Downloaded from http://gut.bmj.com/ on October 28, 2014 - Published by group.bmj.com
Gut Online First, published on October 23, 2014 as 10.1136/gutjnl-2014-307647 Commentary
Circulating tumour cells go green Robert M Hoffman Circulating tumour cells (CTCs) are being used for the prediction of disease progression and drug sensitivity for various types of cancers. Current CTC isolation depends on epithelial cell surface proteins which can therefore miss CTCs that are non-epithelial. Shigeyasu et al1 describe technology to capture, sort and characterise epithelial and non-epithelial CTCs using a green fluorescent protein (GFP)-expressing attenuated adenovirus, in which the telomerase promoter regulates viral replication (OBP-401). OBP-401 selectively labels cancer cells, including CTCs, that express telomerase, which should include the vast majority of any type of cancer cell, since cancer cells in general express telomerase.2 Shigeyasu et al isolated CTCs from patients with colon cancer using their adenoviral GFP labelling technology but have not yet tested the technology on normal patients to demonstrate specificity. This study is published in Gut.1 Shigeyasu et al1 capture, image and characterise epithelial and mesenchymal CTCs in contrast to currently used methods which depend on the epithelial cells adhesion molecule (EpCAM) for capture. After sorting the GFP-expressing CTCs, direct sequencing or mutationspecific PCR detected various mutations in KRAS, BRAF and KIT genes in epithelial, mesenchymal or epithelial–mesenchymal transition-induced CTCs using model human cancer cell lines, as well as in blood samples from patients with colorectal cancer. CTCs can have epithelial and mesenchymal characteristics. EpCAM-positive and EpCAM-negative CTCs from patients with breast cancer have been shown to have a high potential to metastasise to the lung and brain in nude mice.3 4 Cytokeratin-positive and cytokeratinnegative colorectal cancer CTCs, can have complex aneuploidy.5 This type of CTC may be highly malignant and therefore a metastasis precursor. Therefore a highly aneuploid CTC that lacks epithelial markers could be missed with current CTC capture techniques. Shigeyasu’s development of a CTC capture system that functions independently of epithelial Correspondence to Dr Robert M Hoffman, Department of Surgery, AntiCancer Inc., 7917 Ostrow Street, San Diego, CA 92111 USA; [email protected]
or mesenchymal cell markers is a major step forward for assessing sensitivity to molecularly-targeted and other types of drugs. Individualised ‘targeted therapy’ includes human epidermal growth factor receptor for trastuzumab6 7 KRAS for cetuximab and panitumumab,8 echinoderm microtubule associated protein like 4-anaplastic lymphoma kinase (EML4-ALK) for crizotinib, epidermal growth factor receptor for erlotinib and gefitinib,9 10 BCR–ABL for tyrosine kinase inhibitors.11 Shigeyasu et al demonstrate that CTCs captured by their GFP method can make these analyses in place of needle core biopsies or surgical sampling tumour specimens that involve highly invasive procedures. GFP expression in CTCs offers many advantages for their analysis. We have previously shown that GFP-expressing PC-3 human prostate cancer cells orthotopically growing in nude mice, produce viable metastatic cells in the host circulation. This is in contrast to the ectopic tumours of the same cell line, which do not produce live cells into the circulation. Upon co-injection of an equivalent mixture of isolated and cultured PC-3 GFP-CTCs and parental PC-3 red fluorescent protein (RFP)-expressing human prostate cancer cells, it was shown that the captured PC-3 GFP-CTCs have an increased metastatic propensity relative to the RFP-labelled parental cells. The orthotopic model enabled important new insights into the role of the tumour microenvironment in the production of CTCs and showed that CTCs can have increased metastatic potential compared with the primary tumour12 (figure 1). The PC-3 GFP-CTCs were then expanded in culture in parallel with the parental PC-3-GFP cell line. Both cell types were then inoculated onto the chorioallantoic membrane of chick embryos. Inoculation of embryos with PC-3 GFP-CTCs resulted in a 3–10-fold increase in brain metastasis when compared with those with the parental PC-3-GFP cells, as detected by scanning laser microscopy. This is further evidence that CTCs have increased metastatic potential compared with their parental counterparts. The chick embryo represents a rapid, sensitive, imageable assay of metastatic potential for GFP-expressing Hoffman RM. Gut Month 2014 Vol 0 No 0
