Serum and blood based biomarkers for lung cancer screening: a systematic review

Lung cancer is the second most common cancer and the leading cause of cancer death for both men and women [1‐3]. In 2015, an estimated 26,600 Canadians were diagnosed with, and 20,900 died from, lung cancer [2]. In 2014, 163,422 patients from the UK died from lung cancer, with lung cancer projected to continue as the leading cause of cancer-related death until 2035 [3]. The five year survival rate for patients diagnosed with late stage lung cancer and metastatic lung cancer are 16.8% and < 5% respectively [1]. Conversely, the 5-year survival rate of small intrapulmonary cancers is 80% [4]. Therefore, identification of lung cancer at an early stage could potentially lead to significant decreases in morbidity and mortality [5, 6].

In 2010, the National Lung Screening Trial (NLST) demonstrated a 20% reduction in lung cancer mortality and 7% reduction in all-cause mortality by screening patients at high risk of lung cancer with low-dose chest CT (LDCT) scans (NNS = 320) [1, 4]. However, 24.2% of patients who had LDCT exhibited abnormal findings, and 96.4% of these findings were false positive results, representing a 18% over-diagnosis rate [1, 4, 7]. The high rate of false positives has led to multiple screening rounds with high radiation exposure, a high use of harmful diagnostic follow-up, increased patient costs and anxiety [4, 8]. Therefore, while LDCT may be effective in reducing lung cancer mortality, there is a need to improve the accuracy of lung cancer screening to decrease morbidity and health-care associated costs.

Molecular biomarkers are potentially useful adjuncts to LDCT for lung cancer screening, either by further delineating patient risk prior to LDCT, or assessing malignant risk of positive LDCT findings [1, 4, 6, 9, 10]. The performance of any test also depends upon the prior probability of the condition in the population being sampled and this varies considerably [11, 12]. Biomarkers may be generated from cancer cells, the tumor microenvironment, or the host response to cancer [4, 13]. Various molecular factors that are implicated in lung carcinogenesis have been evaluated as prognostic and diagnostic biomarkers, such as markers of apoptosis, cellular adhesion, cellular growth, and tumor proliferation [10, 14]. Epigenetic markers such as DNA methylation, miRNAs, nucleosome remodeling, and histone modifications have also been investigated [10, 13, 14]. Biomarkers may be sampled from many different bodily sources, including whole blood, serum, plasma, bronchial brushings, and sputum [13, 14]. Circulating blood-based and serum-based biomarkers are a convenient compartment to sample as they are relatively easy and inexpensive to collect [4, 6, 9].

The EarlyCDT-Lung test is a commercially available blood test based on ELISA principles that measures a panel of seven tumor-associated autoantibodies: p53, NY-ESO-1, CAGE, GBU4–5, SOX2, HuD, and MAGE A4 [15]. The miR-test is a serum based miRNA test that measures a signature of 13 miRNAs: miR-92a-3p, miR-30b-5p, miR-191-5p, miR-484, miR-328-3p,miR-30c-5p, miR-374a-5p, let-7d-5p, miR-331-3p, miR-29a-3p, miR-148a-3p, miR-223-3p, miR-140-5p [16]. The MSC is a plasma-based miRNA test that categorizes patients into low, intermediate, or high risk of disease based on pre-defined positivity for 24 miRNA expression ratios [17]. Of the available blood and serum-based biomarkers, only EarlyCDT-Lung, Serum-based miRNA signature (miR-test), and Plasma-based miRNA test (MSC) have entered Phase 4 of development [4]. There is, therefore, a need to evaluate the current state of biomarker development, especially EarlyCDT-Lung and miRNA based strategies, to guide future research in lung-cancer screening.

This literature review describes the diagnostic performance of EarlyCDT-Lung, miR-test, and MSC as adjunctive biomarkers to LDCT for the diagnosis of lung cancer. The key questions considered for this review are:

EarlyCDT-lung, miR-test, and MSC were chosen as the focus for this review as they are reported as the biomarkers at the most advanced phase of development for the detection of lung cancer [4]. This review focuses on clinically relevant measures for lung cancer screening, including measures of diagnostic performance and impact on lung cancer-related mortality and all-cause mortality.

All three biomarkers show promise in their diagnostic ability to detect lung cancer. The plasma-based micro-RNA signature classifier (MSC) trended towards the highest sensitivity, specificity, and positive likelihood ratio for the detection of lung cancer. However, a direct comparison between the three biomarker signatures cannot be made at this time as sample sizes are small, confidence intervals for performance measures are wide, no trials have directly compared the three biomarker signatures, and the number of trials evaluating each biomarker is singular.

The only trial that directly evaluated the diagnostic ability of a blood-based biomarker in conjunction with LDCT shows promise that biomarkers can be useful adjuncts to LDCT in screening for lung cancer. When using MSC in conjunction with LDCT, a positive likelihood ratio of 18.6 was achieved if both MSC and LDCT were positive, while a negative likelihood ratio of 0.03 was achieved if both MSC and LDCT were negative. This suggests that biomarker signatures may potentially be a means to risk stratify at-risk patients for the development of lung cancer.

Although blood-based biomarkers show promise, there currently is no high quality prospective literature to guide the implementation of blood-based biomarkers in clinical practice for lung cancer detection. Prospective phase 4 studies are currently ongoing to assess the value of the above biomarkers for their value as a pre-CT screening tool. The Early Lung Cancer Detection Study (ECLS) is currently ongoing in Scotland, randomizing approximately 12,000 people from the Greater Glasgow and Clyde area to the EarlyCDT-lung test or routine care (ClinicalTrials.​gov ID: NCT01925625) [22]. Patients with a positive Early-CDT-lung test undergo a CT scan at baseline followed by CT scans every 6 months for 24 months. The primary outcome is the difference at 24 months in the number of patients with late stage lung cancer (Stages 3 and 4). The COSMOS II study enrolling approximately 10,000 high risk subjects in Italy will evaluate prospectively miR-Test in conjunction with LDCT [16]. Similarly, the Plasma microRNA Profiling as First Line Screening Test for Lung Cancer Detection (BIOMILD) trial will enroll approximately 4000 subjects to evaluate the MSC as a potential first line screening test for lung cancer (ClinicalTrials.​gov ID: NCT02247453) [23].

Limitations of this work include the small number of studies identified and the substantial variability across studies in terms of inclusion criteria, methodology, follow-up, timing, and comparators. The number of patients enrolled was small and follow up period for each study was relatively short. It is important to note that the inclusion criteria for these studies varied regarding pack-years of smoking and how patients were enrolled from their larger parent trials. These trials were conducted in different countries where attitudes, laws, and public health policies regarding smoking differed. As our search focused on the three biomarker signatures (EarlyCDT-Lung, miR-test, and MSC), studies regarding other biomarker signatures would not have been included. Finally, studies published in languages apart from English would not have been included.

Although blood and serum-based biomarkers are promising adjuncts to LDCT for the detection lung cancer, there is currently no high quality evidence to support or guide the implementation of these biomarkers in clinical practice. Prospective studies are ongoing to evaluate the diagnostic performance and impact of biomarkers on clinically relevant outcomes. Further research is required to guide clinical implementation.