Abstract
The aim of this study was to retrospectively analyze 18F-FDG positron emission tomography/computed tomography (18F-FDG PET/CT) metabolic variables, programmed death-ligand 1 (PD-L1) and phosphorylated signal transducer and activator of transcription 3 (p-STAT3) tumor expression, and other factors as predictors of disease-free survival (DFS) in patients with lung adenocarcinoma (LUAD) (stage IA–IIIA) who underwent surgical resection. We still lack predictor of immune checkpoint (programmed cell death-1 [PD-1]/PD-L1) inhibitors. Herein, we investigated the correlation between metabolic parameters from 18F-FDG PET/CT and PD-L1 expression in patients with surgically resected LUAD.
Seventy-four patients who underwent 18F-FDG PET/CT prior to treatment were consecutively enrolled. The main 18F-FDG PET/CT-derived variables were primary tumor maximum standardized uptake value (SUVmax), metabolic tumor volume (MTV), and total lesion glycolysis (TLG). Surgical tumor specimens were analyzed for PD-L1 and p-STAT3 expression using immunohistochemistry. Correlations between immunohistochemistry results and 18F-FDG PET/CT-derived variables were compared. Associations of PD-L1 and p-STAT3 tumor expression, 18F-FDG PET/CT-derived variables, and other factors with DFS in resected LUAD were evaluated.
All tumors were FDG-avid. The cutoff values of low and high SUVmax, MTV, and TLG were 12.60, 14.87, and 90.85, respectively. The results indicated that TNM stage, PD-L1 positivity, and high 18F-FDG PET/CT metabolic volume parameters (TLG ≥90.85 or MTV ≥14.87) were independent predictors of worse DFS in resected LUAD. No 18F-FDG metabolic parameters associated with PD-L1 expression were observed (chi-square test), but we found that patients with positive PD-L1 expression have significantly higher SUVmax (P = .01), MTV (P = .00), and TLG (P = .00) than patients with negative PD-L1 expression.
18F-FDG PET/CT metabolic volume parameters (TLG ≥90.85 or MTV ≥14.87) were more helpful in prognostication than the conventional parameter (SUVmax), PD-L1 expression was an independent predictor of DFS in patients with resected LUAD. Metabolic parameters on 18F-FDG PET/CT have a potential role for 18F-FDG PET/CT in selecting candidate LUAD for treatment with checkpoint inhibitors.
Keywords: FDG, lung adenocarcinoma, PET/CT, prognosis, programmed cell death-ligand 1
1. Introduction
Lung cancer, as a prominent global health burden is the leading cause of malignancy and disease-related mortality worldwide. Lung adenocarcinoma (LUAD) is the most prevalent histological form of non-small-cell lung cancer (NSCLC), accounting for almost half of all lung cancer cases.[1]
Despite striking advances in treatment options, including surgical resection, chemotherapy, radiation, and targeted therapies, the prognosis of LUAD remains poor.[2] Thus, it is of great importance to identify novel prognostic methods to increase the predictability of outcomes in patients with LUAD. Positron emission tomography/computed tomography (PET/CT), with its advantages of non-invasive evaluation and accuracy, has been validated in the assessment of staging, recurrence, response, and prognosis in NSCLC.[3,4]
Previous studies have demonstrated that the tumor metabolism activity of fluoro-2-deoxy-D-glucose (FDG) uptake (the maximum standardized uptake value [SUVmax]) is a significant prognostic factor in NSCLC.[5,6] However, there are some variability and discrepancies in the measurement of SUVmax.[7] Recent reports have shown a superior correlation between primary tumor total lesion glycolysis (TLG) denoting the FDG uptake of the entire lesion correlates with progress free furvival (PFS) in NSCLC patients compared with conventional SUVmax.[8] Further studies are required to verify whether the tumor volume metabolism (TLG) parameter is a better prognostic predictive factor in patients with surgically resected LUAD than conventional SUVmax.