CTCs with potential clinical application.13 Just as mouse models such as patientderived xenografts14 are being used to obtain clinically relevant information for individual patients, the much simpler chick embryo assay, which can be read in a matter of days, may also provide individualised patient information on the metastatic potential of CTCs in the future. GFP-expressing PC-3 CTCs were placed in three-dimensional Gelfoam culture, where they proliferated and were easily observed by GFP expression.15 The chemosensitivity of growing PC-3 GFP-CTCs was compared with that of the parental PC-3 GFP cells.16 The PC-3 GFP-CTCs exhibited a significantly increased sensitivity to cisplatin and docetaxel when compared with PC-3 parental cells, with docetaxel having the greater efficacy. A future goal, based on this study, is the culture of CTCs from patients with cancer for chemosensitivity testing,17 for improved individualised therapy using the fluorescence capture system described by Shigeyasu et al.1 GFP-expressing CTCs18 can be used for gene expression analysis by many techniques in order to obtain prognostic information and predict drug sensitivity for individualised-patient therapy. Perhaps more importantly, GFP-labelled CTCs, captured by Shigeyasu et al, can be used in in vivo models to directly determine their metastatic potential and drug sensitivity which can also be tested directly in vitro. It is to be expected that OBP-401 will become an important component of ‘companion diagnostics’ which are used to design specific therapies for individual patients with cancer in order to improve their outcome. One limitation of the assay described by Shigeyasu et al1 is that intracellular GFP adenovirus replication may kill some CTCs. Further validation would be helpful before formal clinical trials. Different CTC technologies may be appropriate for different applications, and more than one assay may be required for an individual patient. For example, assays for most accurate counting of CTCs may not be necessarily optimal for capturing and enriching CTCs for genomic or biological analysis.19 There are many new interesting developments concerning CTCs. For example, Parkinson et al’s17 review of CTC assays, includes EpCAM independent technologies. Molecular and functional characterisation of CTCs including sequencing nucleic acids of single cells20–22 have been performed with EpCAM CTC isolation technologies. Scher et al23 review various CTC capture methods, antibody-dependent and 1
Copyright Article author (or their employer) 2014. Produced by BMJ Publishing Group Ltd (& BSG) under licence.
Downloaded from http://gut.bmj.com/ on October 28, 2014 - Published by group.bmj.com
Commentary
Figure 1 Human prostate carcinoma circulating tumour cells (CTCs) have increased metastatic potential compared with their precursor. A dual-colour fluorescent orthotopic co-implantation nude mouse model of an equal number of PC-3 green fluorescent protein (GFP)-CTCs and PC-3-red fluorescent protein (RFP) parental cells was made. (A) Representative fluorescence macro-image (top panel) and microscopic fluorescence image (bottom panel) of the primary and metastatic tumours two weeks after co-inoculation of equal numbers of selected PC-3 GFP-CTCs and RFP-expressing parental PC-3 cells. Note that the metastasis is comprised of almost exclusively PC-3 GFP-CTCs and very few PC-3-RFP parental cells. (B) Representative fluorescence image of a section of the primary tumour (top panel) and a lymph mode metastasis (bottom panel). (C) The figure shows a representative culture of carcinoma cells cultivated in vitro after their isolation from the bone marrow of mice implanted with the PC-3 GFP-CTCs and PC-3-RFP parental cells. Note that bone marrow-residing carcinoma cells in the dual-colour model are derived exclusively from the PC-3 GFP-CTCs.12 antibody-independent as well as describe the use of CTCs as a biomarker in castration-resistant prostate cancer which may apply to many other cancer types.
