|Year : 2019 | Volume
| Issue : 2 | Page : 221-223
Liquid biopsy in lung cancer-hope or hype?
Anuradha Choughule, Hollis D'Souza
Department of Medical Oncology, Tata Memorial Hospital; Homi Bhabha National Institute (HBNI), Mumbai, Maharashtra, India
|Date of Web Publication||20-Dec-2019|
Department of Medical Oncology, Molecular Laboratory, Tata Memorial Hospital, Mumbai, Maharashtra; Homi Bhabha National Institute (HBNI), Mumbai, Maharashtra
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Choughule A, D'Souza H. Liquid biopsy in lung cancer-hope or hype?. Cancer Res Stat Treat 2019;2:221-3
Lung cancer is the leading cause of cancer incidence and mortality, with 2.1 million new lung cancer cases and 1.8 million deaths predicted in 2018, representing around 1 in 5 (18.4%) cancer deaths. According to the GLOBOCAN 2018 report, the estimated incidence of lung cancer in India was 67,795 in all ages and both sexes. In both sexes combined, lung cancer is the most commonly diagnosed cancer (11.6% of the total cases) and the leading cause of cancer death (18.4% of the total cancer deaths). The major risk factor for developing lung cancer is tobacco use, and this disease is often viewed solely as a smoker's disease. However, a significant number of patients with lung cancer have no history of smoking. In a study on epidemiological patterns and clinical profile of 489 lung cancer patients in India, it was found that 255 (52%) were non-smokers and 234 (48%) were smokers, thereby concluding higher numbers of Indian patients with lung cancer are non-smokers, compared to the West, where 80% of lung cancers can be attributed to smoking.
Over the past decade, the treatment of non-small cell lung cancer (NSCLC) has evolved. There has been a significant improvement in the management of advanced stages primarily due to an increased understanding of the molecular heterogeneity and drivers of lung cancer initiation and progression. Mutations within the epidermal growth factor receptor (EGFR), anaplastic lymphoma kinase, fibroblast growth factor receptor, ROS1, KRAS, HER2, BRAF, MET, and RET were discovered. Mutations in EGFR, first discovered in 2004, are present in up to 10%–15% of all patients with NSCLC. Mutations are predominantly located in EGFR exons 18–21. 85% of the mutations are either deletions in exon 19 or a single-point substitution mutation in exon 21 (L858R). Studies have shown the most common demographics as never smokers, female gender, and Asian ethnicity.
In NSCLC, the analysis of EGFR mutation is a prerequisite for determining the appropriate tyrosine kinase inhibitor to be used in targeted treatment to improve patient outcomes and survival. Tissue biopsy is still regarded as the 'standard procedure' for molecular detection and was indispensable in decision-making to decide treatment for advanced NSCLC patients before 2016. The appropriate methods to detect EGFR mutations are Sanger, pyrosequencing and next-generation sequencing (platform dependent). Tumor tissue is often not available due to the invasiveness of the tumor; in patients with poor performance status, significant respiratory distress, and who are frail and older, it is difficult to obtain the specimen. Especially for those targeted therapy-resistant patients, re-biopsy is extremely difficult due to the suboptimal clinical condition.
The current approaches in molecular targeted therapies in NSCLC and advancements in mutation detection technologies have become a valuable addition to address the treatment planning for the increasing burden of lung cancer, and circulating tumor DNA (ctDNA) or liquid biopsy, in recent years, has been at the forefront of research and transition to a clinical setting. Historically, tissue biopsy is the gold standard for establishing the EGFR mutation status. In recent years, liquid biopsy (cfctDNA) from body fluids other than plasma, such as ascitic fluid, cerebrospinal fluid, and pericardial effusion has also gained importance as a potential alternative source of tumor genetic material for molecular diagnostics. The hypothesis of liquid biopsy, cell-free ctDNA, has been documented as a promising alternative to tissue biopsy for EGFR testing, and well established from the encouraging results of clinical outcomes in one of the most recent global clinical trials on NSCLC patients. To date, to the best of our knowledge, in an Indian population, the current study on 163 NSCLC patients provides the largest cohort of data demonstrating the application of liquid biopsy/ctDNA-based EGFR mutation detection in blood. The detection of plasma EGFR mutations in NSCLC patients with a validated droplet digital polymerase chain reaction (ddPCR) lung cfDNA assay is a highly specific and sensitive technology; although, it is not an FDA approved technology. However, the value of cfDNA assays in cancer management still remains controversial.
In the study published in this issue of the journal, Pandey et al. demonstrated the clinical utility of liquid biopsy in NSCLC. It is a retrospective study conducted between 2017 and 2019 in 28 patients who could not have a tissue diagnosis for EGFR testing. The authors divided the reasons for not having a tissue diagnosis into patient refusal, poor performance status, inadequate tissue or only cytological samples. Of these, 11 (39%) were EGFR mutation-positive, while the remaining 17 (61%) were negative. Of the 11 patients, 4 had exon 19 deletion, 6 had exon 21 deletion, and 1 had exon 20 T790M mutation. The TKI offered was physician choice for the exon 19 and exon 21 deletion patients, and osimertinib was given to T790M-mutated patients. The EGFR-negative patients were offered physician choice chemotherapy. In the EGFR positive and EGFR-negative cohorts, the response rates were 63% and 12%, respectively. The median follow-up was 14 months (range 10–17 months). The median PFS was 8 months versus 2 months (P = 0.002) and the median OS was 17 months versus 5 months (P = 0.004), in the EGFR-mutated versus the EGFR wild-type patients.
This novel study has followed up patients who are treated with TKI on the basis of liquid biopsy alone. The response rates and PFS are comparable with other studies utilizing tissue biopsy.,, This cohort had >50% of patients with a performance status >2, which is a real-world figure in our country. Although the study was only performed in non-smokers and with a small patient population and it is a retrospective study, the results are comparable with other studies in the literature. The use of osimertinib as per the FLAURA trial is not feasible in an economically backward population, hence it cannot be applied in the situation. In addition, the study has not provided a concordance with tissue biopsy, which limits its validity.
As regards the performance of the molecular tests for liquid biopsy, as in this article, strict adherence to technical details is needed. Whole blood has to be centrifuged at 1600G for 10 min at 4°C, then the supernatant to be centrifuged at 16000G for 10 min at 4°C. Plasma has then to be stored at –80° until further assay. ctDNA can also be processed in other body fluids such as ascitic fluid, pericardial effusions, and pleural effusions. The study authors have limited themselves to blood specimen only. ddPCR-based diagnostic test is available for detecting 45 mutation sites within the exon 18–21 region of the EGFR gene. The study limited itself to exon 19 deletion, L858R, and T790M mutations. In addition, exon 18 and exon 20 regions should also be looked for ASV ins/del; and S768I.
Commonly KIT-based assays are used for ddPCR testing; the laboratory should mention the limit of the detection of the analytical performance of the ddPCR Lung cfDNA assay by determining the Limit of Blank for single variants, and defining the detection limit, analytical specificity, and linearity of assay.
In conclusion, the treatment of NSCLC needs a molecular profile of the tumor and with EGFR mutation being the most common targetable mutation, need for alternate methods of molecular testing is the need of the hour. Liquid biopsy and its advancement will definitely be the answer in future.
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