The relationship between 18F-FDG uptake and the programmed cell death-1 (PD-1)/programmed death-ligand 1 (PD-L1) immune checkpoint is not well understood. The PD-1/PD-L1 immune checkpoint is a crucial mechanism underlying the immune escape of tumor cells from T cells.[9] The biological characteristics of patients with positive PD-L1 expression are dissimilar to those with negative expression; this results in the adoption of diverse treatment strategies and varying clinical outcomes in surgically resected LUAD patients. Several studies have shown concordance or discordance in the prognostic value of PD-L1 in surgically resected LUADs. Herein, further investigation is needed to confirm the prognostic value of PD-L1. PD-L1 expression assessed by immunohistochemistry (IHC) has been confirmed to be predictive of response to immune checkpoint inhibitors,[10] but the procedure requires an invasive biopsy. Alternative non-invasive strategies such as PET/CT that can predict PD-1/PD-L1 expression and inform treatment strategies involving anti-PD-1/PD-L1 antibodies in patients with LUAD would be of great value and could aid in seeking potential predictors of immunotherapy response.
Signal transducer and activator of transcription (STAT) 3 is activated by phosphorylation (p-STAT3) and plays an important role in regulating tumor invasion and metastasis.[11,12] However, the prognostic value of p-STAT3 expression in surgically resected LUAD is yet to be fully elucidated.
Thus, it is essential to investigate the prognostic value of PD-L1 and p-STAT3 expression and to develop a new non-invasive and practical method (PET/CT) for predicting outcomes in patients with surgically resected LUAD. We also investigated whether non-invasive strategies such as metabolic variables derived from PET/CT as predictors of immune checkpoint (PD-1/PD-L1) inhibitors.
2. Materials and methods
2.1. Patient characteristics
The Harbin Medical University Institutional Human Ethics Review Board approved this retrospective study (No. HMUIRB20160008), and the requirement for informed consent was waived. A total of 74 consecutive patients with LUAD were enrolled at the Affiliated Tumor Hospital of Harbin Medical University. All participants underwent 18F-FDG PET/CT before radical surgical resection of lung cancer between August 2010 and September 2012. The inclusion criteria were as follows: 18F-FDG PET/CT examination was performed within 4 weeks before surgery. Chest wall infiltration was not observed. The tumor had no sub-solid components. The tumor size (long diameter) was greater than 10 mm. Tumors on 18F-FDG PET/CT showed an abnormal uptake of radioactivity. All patients who underwent curative resection were diagnosed with LUAD after surgery, and the pathological reports were confirmed by more than 2 experienced pathologists. All patients were treated according to National Comprehensive Cancer Network guidelines.
Pathological staging was determined according to the Tumor-Node-Metastasis (TNM) staging diagnosis of UICC/AJCC (7th edition). The survival time after surgery was greater than 90 days. Patients who received radiotherapy, chemotherapy, or chemoradiotherapy before surgery were excluded.
2.2. Survival data
Survival data were obtained from medical records or telephone follow-ups. The follow-up period was 3 to 75 months, and 74 patients were followed up until death or until the cutoff date of November 25, 2016. Five-year disease-free survival (DFS) rate was selected as the study endpoint. DFS was defined as the time from the date of surgery to the first recurrence, metastasis, death, or cutoff date.
2.3. 18F-FDG PET/CT acquisition
All patients fasted for 4 to 6 hours. Blood glucose levels <150 mg/dL were considered normal before the 18F-FDG PET/CT examination (Discovery ST, GE Medical Systems, Milwaukee, WI). PET/CT images were obtained 60 minutes after intravenous administration of 18F-FDG (5.55–7.40 MBq/kg). The PET/CT protocol mentioned in this study was described in our previous study.[13] In this study, the output results, including the SUVmax, metabolic tumor volume (MTV), TLG of lesions were evaluated by 2 imaging and nuclear medicine physicians who had more than 3 years of working experience with 18F-FDG PET/CT imaging. Any disagreements between physicians were resolved by discussion, and consensus was achieved. The volume boundaries were automatically drawn to incorporate each tumoral lesion in 18F-FDG PET/CT images using the software (PET-VCAR, GE Healthcare, Waukeha, WI, USA) using a 40% threshold of SUVmax. Manual adjustment of the SUVmax threshold was required when the defined tumor margin was not appropriate, relative to fused CT. TLG is the MTV multiplied by the mean SUV of the tumor.
2.4. Immunohistochemistry
IHC was performed using the standard indirect immunoperoxidase procedures. Briefly, 4 μm-thick sections from a paraffin-embedded tissue block were processed. The slides were stained with primary antibodies against PD-L1 (Abcam, Cambridge, UK) and p-STAT3 (Abcam, Cambridge, UK). The IHC assay results were independently interpreted by 2 experienced pathologists, and any discrepancies were resolved by consensus. PD-L1/p-STAT3 positivity was defined per specimen by a 5% expression threshold (positive tumor cells/total tumor cells) in cases where more than 5% were considered PD-L1/p-STAT3-positive.