Accepted 2 October 2014
Competing interests None.
▸ http://dx.doi.org/10.1136/gutjnl-2014-306957
Provenance and peer review Commissioned; externally peer reviewed.
Gut 2014;0:1–3. doi:10.1136/gutjnl-2014-307647
To cite Hoffman RM. Gut Published Online First: [ please include Day Month Year] doi:10.1136/gutjnl2014-307647
REFERENCES
Received 20 May 2014 Revised 5 September 2014 2
2
1
Shigeyasu K, Tazawa H, Hashimoto Y, et al. Fluorescent virus-guided capturing system of human colorectal circulating tumour cells for
3
4
non-invasive companion diagnostics. Gut Published Online First: 28 May 2014. doi:10.1136/gutjnl-2014306957 Blackburn E. Telomerases and telomerase: the means to the end (Nobel Lecture). Angew Chem Int Ed Engl 2010:49:7405–21. Baccelli I, Schneeweiss A, Riethdorf S, et al. Identification of a population of blood circulating tumor cells from breast cancer patients that initiates metastasis in a xenograft assay. Nat Biotechnol 2013;31:539–44. Zhang L, Ridgway LD, Wetzel MD, et al. The identification and characterization of breast cancer CTCs competent for brain metastasis. Sci Transl Med 2013;5:180ra48.
Hoffman RM. Gut Month 2014 Vol 0 No 0
Downloaded from http://gut.bmj.com/ on October 28, 2014 - Published by group.bmj.com
Commentary 5
6
7
8 9
10
11
12
Pecot CV, Bischoff FZ, Mayer JA, et al. A novel platform for detection of CK+ and CK− CTCs. Cancer Discov 2011;1:580–6. Hurvitz SA, Hu Y, O’Brien N, et al. Current approaches and future directions in the treatment of HER2-positive breast cancer. Cancer Treat Rev 2013;39:219–29. Pietrantonio F, De Braud F, Da Prat V, et al. A review on biomarkers for prediction of treatment outcome in gastric cancer. Anticancer Res 2013;33:1257–66. Anderson SM. Laboratory methods for KRAS mutation analysis. Expert Rev Mol Diagn 2011;11:635–42. Kwak EL, Bang YJ, Camidge DR, et al. Anaplastic lymphoma kinase inhibition in non-small-cell lung cancer. N Engl J Med 2010:363:1693–703. Maemondo M, Inoue A, Kobayashi K, et al. Gefitinib or chemotherapy for non-small-cell lung cancer with mutated EGFR. N Engl J Med 2010;362:2380–8. Cross NC, White HE, Muller MC, et al. Standardized definitions of molecular response in chronic myeloid leukemia. Leukemia 2012;26:2172–5. Glinskii AB, Smith BA, Jiang P, et al. Viable circulating metastatic cells produced in orthotopic but
Hoffman RM. Gut Month 2014 Vol 0 No 0
13
14
15
16
17
18
not ectopic prostate cancer models. Cancer Res 2003;63:4239–43. Menen RS, Pinney E, Kolostova K, et al. A rapid imageable in vivo metastasis assay for circulating tumor cells. Anticancer Res 2011;31:3125–8. Tentler JJ, Tan AC, Weekes CD, et al. Patient-derived tumour xenografts as models for oncology drug development. Nature Rev Clin Oncol 2012:9:338–50. Kolostova K, Pinterova D, Hoffman RM, et al. Circulating human prostate cancer cells from an orthotopic mouse model rapidly captured by immunomagnetic beads and imaged by GFP expression. Anticancer Res 2011;31:1535–9. Menen R, Zhao M, Zhang L, et al. Comparative chemosensitivity of circulating human prostate cancer cells and primary cancer cells. Anticancer Res 2012;32:2881–4. Yu M, Bardia A, Aceto N, et al. Ex vivo culture of circulating breast tumor cells for individualized testing of drug susceptibility. Science 2014;345:216–20. Kolostova K, Zhang Y, Hoffman RM, et al. In vitro culture and characterization of human lung cancer circulating tumor cells isolated by size exclusion from
19
20
21
22
23
an orthotopic nude-mouse model expressing fluorescent proteins. J Fluoresc 2014;24:1531–6. Parkinson DR, Dracopoli N, Petty BG, et al. Considerations in the development of circulating tumor cell technology for clinical use. J Transl Med 2012;10:138. Gasch C, Bauernhofer T, Pichler M, et al. Heterogeneity of epidermal growth factor receptors status and mutations of KRAS/PIK3CA in circulating tumor cells of patients with colorectal cancer. Clin Chem 2013;59:252–60. Heitzer E, Auer M, Gasch C, et al. Complex tumor genomes inferred from single circulating tumor cells by array-CGH and next-generation sequencing. Cancer Res 2013;73:2965–75. Lohr JG, Adalsteinsson VA, Cibulskis K, et al. Whole-exome sequencing of circulating tumor cells provides a window into metastatic prostate cancer. Nature Biotech 2014;32:479–84. Scher HI, Morris MJ, Larson S, et al. Validation and clinical utility of prostate cancer biomarkers. Nat Rev Clin Oncol 2013;10:225–34.
