
progression. Metastasis is better known to be caused rely on epithelial markers, immunomagnetic techniques,
by cancer stem cells (CSCs), which are highly motile, microchips, and nanotech approaches. [21]
self-renewing cancer initiators. They also have increased Density-based Ficoll-Hypaque method
resistance to apoptosis as well as to certain treatment
[22]
drugs. CTCs with such properties can be metastatic Gertler et al. 2003 have used Ficoll-Hypaque
in nature. CTCs after undergoing EMT can also make density-based separation method to separate tumor cells
non-CSC type cells to behave like CSCs. In addition, it is from bone marrow and peripheral blood aspirations.
yet to be clarifi ed whether cells with metastatic potential It is based on differential migration of cells which
have increased motility and aggressive nature of CTCs as takes places during centrifugation and gives a layered
compared to non-metastatic tumor cells. On the whole, separation of cells types. The porous barrier is permeable
CTCs give us biological insights of the disease condition, to the red blood cells and other smaller components of
progression, and treatment prediction. Reports indicate blood. The buffy coat above this layer is of concern, as it
that patients with fewer numbers of CTCs survive longer contains the tumor cells along with leukocytes. This layer
[15]
than the patients which have more number of CTCs. can be easily aspirated and analyzed further to determine
Another important implication of CTCs is that they can the presence and quantifi cation of CTCs. [21]
form the constitutional basis of tumor staging. The Immunomagnetic (antibody based) method
[16]
types and quantity of CTCs can form prima facie of the
degree and type of cancer. They can be periodically used This method exploits the presence of surface markers
to keep a check on disease progression. In some cases, on tumor cells or hematopoietic cells. In this method,
they have even been able to identify the drug targets by antibodies are coupled with magnetic particles and then
analyzing the enumerated CTCs and its phenotype. They used for positive or negative selection of CTCs. In
can even help in the selection of secondary treatment positive selection, surface markers of CTCs are targeted,
options while the patient has failed to respond to fi rst line whereas, in negative selection, depletion of blood cells
treatments. One such example is the detection of human other than CTCs is achieved by targeting their surface
[17]
[23]
epidermal growth factor receptor 2 (HER2)-positive CTCs markers as shown in Figure 3. Epithelial cell adhesion
in HER2-negative breast cancers. Thus, it gives us molecule (EpCAM) is one of the most widely tapped
[18]
hints and specks about quiescent population that may be markers on tumor cells. CD45 in case of lymphocytes
present in the tumor and be the cause of drug resistance and glycophorin for erythrocytes are two commonly
®
or relapse of the disease. Since, CTCs hold such critical used markers in case of negative selection. MACS
[19]
information about a tumor and its characteristics; they can has introduced microbeads which can be used in such
defi nitely form the pedestal of patient-specifi c treatments. negative selection. [24]
The great enigma about cancer can adjudicate with the Food and Drug Administration (FDA) has approved
help of information retrieved from CTCs analysis. CellSearch (by Janssen Diagnostics) which is by far the
®
Isolation and Analysis of CTCs most effi cacious system for extraction and enumeration of
CTCs. The CTCs according to this system are defi ned
[25]
In the recent years, CTCs have gained increasing by a characteristic round oval shape cells with nucleus
importance because of their multi potential uses. Despite which is stained by 4',6-diamidino-2-phenylindole
their long known discovery and spates in clinical oncology, stain. This procedure may be laborious and intensive
no method has been devised to isolate or enumerate CTCs but gives the best enrichment results as a comparison
effi ciently. Primarily, their quantity in blood circulation is to other existing techniques. It makes use of antibodies
the biggest hurdle in isolation of CTCs. Out of the several like EpCAM attached to magnetic beads for binding to
CTCs shed by the primary tumor only about 0.1% survives specifi c tumor cell surface receptors. These cells can be
in the circulation and only about 0.01% is responsible pulled out from the rest of cells under the infl uence of
[26]
for metastasis. It has been reported that CTCs are not a magnetic fi eld. Some tumor cells might escape the
[17]
46 Journal of Cancer Metastasis and Treatment ¦ Volume 1 ¦ Issue 2 ¦ July 15, 2015 ¦