2.5. Statistical analysis
The association between 2 continuous variables was analyzed by t test. The association between 2 categorical variables was evaluated by chi-square test. The measurement parameters of 18F-FDG PET/CT were recorded as continuous variables. The cutoff values for the categorization of low and high SUVmax, TLG, and MTV were performed using R (version 3.3.2) with the package of survival receiver operating characteristic curve (ROC, version 1.0.3) (R Development Core Team, Vienna, Austria, http://www.R-project.org). The cutoff values for the categorization of low and high SUVmax, TLG, and MTV were calculated using the ROC curve. The cutoff value for each parameter was calculated by maximizing the Youden index. Univariate analysis of DFS was performed, and all variables with univariate significance (P < .05) were selected for a multivariable Cox model. Spearman rank correlation coefficient was used to determine the multicollinearity between parameters. SPSS19.0 (SPSS Inc., Chicago, IL) was performed using a two-tailed P value <.05, to indicate statistical significance.
3. Results
3.1. Patient characteristics
Seventy-four patients with LUAD were enrolled in the study, consisting of 38 men and 36 women with a median age of 57 (range, 38–83) years. Eleven patients were diagnosed with stage IA, 14 with stage IB, 17 with stage IIA, 4 cases with stage IIB, and 28 with stage IIIA. Based on the time-dependent ROC analysis results, the cutoff points for the categorization of low and high SUVmax, MTV, and TLG were 12.60, 14.87, and 90.58, respectively (Fig. 1). The main clinicopathological data of all patients are shown in Table 1. Selected 18F-FDG PET/CT imaging cases of surgically resected LUAD are shown in Figures 2 and 3.
Figure 1.
ROC curve for the determination of the most discriminative cutoff point for SUVmax, metabolic tumor volume-MTV, and total lesion glycolysis-TLG in primary tumors. The optimal cutoff values for SUVmax, MTV, and TLG were 12.60, 14.87, and 90.58, respectively. SUVmax = maximum standardized uptake value.
Table 1.
Correlation between PD-L1/p-STAT3 expression and clinicopathological parameters in patients with surgically resected lung adenocarcinoma.
| Characteristics | n (%) | PD-L1 expression | p-STAT3 expression | ||||
| − | + | P | − | + | P | ||
| Age | |||||||
| <60 | 45 (60.8) | 16 | 29 | .632 | 30 | 15 | .445 |
| ≥60 | 29 (39.2) | 12 | 17 | 22 | 7 | ||
| Gender | |||||||
| Male | 38 (51.35)1 | 10 | 28 | .055 | 26 | 12 | .802 |
| Female | 36 (48.65)0 | 18 | 18 | 26 | 10 | ||
| Smoking status | |||||||
| + | 28 (37.8) | 12 | 16 | .622 | 22 | 6 | .297 |
| − | 46 (62.2) | 16 | 30 | 30 | 16 | ||
| SUVmax | |||||||
| <12.60 | 55 (74.3) | 20 | 35 | .785 | 39 | 16 | 1.000 |
| ≥12.60 | 19 (25.7) | 8 | 11 | 13 | 6 | ||
| MTV | |||||||
| <14.87 | 54 (73) | 21 | 33 | .795 | 40 | 14 | .263 |
| ≥14.87 | 20 (27) | 7 | 12 | 12 | 8 | ||
| TLG | |||||||
| <90.58 | 49 (66.2) | 21 | 28 | .311 | 36 | 13 | .430 |
| ≥90.58 | 25 (33.8) | 7 | 18 | 16 | 9 | ||
| LDH | |||||||
| <190 | 60 (81.1) | 21 | 39 | .364 | 40 | 20 | .207 |
| ≥190 | 14 (18.9) | 7 | 7 | 12 | 2 | ||
| CEA | |||||||
| <5 | 43 (58.1) | 18 | 25 | .471 | 30 | 13 | 1.000 |
| ≥5 | 31 (41.9) | 10 | 21 | 22 | 9 | ||
| Stage | |||||||
| I | 25 (33.8) | 14 | 11 | .026∗ | 19 | 6 | .592 |
| II, IIIA | 49 (66.2) | 14 | 35 | 33 | 16 | ||
CEA = carcinoembryonic antigen, LDH = lactic dehydrogenase, MTV = metabolic tumor volume, PD-L1 = programmed death-ligand 1, p-STAT3 = phosphorylated signal transducer and activator of transcription 3, SUVmax = maximum standardized uptake values, TLG = total lesion glycolysis.