3
Downloaded from http://gut.bmj.com/ on October 28, 2014 - Published by group.bmj.com
Circulating tumour cells go green Robert M Hoffman Gut published online October 23, 2014
Updated information and services can be found at: http://gut.bmj.com/content/early/2014/10/23/gutjnl-2014-307647
These include:
References
This article cites 20 articles, 9 of which you can access for free at: http://gut.bmj.com/content/early/2014/10/23/gutjnl-2014-307647#BIBL
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Notes
To request permissions go to: http://group.bmj.com/group/rights-licensing/permissions To order reprints go to: http://journals.bmj.com/cgi/reprintform To subscribe to BMJ go to: http://group.bmj.com/subscribe/
Gut Online First, published on October 23, 2014 as 10.1136/gutjnl-2014-307647 Commentary
Circulating tumour cells go green Robert M Hoffman Circulating tumour cells (CTCs) are being used for the prediction of disease progression and drug sensitivity for various types of cancers. Current CTC isolation depends on epithelial cell surface proteins which can therefore miss CTCs that are non-epithelial. Shigeyasu et al1 describe technology to capture, sort and characterise epithelial and non-epithelial CTCs using a green fluorescent protein (GFP)-expressing attenuated adenovirus, in which the telomerase promoter regulates viral replication (OBP-401). OBP-401 selectively labels cancer cells, including CTCs, that express telomerase, which should include the vast majority of any type of cancer cell, since cancer cells in general express telomerase.2 Shigeyasu et al isolated CTCs from patients with colon cancer using their adenoviral GFP labelling technology but have not yet tested the technology on normal patients to demonstrate specificity. This study is published in Gut.1 Shigeyasu et al1 capture, image and characterise epithelial and mesenchymal CTCs in contrast to currently used methods which depend on the epithelial cells adhesion molecule (EpCAM) for capture. After sorting the GFP-expressing CTCs, direct sequencing or mutationspecific PCR detected various mutations in KRAS, BRAF and KIT genes in epithelial, mesenchymal or epithelial–mesenchymal transition-induced CTCs using model human cancer cell lines, as well as in blood samples from patients with colorectal cancer. CTCs can have epithelial and mesenchymal characteristics. EpCAM-positive and EpCAM-negative CTCs from patients with breast cancer have been shown to have a high potential to metastasise to the lung and brain in nude mice.3 4 Cytokeratin-positive and cytokeratinnegative colorectal cancer CTCs, can have complex aneuploidy.5 This type of CTC may be highly malignant and therefore a metastasis precursor. Therefore a highly aneuploid CTC that lacks epithelial markers could be missed with current CTC capture techniques. Shigeyasu’s development of a CTC capture system that functions independently of epithelial Correspondence to Dr Robert M Hoffman, Department of Surgery, AntiCancer Inc., 7917 Ostrow Street, San Diego, CA 92111 USA; [email protected]
or mesenchymal cell markers is a major step forward for assessing sensitivity to molecularly-targeted and other types of drugs. Individualised ‘targeted therapy’ includes human epidermal growth factor receptor for trastuzumab6 7 KRAS for cetuximab and panitumumab,8 echinoderm microtubule associated protein like 4-anaplastic lymphoma kinase (EML4-ALK) for crizotinib, epidermal growth factor receptor for erlotinib and gefitinib,9 10 BCR–ABL for tyrosine kinase inhibitors.11 Shigeyasu et al demonstrate that CTCs captured by their GFP method can make these analyses in place of needle core biopsies or surgical sampling tumour specimens that involve highly invasive procedures. GFP expression in CTCs offers many advantages for