The impact of alpha-1 antitrypsin deficiency alleles on lung cancer survival

Introduction

Lung cancer (LC) is considered to be one of the leading causes of cancer-related mortality in many regions around the world (1). Beyond the tumour, node and metastasis (TNM) staging system (2), few prognostic factors have been identified to allow us to predict patients’ future evolution in our routine clinical practice.

Alpha-1 antitrypsin (AAT) is a water-soluble glycoprotein primarily synthesized in the hepatocytes (80%) (3). Pi*M (Pi: protease inhibitor) is the most common allele and is present in over 90% of normal subjects, with the most common deficiency alleles being Pi*S and Pi*Z (4).

Different studies have shown that carrying an AAT deficiency allele is an independent risk factor for developing LC (5-9). However, to date, little is known regarding whether carrying a deficiency allele may be a prognostic factor in the evolution of LC. We present this article in accordance with the REMARK reporting checklist (available at https://tcr.amegroups.com/article/view/10.21037/tcr-23-743/rc).

Methods

A prospective observational study was carried out which consecutively included patients diagnosed with LC in University Hospital “Nuestra Señora de Candelaria” between December 2017 and August 2020.

The study was conducted in accordance with the Declaration of Helsinki (as revised in 2013). The study was approved by the Ethics Committee of the University Hospital “Nuestra Señora de Candelaria” (Code PI 75-17), and informed consent was taken from all the patients. The inclusion criteria were: >18 years old with an LC diagnosis confirmed with histological study. The existence of a concomitant infection at the time of diagnosis, starting active oncological treatment before the blood extraction (determining AAT protein serum levels/AAT genotype) and/or the patient declining to participate in the study were reasons for exclusion. Patients’ age, tobacco history, body mass index, AAT serum levels at the time of diagnosis, AAT genotype, histological LC type and comorbidities (arterial hypertension, dyslipidemia, diabetes mellitus, heart failure, atrial fibrillation, ischemic heart disease, stroke and chronic kidney disease) were recorded. LC extension was determined using the 8th edition TNM staging system (2), and the age adjusted Charlson comorbidity index (CCI) was calculated.

A blood sample was taken from each of the patients in order to determine both AAT serum concentration and genotype. AAT serum values were determined using nephelometry (BN ProSpec System, Siemens, Berlin, Germany). Genomic DNA was purified from EDTA whole blood (MagCore^® Genomic DNA Whole Blood Kit, RBC Bioscience, Buenos Aires, Argentina). The two most common deficiency alleles (PI*S and PI*Z) were genotyped using real-time polymerase chain reaction (PCR) with TaqMan probes (Applied Biosystems 7500, Thermo Fisher Scientific, Waltham, USA). The genotypes obtained were correlated with the reference AAT plasma values at University Hospital “Nuestra Señora de Candelaria”. Patients with AAT serum levels that did not match those expected for the S/Z genotypes obtained underwent complete sequencing of the coding exons and flanking intronic regions of the SERPINA1 gene using an AB3500 capillary sequencing instrument (Applied Biosystems), comparing the results obtained with the reference sequence NM_001127701.1 (SeqScape 3.0, Thermo Fisher Scientific). Based on AAT genotype, patients were divided into the deficiency (Pi*≠MM) or non-deficiency (Pi*=MM) group.

Student’s t-test was used for continuous variables and the Chi-square test and Fisher’s exact test were used for categorical variables. The survival curves were generated using the Kaplan-Meier method and compared using the log-rank test. Univariate and multivariate survival analyses were carried out using the Cox proportional hazards regression model and confidence intervals of 95% were estimated for the hazard ratio (HR). The assumed constant HR was verified (χ²=0.43; P=0.511). This statistical analysis used IBM SPSS (Statistical Package for the Social Sciences) version 22.0 (IBM Corp., Armonk, NY, USA). P values ≤0.05 (bilateral) were considered significant.

Results

Of the 167 patients initially included, the analysis was carried out in 164 (3 patients were lost to follow-up). They were primarily male (63.4%), with an average age of 64.5±9.1 years and 52.4% were current smokers; the average CCI score was 8±2. The average length of follow-up was 13±10 months. Ninety-two patients (56.1%) passed away, with an average follow-up of 9±7 months. The most frequent histological type of LC was adenocarcinoma (40.9%). Patients were classified as stage I (4.2%), stage II (8.3%), stage III (31.2%) and stage IV (56.3%), according to TNM staging.