P < .05 considered statistically significant.
Figure 2.
A typical case of PET/CT volumetric metabolic parameters. The patient was a 55-year-old male with stage IIA moderately differentiated adenocarcinoma. PET/CT metabolic parameters were: SUVmax, 13.45; metabolic tumor volume (MTV), 5.61; and total lesion glycolysis (TLG), 34.68. Disease-free survival (DFS) was 50.5 months. PET/CT = positron emission tomography/computed tomography, SUVmax = maximum standardized uptake value.
Figure 3.
A typical case of PET/CT volumetric metabolic parameters. A 61-year-old male with stage IIA poorly differentiated adenocarcinoma. PET/CT metabolic parameters were: SUVmax, 14.26; metabolic tumor volume (MTV), 36.90; and total lesion glycolysis (TLG), 319.23. DFS was 20.8 months. DFS = disease-free survival, PET/CT = positron emission tomography/computed tomography, SUVmax = maximum standardized uptake value.
3.2. Follow-up data
The follow-up endpoint of the entire cohort was November 25, 2016 and there were 67 cases of local recurrence or distant metastasis. The tumor-free survival rates at 1, 2, 3, 4, and 5 years were 83.78%, 48.69%, 25.67%, 18.91%, and 13.51%, respectively, and the total median DFS was 23.60 months (range, 3–75 months). The median DFS in stage I patients was 37.00 months, while that in patients with stage II and IIIA was 18.70 months.
3.3. IHC results
IHC was used to detect PD-L1 expression in LUAD tissues and its relationship with clinicopathological parameters. Positive PD-L1 expression was observed in 62.2% of LUAD specimens, and PD-L1 was positively expressed in LUAD specimens (Fig. 4-A). The correlations between PD-L1 expression and various 18F-FDG PET/CT parameters are shown in Table 1. The positive expression of PD-L1 in stage II–IIIA disease was higher than that in stage I, and the difference between the 2 groups was significant (chi-squared test, P = .026), and there was no significant correlation between PD-L1 positivity and 18F-FDG PET/CT parameters. p-STAT3 was positively but weakly expressed in 29.7% of LUAD cases, as shown in Figure 4-B. There was no significant correlation between the expression of p-STAT3 and other characteristics (Table 1).
Figure 4.
IHC staining for PD-L1/p-STAT3 in pulmonary adenocarcinoma specimens. (A) Positive expression of PD-L1 in pulmonary adenocarcinoma. (B) Positive expression of p-STAT3 in pulmonary adenocarcinoma. (C) Negative. The magnification is ×200. PD-L1 = programmed death-ligand 1, p-STAT3 = phosphorylated signal transducer and activator of transcription 3.
3.4. 18F-FDG PET/CT metabolic parameters of primary tumors
18F-FDG PET/CT imaging showed abnormal FDG uptake in all lesions. The average SUVmax of all patients was 10.49 ± 4.84, and the median value was 9.45 (2.50–30.20). The mean MTV of the primary tumors was 14.51 ± 20.97, and the median value was 7.20 (1.26–142.20). The mean TLG of the primary tumors was 118.67 ± 169.43, with a median value of 50.09 (2.91–993.34). The patients with positive PD-L1 expression have significantly higher SUVmax (P = .01), MTV (P = .00), and TLG (P = .00) than patients with negative PD-L1 expression. The mean + SD (PD-L1– vs PD-L1+) of SUVmax, MTV, and TLG were 8.63 ± 3.78 vs 12.35 ± 5.10, 4.11 ± 2.93 vs 24.92 ± 25.69, and 21.42 ± 14.25 vs 215.90 ± 196.39, respectively.
3.5. Survival analysis
The results of univariate analysis of prognosis (DFS) in all patients with surgically resected LUAD are shown in Table 2; univariate analysis of DFS prognosis showed that sex, PD-L1 expression, MTV, TLG, and stage were statistically significant (P = .023, P = .010, P = .007, P = .000, and P = .000, respectively), while age, smoking, p-STAT3, SUVmax, lactic dehydrogenase, carcinoembryonic antigen, and postoperative adjuvant therapy were not statistically significant. The statistical analyses of the Kaplan-Meier survival curves for stage, PD-L1, TLG, and MTV are shown in Figure 5.