their analysis. We have previously shown that GFP-expressing PC-3 human prostate cancer cells orthotopically growing in nude mice, produce viable metastatic cells in the host circulation. This is in contrast to the ectopic tumours of the same cell line, which do not produce live cells into the circulation. Upon co-injection of an equivalent mixture of isolated and cultured PC-3 GFP-CTCs and parental PC-3 red fluorescent protein (RFP)-expressing human prostate cancer cells, it was shown that the captured PC-3 GFP-CTCs have an increased metastatic propensity relative to the RFP-labelled parental cells. The orthotopic model enabled important new insights into the role of the tumour microenvironment in the production of CTCs and showed that CTCs can have increased metastatic potential compared with the primary tumour12 (figure 1). The PC-3 GFP-CTCs were then expanded in culture in parallel with the parental PC-3-GFP cell line. Both cell types were then inoculated onto the chorioallantoic membrane of chick embryos. Inoculation of embryos with PC-3 GFP-CTCs resulted in a 3–10-fold increase in brain metastasis when compared with those with the parental PC-3-GFP cells, as detected by scanning laser microscopy. This is further evidence that CTCs have increased metastatic potential compared with their parental counterparts. The chick embryo represents a rapid, sensitive, imageable assay of metastatic potential for GFP-expressing Hoffman RM. Gut Month 2014 Vol 0 No 0
CTCs with potential clinical application.13 Just as mouse models such as patientderived xenografts14 are being used to obtain clinically relevant information for individual patients, the much simpler chick embryo assay, which can be read in a matter of days, may also provide individualised patient information on the metastatic potential of CTCs in the future. GFP-expressing PC-3 CTCs were placed in three-dimensional Gelfoam culture, where they proliferated and were easily observed by GFP expression.15 The chemosensitivity of growing PC-3 GFP-CTCs was compared with that of the parental PC-3 GFP cells.16 The PC-3 GFP-CTCs exhibited a significantly increased sensitivity to cisplatin and docetaxel when compared with PC-3 parental cells, with docetaxel having the greater efficacy. A future goal, based on this study, is the culture of CTCs from patients with cancer for chemosensitivity testing,17 for improved individualised therapy using the fluorescence capture system described by Shigeyasu et al.1 GFP-expressing CTCs18 can be used for gene expression analysis by many techniques in order to obtain prognostic information and predict drug sensitivity for individualised-patient therapy. Perhaps more importantly, GFP-labelled CTCs, captured by Shigeyasu et al, can be used in in vivo models to directly determine their metastatic potential and drug sensitivity which can also be tested directly in vitro. It is to be expected that OBP-401 will become an important component of ‘companion diagnostics’ which are used to design specific therapies for individual patients with cancer in order to improve their outcome. One limitation of the assay described by Shigeyasu et al1 is that intracellular GFP adenovirus replication may kill some CTCs. Further validation would be helpful before formal clinical trials. Different CTC technologies may be appropriate for different applications, and more than one assay may be required for an individual patient. For example, assays for most accurate counting of CTCs may not be necessarily optimal for capturing and enriching CTCs for genomic or biological analysis.19 There are many new interesting developments concerning CTCs. For example, Parkinson et al’s17 review of CTC assays, includes EpCAM independent technologies. Molecular and functional characterisation of CTCs including sequencing nucleic acids of single cells20–22 have been performed with EpCAM CTC isolation technologies. Scher et al23 review various CTC capture methods, antibody-dependent and 1
Copyright Article author (or their employer) 2014. Produced by BMJ Publishing Group Ltd (& BSG) under licence.
