A novel biomarker protein panel for lung cancer, a promising first step

Lung cancer (LC) is the most lethal cancer worldwide in both genders, tobacco consumption is causally associated with lung cancer, around 85% of all patients worldwide have tobacco consumption history (1,2). The 5-year survival of patients diagnosed at early stage and localized lung cancer is about 50%, which is considerably better compared to later stages (3). However, around 61% of patients are diagnosed in advanced stages (III and IV), when the therapeutic options are limited and the prognosis is usually poor, with a 5-year survival of only 5–15% (4,5). Even though important breakthroughs, progress in biomedicine, new diagnostic tools and the development of targeted scheme treatments, the main challenge with LC is to improve early detection of the patients, because according to different projections, the number of LC cases is expected to raise in the next years (4,6).

The annual mortality rate for lung is higher than the mortality rates from other neoplasms, such as prostate, breast, and colon cancer, it should be noted that these neoplasms already have validated tools for early detection and diagnosis in early stages (7). A risk biomarker is defined as the one that can distinguish individuals at risk but who still do not have a measurable disease. A detection biomarker for early stages of the disease ideally allows to discriminate between groups of individuals at risk of developing the disease, additionally, must be able to distinguish the populations of individuals at risk before or after the disease is measurable (8). Nevertheless, any of these kind of biomarkers have been validated for LC.

Since the last half of the last century, several studies of screening with chest X-rays and sputum cytology were evaluated, the result was the increasing number of lung cancer diagnosed without any improve of lung cancer specific mortality (8-10). High-risk profiles have been described for heavy smokers, who are defined as subjects with asbestos exposure, 30 or more pack-years of smoking history, or being older than 50 years, however, no models that use any biomolecular markers have been assessed and incorporated to clinical guidelines. Subjects at risk to develop LC, could be asymptomatic for years before being diagnosed. Therefore, the development of efficacious LC risk assessment models for use in this critical period capable to recognize high risk subjects and increase the rate of opportune detection and consequently initiate early treatment is a critical need (11).

The Early Lung Cancer Action Program started in the 1990’s utilizing chest computed tomography (CT) imaging, it was a large lung cancer screening trial with success, which showed that the use of low-dose computed tomography (LDCT) to screen current or former heavy smokers can reduce lung cancer mortality (12,13) and prompted the design of the National Lung Cancer Screening Trial (NLST), which results reported a 20% reduction in LC mortality, in high risk patients for LC after a median follow-up of 6.5-year, compared with conventional image screening (chest X-ray). Nowadays, the US preventive services task force (USPSTF) praises LDCT screening for LC among subjects with age between 55 to 80 years, with tobacco history (30 pack-years for at least 15 years), nevertheless, LDCT screening detects a considerable number of nonspecific nodules, in addition to the fact that about half of LC cases occur in subjects who are do not meet the criteria for screening (13-15).

The recent avenues in molecular biology strategies and the integration of analytical platforms, including “omics” approaches, have recognized several potential biomarkers in diverse biological samples (urine, saliva, sputum, blood, exhaled breath condensate, bronchial specimens), but none have yet received the approval to be included in the regular test panel for LC (8).

Last July, the Integrative Analysis of Lung Cancer Etiology and Risk (INTEGRAL) Consortium of Early Detection of Lung Cancer published the results of a LC risk prediction model based on a panel of selected circulating proteins combined with the traditional smoking history-based risk model. In the study, using one cohort, a blood based biomarker score was developed and compared against the traditional smoking history-based risk model alone, subsequently, it was externally validated using pre-diagnosis samples from two other independent cohorts (16). The results of this study revealed an overall specificity of 0.83, grounded on the US prevention Services Task Force screening criteria, the sensitivity of the integrated risk prediction (biomarker) model was 0.63, compared with 0.43 for the smoking model. On the other hand, furthermore, the integrated risk prediction model yield a specificity of 0.95 compared with 0.86 for the smoking model alone (1). The results of the study mark a potential improvement of the LDCT screening for the risk assessment of lung cancer, and represent a big step forward in the development and validation of a panel of biomarkers.

