Clinical significance of ctDNA analysis as Minimal Residual Disease Test in Lung Cancer

Unmet needs in lung cancer

While previous article is about MRD in general(click here to read previous page), this will mainly focused on MRD in lung cancer. The importance of early detection in lung cancer cannot be stressed enough. The more disease progresses, the more likely the outcomes after cancer treatment will be worse. The International Association for the Study of Lung Cancer (IASLC) has conducted projects to stratify overall survival based on the TNM stage. According to TNM stage grouping 8th edition, the overall survival of lung cancer patients show an inverse relationship with later stages.[1] The clinical stage IA1 NSCLC is associated with  a 5-year overall survival of 92% while it falls to nearly 60% in IIA.[1] However, despite this high overall survival rate in early stage patients, recurrence after chemotherapy treatment is still common. In case of patients with completely resected stage II-IIIA NSCLC, nearly a third experience recurrences.[2] Although minimal residual disease (MRD) test is more commonly used in blood cancer, MRD test holds potential to meet unmet needs in solid lung cancer.

Liquid biopsy as tool for MRD test

Since the first application of liquid biopsy by Pantel and Alix-Panabieres using circulating tumor cells (CTC), technology for liquid biopsy has evolved and showed promising results in terms of disease monitoring in solid tumors[3,4]. Other than CTC, circulating tumor DNA (ctNDA) has been investigated for its use as MRD test and showed potential as a strong prognostic indicator in terms of progression free survival and relapse.[5] The use of ctDNA has shown promising results after curative-intent-therapy and before clinical or radiographic disease recurrence.[5] Conventional imaging such as PET or CT scan hold limitations as it relies on detection of visible lesions occupying the space and cannot detect MRD.[6] In addition, there are high demands for less invasive procedures.[6] Therefore, MRD test using ctDNA in lung cancer may be an alternative option for personalized treatment and prediction of relapse. The following paragraph shows some of the studies which investigated the potential and clinical significance of MRD test after lung cancer treatment or surgery.

Clinical utility of MRD test using ctDNA in lung cancer

Chaudhuri et al. investigated the clinical significance of ctDNA as MRD test through retrospective study using blood and tissue samples obtained from lung cancer patients and healthy adults, and suggested 4 findings.[4] First, the tumor volume shows correlation with ctDNA. For patients with detectable ctDNA before getting treatment, patients with stage II-III had higher levels of ctDNA compared with stage I.[4] Second, detectable ctDNA had a significant effect on freedom from progression and survival. Patients without detectable ctDNA had significantly higher freedom from progression and survival than those present with ctDNA.[4] Third, compared with ct imaging, it detected the recurrence around 5 months earlier in over 70% of patients.[4] Lastly, to seek utility of ctDNA for MRD test, the study was further investigated using MRD landmark defined as the first blood drawn within 4 months from posttreatment. In accordance with previous data, over 90% without ctDNA MRD were free from progression at 36 months while none of the patients with detectable ctDNA MRD were free.[4]

In 2017, Abbosh et al, led the TRACERx study to investigate the use of ctDNA profiling to predict relapse of lung cancer. 

At least 2 single nucleotide variants (SNVs) were used as threshold to decide ctDNA positive.[7] From the subgroup study, ctDNA was detected in over 90% of patients (13/14) who had either prior or later experienced NSCLC relapse.[7] Such findings suggest the potential of ctDNA for residual disease identification. In 2020, Abbosh et al. published another study on the utility of ctDNA for MRD detection in early-stage NSCLC. 37 out of 45 patients had ctDNA detected prior to relapse.[8] 

In 2018, Chen led Dynamic study to investigate the use of ctDNA for surveillance in surgical lung cancer patients and suggested appropriate timing for MRD test to predict recurrence. Plasma samples were collected after surgery in 3 different time points: day1, day3, and 1 month.[9] From over 200 suspected lung cancer patients, 26 who had tumors resected were included for MRD test.[9] Patients who had detectable MRD at day 3 were more likely to predict recurrence compared with those on day 1. At day 1, the difference between patients with detectable and undetectable did not show significant difference as both showed recurrence free survival of 500 days (P=0.657).[9] But patients with detectable MRD at day 3 showed significant differences falling to 278 days compared with undetectable MRD which lasted 637 days (P=0.002).[9] Such tendencies were similar in overall survival as well. As a first prospective study to investigate the ctDNA dynamic as part of MRD test for disease surveillance, Dynamic study suggested the ideal time to use ctDNA detection as part of MRD test to predict recurrence.[9] Considering the average length of stay in hospital is 3~ 10 days for patients with resected NSCLC, it may be a good option to implement MRD test by using ctDNA in day 3 after surgery to predict recurrence and optimize personalized treatment. 

