Minimal residual disease and circulating tumor cells in breast cancer
Michail Ignatiadis
0
Monica Reinholz
1
0
Medical Oncology Department and Breast Cancer Translational Research Laboratory, Institut Jules Bordet
,
121 Boulevard de Waterloo, 1000 Brussels
,
Belgium
1
Department of Laboratory Medicine and Pathology, Mayo Clinic
,
Rochester, MN 55905
,
USA
Tumor cell dissemination in bone marrow or other organs is thought to represent an important step in the metastatic process. The detection of bone marrow disseminated tumor cells is associated with worse outcome in early breast cancer. Moreover, the detection of peripheral blood circulating tumor cells is an adverse prognostic factor in metastatic breast cancer, and emerging data suggest that this is also true for early disease. Beyond enumeration, the characterization of these cells has the potential to improve risk assessment, treatment selection and monitoring, and the development of novel therapeutic agents, and to advance our understanding of the biology of metastasis.
-
Introduction
Breast cancer (BC) is the most common cancer in women
in Europe [1]. Despite surgery and adjuvant systemic
therapy, many women with early BC still relapse and die
of their disease. Minimal residual disease (MRD) after
potentially curative surgery for BC is thought to
contribute to disease relapse and to be the target of adjuvant
treatment. MRD is defined as micrometastatic cells
undetectable by conventional imaging and laboratory
tests. Surrogates of MRD are tumor cells detected in the
bone marrow (disseminated tumor cells (DTCs)) and
peripheral blood (circulating tumor cells (CTCs)) [2]. The
detection and characterization of DTCs/CTCs are
expected to lead to personalized treatment strategies and
accelerate the development of novel therapeutic agents
for BC [2]. Furthermore, genotypic and phenotypic
characterization of DTCs/CTCs at the single cell level
Antibody-based assays
Since there are no universal tumor-specific antigen/
genes, epithelial-specific antigens, including cytokeratins
(CKs), epithelial cell adhesion molecule (EpCAM), and
growth factor receptors (for example, human epidermal
growth factor receptor (HER2)), have been used as
markers of choice for the detection of DTCs/CTCs. In
consensus meetings, the use of appropriate staining
controls, directly labeled fluorescent monoclonal
antibodies, identification of DTCs/CTCs based on
cytomorphologic criteria/phenotypic features, and validation
by two independent observers have been suggested as
measures to reduce false-positive results [8,9].
CellSearch (Veridex, Warren, NJ, USA) is an
automated enrichment and immunostaining system for CTC
FDA approval Reference
Microfluidics. Enrichment based on
physical properties
Depletion of CD45+ cells
Microfluidics. EpCAM-coated microposts
RBC lysis, CK+, EpCAM+ enrichment
Fiber-optic array scanning technology (FAST)
Collagen adhesion matrix (CAM) assay
Invasion and digestion of cell adhesion
Single gene or multi-marker RT-PCR assays
Multiparameter flow cytometry
MUC1+ and EpCAM+ enrichment
Ficoll or EpCAM+ enrichment or
depletion of CD45+ cells
HER2, MUC1 and EpCAM
CK19, MGB1, HER2, MUC1 mRNA
EpCAM+/CK8, 18,
19+/CD45CK, cytokeratin; EpCAM, epithelial cell adhesion molecule; FDA, Food and Drug Administration; HER, human epidermal growth factor receptor; MGB1,
mammaglobin-A; MUC1, mucin 1; RBC, red blood cell. aApproval as an aid in monitoring patients with metastatic breast, colorectal and prostate cancer.
detection that uses microscopic ferrofluids coated with
an antibody against EpCAM to magnetically separate
epithelial cells from whole blood [10]. Captured cells are
stained with antibodies specific for cytokeratins 8, 18 and
19 (pan-CK) and CD45 (specific for leucocytes) and
stained with 46-diamidino-2-phenylindole-2 (DAPI; to
confirm the presence of a cell nucleus). A CTC is defined
as a cell staining for pan-CK and DAPI, but not for CD45.
Currently, CellSearch is the only technology that has
received US Food and Drug Administration (FDA)
approval for CTC detection as an aid in monitoring
patients with metastatic breast, colorectal and prostate
cancer [10-12]. The performance of CellSearch for CTC
detection in metastatic solid tumors has also been
validated in ring studies [13,14].
Other technologies include the MagSweeper, which
uses immunomagnetic separation and gently enriches
target cells by 108-fold from blood, eliminating cells that
are not bound to magnetic particles [6]. This process has
been shown to keep cell function intact and not to
perturb rare cell gene expression [6]. CTCs have been
also detected using multi-parameter flow cytometry, and
their detection with this technology was associated with
poor outcome in women with BC [15]. MAINTRAC,
another method, detects circulating epithelial tumor cells
from whole unseparated blood, and uses a laser scanning
cytometer after staining with anti-human epithelial and
anti-CD45 fluorescent antibodies [16]. This technology
results in CTC counts up to 105 per milliliter of blood (...truncated)