Fluid Biopsy for Solid Tumors: A Patient’s Companion for Lifelong Characterization of Their Disease

Abstract

Cancer is currently diagnosed and treated based on the results of a tissue biopsy of the primary tumor or a metastasis using invasive techniques such as surgical resection or needle biopsy. New technology for retrieving cancer cells from the circulation, developed in the last 5 years, has made it possible to obtain a ‘fluid biopsy’ from the bloodstream without the need for an invasive procedure. This technological development makes it possible to diagnose and manage cancer from a blood test rather than from a traditional biopsy. It also allows the repeated sampling of cancer cells from a patient, making it possible, in a practical manner, to interrogate the disease repeatedly in order to understand the mechanisms by which cancer cells evolve within a given individual. The ability to obtain cancer cells repeatedly also has the potential to substantially advance drug development by enabling early ex vivo validation of both targets and early-stage compounds, as well as creating new efficiencies in the drug development process during clinical trials.

Circulating Tumor Cell Enrichment Based on Physical Properties

“…A study of imaging CTCs after erythrocytic lysis measured the cross-sectional area of CTCs from ten stage IV prostate cancer patients to be 89 µm 2 , while that of the LNCaP cell line was measured to be 142.9 µm 2 under the same measurement conditions 73 . However, the clinical relevance of CTCs of varying sizes is unclear.…”

Biophysical technologies for understanding circulating tumor cell biology and metastasis

“…Furthermore, tumor staging did not seem to make a difference in the detection of CTCs in NSCLC (40). The major disadvantage with the HD-CTC assay, however, is the inability to analyze live cells due to the fixing of cells during processing (13).…”

“…Based on the presence of cytokeratins on tumor cells, it was shown that the detection of non-tumor specific epithelial cell mRNA transcripts, such as cytokeratin, by real-time reverse transcriptase polymerase chain reaction (RT-PCR) was sensitive and could be used to prognosticate early stage breast cancer (10,11). However, the risk of illegitimate transcription (12) of epithelial protein transcripts by nonepithelial cells rendered this approach problematic, as even low levels of illegitimate transcription in the setting of the high ratio of hematopoietic cells to tumor cells would raise enough background noise to interfere with the accuracy of the assay (13). More recently, nucleic acid based detection of tumor DNA has focused on tumor mutations that are distinct from germ cell DNA and not subject to the problem of illegitimate transcription.…”

“…As the number of cancer cells in circulating blood ranges only at around 1-1,000 cells per 10 mL, and these cells are approximately 100-1,000 fold more rare than basophils and eosinophils (13), conventional methods of cellular detection are hence inadequate. Flow cytometry has been used to enumerate CTCs (16), but the number necessary for characterization is on the order of 10 3 -10 4 , much higher than exist CTCs in peripheral blood (13).…”

“…De-differentiated and EMT cell populations are relevant to understanding cancer behavior and are important to detect, as the presence of mesenchymal markers on CTCs predicts worse prognosis than the expression of cytokeratins alone (28). Because the number of white blood cells (WBCs) dwarfs the CTC population, reliance on single-parameter enrichment techniques may reduce the overall sensitivity of the assay in the background of noise from the WBC compared with multiparameter enrichment (13).…”