Tissue still represents the “gold standard” biosource for molecular profiling of lung cancer. However, the use of tissue samples in clinical practice is associated with several technical and biological limitations. For instance, tissue specimens can provide only a small picture of the complex molecular landscape of patients with lung cancer, freezing the situation at the moment when the tissue has been taken. Conversely, liquid biopsy, through a noninvasive and repeatable withdrawal of blood (or other bodily fluids), has the incredible capacity to allow an effective, real-time monitoring of the lung cancer evolution (e.g., early detection, responsiveness or resistance to any treatment), thus overcoming the spatial and temporal issues of tumor heterogeneity.
These peculiar characteristics make liquid biopsy an appealing tool for monitoring patients with lung cancer at multiple points, ranging from screening in high-risk populations, to early detection of recurrence after surgery, to therapeutic monitoring during anticancer therapies. At the screening stage, liquid biopsy may represent the key weapon in detection in high-risk individuals. However, it should be borne in mind that an important limitation of early detection of lung cancer using circulating free DNA is the risk of false positive results because of clonal hematopoiesis.
The identification of minimal residual disease, after a curative-intent treatment, might be another interesting field of investigation for liquid biopsy in lung cancer. Recently, some interesting studies have explored this potential novel application for liquid biopsy. By adopting a CAncer Personalized Profiling by deep Sequencing (CAPP-Seq) approach, Chaudhuri et al.2 demonstrated that 94% of patients with resected localized lung cancer and detectable circulating tumor DNA (ctDNA) in the bloodstream experienced recurrence after treatment. However, this high percentage may be related to the fact that most of the patients had stage II or III disease. In fact, an important issue when adopting liquid biopsy in the earlier stages or when particular metastatic sites (e.g., brain, bones) are involved is the limited shedding of tumoral DNA and circulating cells into the bloodstream. In advanced stages of disease, liquid biopsy plays a pivotal role in EGFR molecular assessment for treatment-naive patients when tissue is not available or when it is inadequate to conduct molecular analysis in order to administer first- or second-generation TKIs. In addition, liquid biopsy represents the first choice in a resistance setting for patients who have received first- or second-generation TKI treatment, for the detection of EGFR exon 20 p.T790M resistance point mutation in order to administer third-generation TKIs (e.g., osimertinib). In particular, in this latter setting, liquid biopsy may be useful to monitor the tumor evolution, which appears to be more heterogeneous and subclonal. In the resistance setting, ctDNA monitoring using amplicon-based, next-generation sequencing platforms may evidence the high tumor genomic complexity and heterogeneity and thus highlight the appearance of different competitive resistant clones harboring different genomic alterations.
In addition, liquid biopsy has the ability to show resistance to treatments months before clinical and radiologic progression. Besides its use in targeted therapies with TKIs, liquid biopsy may also be adopted in monitoring response to immune-checkpoint inhibitors (ICIs). Different studies have demonstrated that a high blood tumor mutational burden may positively predict response to anti–PD-1 and anti–PD-L1.
Monitoring the response to ICI administration in patients with advanced-stage NSCLC is another field of interest for liquid biopsy. Accumulating evidence suggests that reduction in ctDNA levels in the earlier phases of the treatment (1 to 2 months) may strongly predict durable response to ICIs. Conversely, persistence of high levels of ctDNA is associated with higher risk of relapse or lack of efficacy of the adopted drug regimen. In addition, early modification in blood tumor mutational burden may be useful to discriminate between pseudo-progression and true progression.
Another important field of investigation is the identification of circulating biomarkers for the detection of minimal residual disease when ICIs are adopted as adjuvant drug approaches, or for the identification of resistance mechanisms against ICIs, such as Januk Kinase 1/2 (JAK1/2) or Beta-2-Microglobulin (B2M) mutations. In addition to its utility with circulating free DNA and ctDNA, liquid biopsy has demonstrated the significant role that circulating tumor cells (CTCs) can playin providing information about intratumor heterogeneity, tumor evolution, and treatment resistance. In addition, CTCs may overcome the limit of ctDNA in the evaluation of the expression level of PD-L1. Ilie et al. highlighted a good concordance between tissue and CTCs, showing a potential role for minimally invasive CTCs in the evaluation of PD-L1 expression in patients with advanced-stage NSCLC.
Considering together all the concepts discussed here, plasma genotyping may be a useful tool from screening to treatment response monitoring for patients with NSCLC. This rapid and noninvasive approach may predict resistance to target treatments or immunotherapy regimens before clinical or radiologic evidence of progression. In addition, as demonstrated by Leighl et al. in the NILE study, plasma genotyping should be considered complementary to tissue-based genotyping, taking into account the faster turnaround time with respect to tissue analysis.
In conclusion, starting from cancer interception and screening, through identification of clinically relevant biomarkers for treatment decision making, and monitoring of minimal residual disease through ctDNA quantitative assessment with next-generation methodologies, liquid biopsy is becoming the key weapon in real-time monitoring of patients with cancer, opening the doors to a new era of precision oncology.
References:
- Guibert N, Pradines A, Favre G, Mazieres J. Current and future applications of liquid biopsy in nonsmall cell lung cancer from early to advanced stages. Eur Respir Rev. 2020; 29:190052.
- Chaudhuri AA, Chabon JJ, Lovejoy AF, Newman AM, Stehr H, Azad TD, et al.Early detection of molecular residual disease in localized lung cancer by circulating tumor DNA profiling. Cancer Discov. 2017;7:1394-1403.
- Serrano MJ, Garrido-Navas MC, Diaz Mochon JJ, Cristofanilli M, Gil-Bazo I, Pauwels P, et al. Precision prevention and cancer interception: the new challenges of liquid biopsy. Cancer Discov. 2020. [Epub ahead of print].
- Ilie et al.
- Leighl NB, Page RD, Raymond VM, et al. Clinical utility of comprehensive cell-free DNA analysis to identify genomic biomarkers in patients with newly diagnosed metastatic non-small cell lung cancer. Clin Cancer Res. 2019;25(15):4691-4700.
- About the Authors: Dr. Rolfo is director of the Thoracic Medical Oncology Department and the Early Phase Clinical Trials Section, School of Medicine, University of Maryland. Dr. Malapelle is with the Department of Public Health, University Federico II, Naples, Italy.