Four proteins were analyzed on these studies: cytokeratin-19 fragment (CYFRA 21-1), carcinoembryonic antigen (CEA), cancer antigen 125 (CA125), and the precursor form of surfactant protein B (Pro-SFTPB). CA125 is a glycoprotein produced in fetal tissue, it has been described that elevated serum CA125 levels are found in patients with seminal vesicle carcinoma, in ovarian cancer CA125 is utilized as a tumor marker for screening and management, furthermore, in LC, it has been reported the association of CA125 with bad prognosis (17). CEA is an oncofetal protein, member of the immunoglobulin family that is usually over-expressed in a number of neoplasms, including LC. Elevated serum CEA levels have been associated with advanced stages of NSCLC, brain metastases and poor prognosis (18). CYFRA 21-1, a polypeptide that recognizes soluble cytokeratin, has been reported as the most sensitive biomarker to subtyping NSCLC and differentiating LC from non-maligns conditions (19). Pro-SFTPB is a circulating protein synthesized by nonciliated bronchiolar cells and type 2 alveolar pneumocytes. Pro-SFTPB is over-expressed in LC cells, particularly in adenocarcinomas; it has been reported that pro-SFTPB is a potential independent predictor of LC (20).

The main challenge before protein biomarkers panels can be used routinely in clinical practice is the need to validate their clinical utility. Although the study performed by INTEGRAL consortium provides good results with the first validation in different cohorts, the avenues to generate robust evidence to show clinical utility are still long and complicated. A prospective clinical trial, where the primary objective is the validation and calibration of the integrated risk prediction model of the biomarker panel, should be the ideal strategy, but conduct such trials is expensive and time-consuming (21). Other options are conduct what have been called prospective retrospective clinical studies, using patient specimens that have been collected and archived from previously conducted clinical trials that have addressed the potential use of the tumor biomarker test (22,23), or, as the authors propose on this paper, the use of a larger pre-diagnostic sample size (16). Additionally, the biomarker panel path to the clinic use, is likely to be longer than the one for a single molecule, due to exacerbation of the typical difficulties related with biomarker development by merging “omics” methodologies (24). Proteomic technologies used in biomarker innovation are usually not transferable to clinical laboratories given to their high complexity, their low throughput and their analytical performance features (21), consequently, transferring the use of proteomic biomarkers from the investigative analysis phase to the clinical phase, require steady measuring platforms and prove to be economically viable (21,24).

Having pointed out the difficulties that the panel still faces in its development, is important to highlight how biofluids-based markers analysis are a rapidly expanding area of biomedicine in translational cancer research, as it could be valuable in a wide range of applications, such as opportune diagnosis, prognosis data, stratification and follow-up of patients at real time, therapeutic targets, and resistance mechanism (25). Analysis of tissue samples are critical to identify a biological link among a biomarker and cancer risk, but standard tumor biopsies are not easily to acquire, they put the patient at risk, and might not accurately reflect the molecular alterations of tumors due to either suboptimal tissue acquisition or tumor heterogeneity, furthermore, biomarkers that involve biopsy are not pragmatic for assessing cancer risk or for the follow-up of the clinical response (24). Moreover, detection strategies based on the analysis of biofluids represent an appealing strategy for screening owed to offering a non-invasive attainment that ends up allowing a large number of samples available for analysis without any substantial risk for the patients, this would impact significantly the economic cost of the disease and its impact on health systems.

As conclusion, the results presented by the INTEGRAL consortium are encouraging, and it is necessary to validate this protein panel in order to stablish it as a stable, reproducible and non-invasive measured biomarkers panel.

Acknowledgements

None.

Footnote

Conflicts of Interest: Oscar Arrieta has received honoraria as advisor, participated in speakers’ bureau and given expert opinions to Pfizer, AstraZeneca, Boehringer-Ingelheim, Roche, Lilly, and Bristol-Myers Squibb. Other authors have no conflicts of interest to declare.

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