Downloaded from http://gut.bmj.com/ on October 28, 2014 - Published by group.bmj.com
Commentary
Figure 1 Human prostate carcinoma circulating tumour cells (CTCs) have increased metastatic potential compared with their precursor. A dual-colour fluorescent orthotopic co-implantation nude mouse model of an equal number of PC-3 green fluorescent protein (GFP)-CTCs and PC-3-red fluorescent protein (RFP) parental cells was made. (A) Representative fluorescence macro-image (top panel) and microscopic fluorescence image (bottom panel) of the primary and metastatic tumours two weeks after co-inoculation of equal numbers of selected PC-3 GFP-CTCs and RFP-expressing parental PC-3 cells. Note that the metastasis is comprised of almost exclusively PC-3 GFP-CTCs and very few PC-3-RFP parental cells. (B) Representative fluorescence image of a section of the primary tumour (top panel) and a lymph mode metastasis (bottom panel). (C) The figure shows a representative culture of carcinoma cells cultivated in vitro after their isolation from the bone marrow of mice implanted with the PC-3 GFP-CTCs and PC-3-RFP parental cells. Note that bone marrow-residing carcinoma cells in the dual-colour model are derived exclusively from the PC-3 GFP-CTCs.12 antibody-independent as well as describe the use of CTCs as a biomarker in castration-resistant prostate cancer which may apply to many other cancer types.
Accepted 2 October 2014
Competing interests None.
▸ http://dx.doi.org/10.1136/gutjnl-2014-306957
Provenance and peer review Commissioned; externally peer reviewed.
Gut 2014;0:1–3. doi:10.1136/gutjnl-2014-307647
To cite Hoffman RM. Gut Published Online First: [ please include Day Month Year] doi:10.1136/gutjnl2014-307647
REFERENCES
Received 20 May 2014 Revised 5 September 2014 2
2
1
Shigeyasu K, Tazawa H, Hashimoto Y, et al. Fluorescent virus-guided capturing system of human colorectal circulating tumour cells for
3
4
non-invasive companion diagnostics. Gut Published Online First: 28 May 2014. doi:10.1136/gutjnl-2014306957 Blackburn E. Telomerases and telomerase: the means to the end (Nobel Lecture). Angew Chem Int Ed Engl 2010:49:7405–21. Baccelli I, Schneeweiss A, Riethdorf S, et al. Identification of a population of blood circulating tumor cells from breast cancer patients that initiates metastasis in a xenograft assay. Nat Biotechnol 2013;31:539–44. Zhang L, Ridgway LD, Wetzel MD, et al. The identification and characterization of breast cancer CTCs competent for brain metastasis. Sci Transl Med 2013;5:180ra48.