Twenty-eight patients (17%) were carriers of a deficiency allele (26 Pi*MS, 1 Pi*MZ, 1 Pi*MM_heerlen). No significant differences were found with respect to baseline characteristics between Pi*≠MM and Pi*=MM, including AAT serum levels (Tables 1,2). Patients in the Pi*≠MM group had a higher risk of death in the first 6 months after the LC diagnosis compared to Pi*=MM subjects (HR =2.04; 95% CI: 1.04–4.0; P=0.038) (Figure 1A). A second analysis was performed excluding small cell LC, maintaining an increase in mortality in the first 6 months in those subjects carrying deficient alleles (HR =2.24; 95% CI: 1.11–4.55; P=0.025) (Figure 1B). This difference is diluted if we consider the entire follow-up of the patients (HR =1.44; 95% CI 0.87–2.40; P=0.156 and HR =1.48; 95% CI: 0.88–2.51; P=0.142, respectively), this may be motivated because the group of patients with a genotype from 6 months of follow-up is small in size sample (Figure 1). The treatments (surgical or pharmacological) used in both groups according to staging were evaluated, however, no differences were observed in terms of treatment.

Figure 1 Survival of patients with lung cancer based on the presence of an alpha-1 antitrypsin deficient allele. (A) Kaplan-Mayer curve of cumulative survival between patients with lung cancer with and without altered genotype throughout the follow-up. (B) Kaplan-Mayer curve of cumulative survival between patients with lung cancer with and without altered genotype throughout the follow-up excluding patients with small cell lung tumor. *, P<0.05. Pi*=MM, alpha-1 antitrypsin non-deficiency genotype; Pi*≠MM, alpha-1 antitrypsin deficiency genotype.

Discussion

Different studies have shown that those subjects who are carriers of deficiency alleles, regardless of their degree of tobacco consumption, have a greater risk of developing LC (9,10). With a described prevalence of around 13% (8,9), these figures are slightly lower than those detected in our study, which could be justified by the high prevalence of deficiency alleles in our setting (11). In light of these findings, some authors postulate the theory that in subjects with deficiency alleles, there is a clear protease-antiprotease imbalance originating from low AAT concentrations in the blood and tissues, which would predispose them to a tissue environment that favors carcinogenic action and consequently the development of LC. Other hypotheses postulate that the presence of low AAT levels can promote neoplasm progression by inhibiting the apoptotic capacity of tumor cells that, along with neutrophil elastase, can activate matrix metalloproteinases, a group of enzymes that play a fundamental role in tumor invasion and the origin of metastases (12,13).

Studies analyzing whether the presence of a deficiency genotype can have any sort of impact on LC prognosis are scarce. Li et al. (14) did not find any difference in survival according to carrier status in patients diagnosed with non-small cell LC. However, in our study, those patients with LC (small cell and non-small cell LC) who carried a deficiency allele did show worse survival at 6 months after diagnosis, results that is maintained even after excluding those patients with small cell LC. Compared to the patients included in the study by Li et al., the majority of the subjects in our sample are in advanced stages of the disease and are not suitable for curative surgery, which will influence their prognosis. Given the fact that our sample primarily focuses on stages III and IV, our results provide clinical value in these patients for whom there is not a curative option.

It is important to note that in our sample, there were no significant differences between AAT serum levels in patients carrying a deficiency allele compared to non-deficiency patients. This leads us to believe that the problem may stem from AAT activity. Its dysfunction would cause an imbalance between protease-antiprotease, not in quantity but rather functionality, where despite normal or even elevated AAT levels, said protein has little or no anti-elastase activity (4,15,16).

The main limitations of this study are its small sample size, the limited number of patients in early stages of the disease and the absence of subjects with the severe deficiency genotype, but the results provide a starting point for future lines of research.

Conclusions

Based on all of this, the presence of an AAT deficiency genotype could be a potential prognostic marker in advanced LC. However, larger studies that justify these findings are needed.

Acknowledgments

Funding: This study was supported by a grant from the Asociación Canaria de Neumología y Cirugía Torácica (NEUMOCAN).

Footnote

Reporting Checklist: The authors have completed the REMARK reporting checklist. Available at https://tcr.amegroups.com/article/view/10.21037/tcr-23-743/rc

Peer Review File: Available at https://tcr.amegroups.com/article/view/10.21037/tcr-23-743/prf

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://tcr.amegroups.com/article/view/10.21037/tcr-23-743/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki (as revised in 2013). The study was approved by the Ethics Committee of the University Hospital Nuestra Señora de Candelaria (Code PI 75-17), and informed consent was taken from all the patients.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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