circulating tumor cells in lung cancer
Friday 29 November 2013
The knowledge into the pathophysiology of the natural history of lung cancer has improved a lot through different studies concerning CTCs.
In particular, recent work performed by the team of Massagué in New York has established that CTCs can give rise not only to metastases, but can also colonize the primary tumor site and participate in primary tumor progression, through a phenomenon called tumor self-seeding.
Other studies showed that CTCs can circulate in the bloodstream of lung cancer patients as single cells or as aggregates [called circulating tumor microemboli (CTMs)]. In this regard, the phenotype of single or aggregated CTCs can be different and may present different levels of potential aggressiveness.
The diagnosis of metastases of unknown primary origin could be determined by the genomic analysis of CTCs. However, the different methods required for such a diagnosis are difficult to set up in routine clinics, and are currently probably too expensive.
Several studies have correlated the presence and the number of CTCs with worse prognosis in lung cancer patients. In early stage lung cancer, the pre-operative detection of CTCs is associated with worse disease free and overall survival (18,19). The detection of CTCs in late stage lung cancer patients and of a high persistent rate of CTCs after chemotherapy in these patients correlated with worse prognosis (15,20).
The detection of some genomic alterations present in CTCs of cancer patients can be associated with targeted therapy (21). Thus, patients with EGFR mutations or EML4-ALK rearrangements detected in CTC can potentially benefit from treatment with tyrosine kinase inhibitors or crizotinib, respectively (22,23).
Direct technologies for CTC detection can gain information concerning the morphology of the CTC. In this regard, as for cytopathology performed on smears or on fine needle aspiration, CTCs can be identified efficiently as malignant or benign cells according to the established cytological criteria.
Previous studies have distinguished different categories of CTCs in lung cancer patients according to these criteria. Thus, the so called “circulating non hematological cells (CNHC)” can show features of malignant or benign cells. Moreover, a couple of CNHC cannot be classified as benign or malignant cells and were called CNHC with uncertain features of malignancy (26). These morphological analyses are pivotal since it is possible to correlate these rare isolated cells with malignant criteria in the blood lung cancer patients.
Moreover, ICC and FISH can be performed on these CNHC to obtain better characterization of their phenotype and to detect some genomic alterations accessible to targeted therapy. ICC showed substantial heterogeneity of CTCs in lung cancer patients.
As an example, CTCs can express cytokeratin, while other cells express both cytokeratin and vimentin, and finally some CTCs with malignant features can express vimentin only. The direct methods also provide interesting data to better understand the pathophysiology of progression and dissemination of lung cancer. It has been demonstrated that these CTCs can circulate as isolated cells or as aggregates called CTMs. It seems that the presence of CTMs is a negative prognostic factor for lung cancer patients.
Interestingly, it is possible to assess the ALK status (by ICC or FISH) of CTCs isolated and characterized by ISET (17,52).
Similar approaches could potentially evaluate the EGFR, BRAF, ROS-1 or c-MET status of CTCs isolated by ISET in lung cancer patients since specific antibodies and probes targeting these molecules are now commercially available (53-57).
One current drawback is the lack of a biomarker to confirm the malignant nature of CNHCs isolated by the direct methods. Moreover, it is impossible to determine the aggressiveness and the invasiveness of these cells.
One of the major pitfalls of many indirect methods for detection of CTCs is the fact that they are based on the postulate that CTCs express an epithelial phenotype. For example the CellSearch technology, which uses anti-Epcam and anti-cytokeratins antibodies for CTC isolation, cannot detect CTCs showing epithelial-to-mesenchymal transition, a frequent process in lung cancer progression and dissemination. Thus, most of the indirect methods can give false negative results.
One of the main difficulties, when working on CTCs in the field of lung cancer, is to analyze the somatic mutations, which can be present in these cells. This is due to the fact that the quantity and the quality of the extracted DNA from the cells are low. In this regard the pre-analytical phase of DNA accessibility can have a strong impact on the quality of the DNA.
Hofman V, Ilie M, Long E, et al. Detection of circulating tumor cells from lung cancer patients in the era of targeted therapy: promises, drawbacks and pitfalls. Curr Mol Med 2014;14:440-56. [Hofman V, Ilie M, Long E, et al. Detection of circulating tumor cells from lung cancer patients in the era of targeted therapy: promises, drawbacks and pitfalls. Curr Mol Med 2014;14:440-56. [http://www.ncbi.nlm.nih.gov/pubmed/24730524]
Circulating tumor cells in lung cancer. Young R, Pailler E, Billiot F, Drusch F, Barthelemy A, Oulhen M, Besse B, Soria JC, Farace F, Vielh P. Acta Cytol. 2012;56(6):655-60. doi : 10.1159/000345182 PMID: 23207444
Hofman V, Bonnetaud C, Ilie MI, et al. Preoperative circulating tumor cell detection using the isolation by size of epithelial tumor cell method for patients with lung cancer is a new prognostic biomarker. Clin Cancer Res 2011;17:827-35. [http://www.ncbi.nlm.nih.gov/pubmed/21098695]
Hofman V, Ilie MI, Long E, et al. Detection of circulating tumor cells as a prognostic factor in patients undergoing radical surgery for non-small-cell lung carcinoma: comparison of the efficacy of the CellSearch Assay and the isolation by size of epithelial tumor cell method. Int J Cancer 2011;129:1651-60. [http://www.ncbi.nlm.nih.gov/pubmed/22591372]
Normanno N, Rossi A, Morabito A, et al. Prognostic value of circulating tumor cells’ reduction in patients with extensive small-cell lung cancer. Lung Cancer 2014;85:314-9. [http://www.ncbi.nlm.nih.gov/pubmed/24882383]
Ilie M, Long E, Butori C, et al. ALK-gene rearrangement, a comparative analysis on circulating tumour cells and tumour tissue from lung adenocarcinoma patients. Ann Oncol 2012;23:2907-13. [http://www.ncbi.nlm.nih.gov/pubmed/22735679]