Hoffman RM. Gut Month 2014 Vol 0 No 0
Downloaded from http://gut.bmj.com/ on October 28, 2014 - Published by group.bmj.com
Commentary 5
6
7
8 9
10
11
12
Pecot CV, Bischoff FZ, Mayer JA, et al. A novel platform for detection of CK+ and CK− CTCs. Cancer Discov 2011;1:580–6. Hurvitz SA, Hu Y, O’Brien N, et al. Current approaches and future directions in the treatment of HER2-positive breast cancer. Cancer Treat Rev 2013;39:219–29. Pietrantonio F, De Braud F, Da Prat V, et al. A review on biomarkers for prediction of treatment outcome in gastric cancer. Anticancer Res 2013;33:1257–66. Anderson SM. Laboratory methods for KRAS mutation analysis. Expert Rev Mol Diagn 2011;11:635–42. Kwak EL, Bang YJ, Camidge DR, et al. Anaplastic lymphoma kinase inhibition in non-small-cell lung cancer. N Engl J Med 2010:363:1693–703. Maemondo M, Inoue A, Kobayashi K, et al. Gefitinib or chemotherapy for non-small-cell lung cancer with mutated EGFR. N Engl J Med 2010;362:2380–8. Cross NC, White HE, Muller MC, et al. Standardized definitions of molecular response in chronic myeloid leukemia. Leukemia 2012;26:2172–5. Glinskii AB, Smith BA, Jiang P, et al. Viable circulating metastatic cells produced in orthotopic but
Hoffman RM. Gut Month 2014 Vol 0 No 0
13
14
15
16
17
18
not ectopic prostate cancer models. Cancer Res 2003;63:4239–43. Menen RS, Pinney E, Kolostova K, et al. A rapid imageable in vivo metastasis assay for circulating tumor cells. Anticancer Res 2011;31:3125–8. Tentler JJ, Tan AC, Weekes CD, et al. Patient-derived tumour xenografts as models for oncology drug development. Nature Rev Clin Oncol 2012:9:338–50. Kolostova K, Pinterova D, Hoffman RM, et al. Circulating human prostate cancer cells from an orthotopic mouse model rapidly captured by immunomagnetic beads and imaged by GFP expression. Anticancer Res 2011;31:1535–9. Menen R, Zhao M, Zhang L, et al. Comparative chemosensitivity of circulating human prostate cancer cells and primary cancer cells. Anticancer Res 2012;32:2881–4. Yu M, Bardia A, Aceto N, et al. Ex vivo culture of circulating breast tumor cells for individualized testing of drug susceptibility. Science 2014;345:216–20. Kolostova K, Zhang Y, Hoffman RM, et al. In vitro culture and characterization of human lung cancer circulating tumor cells isolated by size exclusion from
19
20
21
22
23
an orthotopic nude-mouse model expressing fluorescent proteins. J Fluoresc 2014;24:1531–6. Parkinson DR, Dracopoli N, Petty BG, et al. Considerations in the development of circulating tumor cell technology for clinical use. J Transl Med 2012;10:138. Gasch C, Bauernhofer T, Pichler M, et al. Heterogeneity of epidermal growth factor receptors status and mutations of KRAS/PIK3CA in circulating tumor cells of patients with colorectal cancer. Clin Chem 2013;59:252–60. Heitzer E, Auer M, Gasch C, et al. Complex tumor genomes inferred from single circulating tumor cells by array-CGH and next-generation sequencing. Cancer Res 2013;73:2965–75. Lohr JG, Adalsteinsson VA, Cibulskis K, et al. Whole-exome sequencing of circulating tumor cells provides a window into metastatic prostate cancer. Nature Biotech 2014;32:479–84. Scher HI, Morris MJ, Larson S, et al. Validation and clinical utility of prostate cancer biomarkers. Nat Rev Clin Oncol 2013;10:225–34.
3
Downloaded from http://gut.bmj.com/ on October 28, 2014 - Published by group.bmj.com
Circulating tumour cells go green Robert M Hoffman Gut published online October 23, 2014
Updated information and services can be found at: http://gut.bmj.com/content/early/2014/10/23/gutjnl-2014-307647
These include:
References
This article cites 20 articles, 9 of which you can access for free at: http://gut.bmj.com/content/early/2014/10/23/gutjnl-2014-307647#BIBL
Email alerting service
Receive free email alerts when new articles cite this article. Sign up in the box at the top right corner of the online article.
Notes
To request permissions go to: http://group.bmj.com/group/rights-licensing/permissions To order reprints go to: http://journals.bmj.com/cgi/reprintform To subscribe to BMJ go to: http://group.bmj.com/subscribe/
