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origin of multiple tumors existing in the same person.” While the
presence of CTCs has been reported for over 100 years, their isola-
tion and characterization have been impeded by their relative rarity
in peripheral blood with levels of approximately one CTC within
106 –10^7 leukocytes [ 1 , 2 ].
Circulating tumor cells (CTCs) are cancer cells that shed into
the blood vessels adjacent to cancer and are later carried around
the body via circulation. Although it is a direct method of detect-
ing the cancer cells in the blood, detection of CTCs is not in clini-
cal use at moment for many cancers including esophageal cancers.
Recent technological advancements in cellular and molecular biol-
ogy have allowed researchers to investigate the characterization of
CTC and its subsequent use as a prognostic and diagnostic clinical
tool. In addition, as a “liquid biopsy,” CTC detection is a less inva-
sive way to evaluate the prognosis and response to chemotherapy
in cancer patients than an endoscopic biopsy of metastatic cancer
in sites difficult to be biopsied. Several studies have reported that
CTCs can be used as prognostic and predictive markers in patients
with lung, colon, breast, or prostate cancer [ 3 , 4 ].
The prognostic and clinical implications of CTCs in esopha-
geal carcinomas are limited in Western populations where adeno-
carcinomas are highly prevalent compared to squamous cell
carcinomas [ 5 ]. The number of CTCs in peripheral blood has
shown significant correlations with poor prognosis among cancer
patients signifying its potential role in predicting cancer progres-
sion [ 5 , 6 ]. Thus, detection and studying the clinical significance
of CTCs in esophageal adenocarcinomas will help in improving the
prognosis and clinical outcome of these patients. This chapter will
review the biology and clinical implications of CTCs in esophageal
adenocarcinomas and will lay out the experimental workflow to
isolate and characterize CTCs.The distinct biological characteristics of CTCs will allow these cells
to leave primary tumor site and follow dissemination pathways to
reach distant organs or sites and in turn adapt to different tissue/
fluid microenvironments [ 7 , 8 ]. In the literature, there are no pre-
cise details of the morphological characteristics of CTCs. A recent
study has used a porous membrane filter to capture CTCs and
stained them using a special staining technique called May-
Grünwald method [ 9 ]. The captured CTCs have a relatively big
nucleus (>10 μm) and prominent nucleoli reflecting its high tran-
scriptional activity and potential to survive under different in vitro
conditions (Fig. 1 ). In live cultures, CTCs hardly grow in full con-
fluence and they usually survive up to 14 days. The occurrence of
these cells is remarkably rare and is dependent on the cell popula-
tion of the tumor. The various genetic and epigenetic changes in
CTCs will make these cells as a subpopulation of heterogeneous
cells [ 10 ].1.1 Biology of CTCs
Vinod Gopalan and Alfred K. Lam