Hurdles to overcome to use MRD test through ctDNA analysis

There are several hurdles that need to be overcome to apply MRD test using ctDNA. Among those several challenges, using sensitive techniques is essential. Especially in early NSCLC and post-surgical MRD, low quantities of cfDNA in plasma may affect MRD test. Results on ctDNA mutant allele frequency (MAF) were collected to suggest current evidence on sensitivity of available technique. For detection of ctDNA, maximum and minimum median MAFs per cell-free DNA sample was 0.31% and 0.07% respectively in stage I NSCLC patients, while in stage II NSCLC patients, it was 0.48% and 0.16%.[10] Based on these data, it is suggested that to use ctDNA for screening in early stage NSCLC, MAF of <0.5% is minimally required and <0.1% to identify post-surgical MRD.[10] For late stage lung cancer, MAF may be detected over 10%.[10] Therefore, when choosing the diagnostic method, it is suggested to consider the MAF and the stage of disease the ones aim to apply MRD test. 

Conclusion 

Most of the studies up to date rely on NSG to apply MRD test using ctDNA. However, NSG has limitations as it is prone to artifactual errors which may cause false positives. Diagnostic technology with sensitivity that can reach MAF of 0.1% without causing false positives and short turnaround time may be a game changer. Genecast ADPS™ technology relies on widely used qPCR, but its unique ability can distinguish mutant genes from normal genes. Most importantly, experimental data suggested that it can be used to detect MAF from a range of as low as 0.0001% to 100%, and in a real world setting, it can reach 0.01%. Exploring the use of MRD test through ctDNA by qPCR could be an efficient and economic way to aid prediction of recurrence and personalized treatment for lung cancer patients.

Reference

[1]Goldstraw P, et al. The IASLC Lung Cancer Staging Project: Proposals for Revision of the TNM Stage Groupings in the Forthcoming (Eighth) Edition of the TNM Classification for Lung Cancer. J Thorac Oncol. 2015;11(1):39-51.    

[2]Masago K, et al.  Targeting minimal residual disease after surgery with molecular targeted therapy: the real path to a cure?. J Thorac Dis. 2018;10:S1982-S1985. 

[3]Babayan A, et al. Advances in liquid biopsy approaches for early detection and monitoring of cancer. Genome Medicine. 2018;10:21.

[4]Chaudhuri et al. Early Detection of Molecular Residual Disease in Localized Lung Cancer by Circulating Tumor DnA Profiling. Cancer Discov. 2017;7(12):1394–403.                                                                                                                           

[5]Peng Y, et al. Circulating Tumor DNA and Minimal Residual Disease (MRD) in Solid Tumors: Current Horizons and Future Perspectives. Front. Oncol. 2021;11(763790). 

[6]Wu CW, et al. Circulating Tumor Cells as a Tool of Minimal Residual Disease Can Predict Lung Cancer Recurrence: A longitudinal, Prospective Trial.

Diagnostics. 2020;10(144).

[7]Abbosh C, et al. Phylogenetic ctDNA analysis depicts early stage lung cancer evolution. Nature. 2017;545(7655):446–451.

[8]Abbosh C, et al. Abstract CT023: Phylogenetic tracking and minimal residual disease detection using ctDNA in early-stage NSCLC: A lung TRACERx study. Cancer Res. 2020;80(16_Supplement):CT023.        

[9]Chen K, et al. Perioperative Dynamic Changes in Circulating Tumor DNA in Patients with Lung Cancer (DYNAMIC). Clin Cancer Res. 2019;25:7058–67.

[10]Abbosh C, et al. Early stage NSCLC -challenges to implementing ctDNA-based screening and MRD detection. Nature Reviews Clinical Oncology. 2018;15:577–586.