Table 2.
DFS according to univariate analysis in 74 patients with surgical resection of lung adenocarcinoma.
| Factor | No. of patients | DFS | |
| Median survival time (months ± SE) | P value | ||
| Age | |||
| <60 | 45 (60.8) | 23.00 ± 1.65 | .486 |
| ≥60 | 29 (39.2) | 24.90 ± 1.83 | |
| Gender | |||
| Male | 38 (51.35) | 22.23 ± 3.40 | .023∗ |
| Female | 36 (48.65) | 25.07 ± 2.83 | |
| Smoking history | |||
| + | 28 (37.8) | 21.77 ± 2.12 | .232 |
| − | 46 (62.2) | 24.90 ± 3.47 | |
| PD-L1 | |||
| + | 46 (62.2) | 18.13 ± 1.78 | .010∗ |
| − | 28 (37.8) | 30.1 ± 2.47 | |
| p-STAT3 | |||
| + | 22 (29.7) | 23.00 ± 5.53 | .372 |
| − | 52 (70.3) | 24.00 ± 3.11 | |
| SUVmax | |||
| <12.60 | 55 (74.3) | 24.00 ± 2.98 | .096 |
| ≥12.60 | 19 (25.7) | 24.90 ± 6.46 | |
| MTV | |||
| <14.87 | 54 (73) | 26.80 ± 2.47 | .007∗ |
| ≥14.87 | 20 (27) | 18.00 ± 3.96 | |
| TLG | |||
| <90.58 | 49 (66.2) | 27.87 ± 3.20 | .000∗ |
| ≥90.58 | 25 (33.8) | 16.30 ± 2.48 | |
| LDH | |||
| <190 | 60 (81.1) | 23.93 ± 1.43 | .619 |
| ≥190 | 14 (18.9) | 27.87 ± 13.56 | |
| CEA | |||
| <5 | 43 (58.1) | 24.10 ± 1.86 | .922 |
| ≥5 | 31 (41.9) | 23.33 ± 5.02 | |
| Stage | |||
| I | 25 (33.8) | 42.20 ± 10.21 | .000∗ |
| II, IIIA | 49 (66.2) | 19.65 ± 1.65 | |
| Adjuvant therapy | |||
| − | 35 | 18.13 ± 2.19 | .583 |
| + | 39 | 29.47 ± 3.66 | |
CEA = carcinoembryonic antigen, DFS = disease free survival, LDH = lactic dehydrogenase, MTV = metabolic tumor volume, PD-L1 = programmed death-ligand 1, p-STAT3 = phosphorylated signal transducer and activator of transcription 3, SE = standard error, SUVmax = maximum standardized uptake values, TLG = total lesion glycolysis.
P < .05 considered statistically significant.
Figure 5.
Kaplan-Meier curve analyses of disease-free survival (DFS) of 74 patients with resected lung adenocarcinoma. (A) DFS according to staging. (B) Kaplan-Meier analysis of DFS according to PD-L1 expression. (C) Kaplan-Meier analysis of DFS according to the total lesion glycolysis (TLG). (D) Kaplan-Meier analysis of DFS according to the metabolic tumor volume (MTV). PD-L1 = programmed death-ligand 1.
3.6. Multivariate analysis of prognosis (DFS) in all patients with surgically resected lung adenocarcinoma
The results of the multivariate analysis of the prognosis (DFS) of all patients with surgically resected LUAD are shown in Table 3. Because MTV and TLG have a correlation coefficient of 0.85, there may be multiple collinearity; therefore, multivariate analysis revealed that PD-L1 expression, MTV, and staging were independent prognostic indicators for patients with surgically resected LUAD (P = .029, P = .026, and P = .003, respectively) when TLG was not included. Multivariate analysis revealed that PD-L1 expression, TLG, and staging were independent prognostic indicators for patients with surgically resected LUAD (P = .046, P = .022, and P = .005, respectively) when MTV was not included.
Table 3.
Multivariate analyses of prognostic factors for DFS in patients with surgical resection of lung adenocarcinoma.
| Factor | DFS | ||
| Hazard ratio (exp. B) | 95%CI | P value | |
| Gender | 1.571 | 0.920–2.061 | 2.680 |
| PD-L1 | 1.859 | 1.066–3.240 | .029∗ |
| MTV | 2.045 | 1.090–3.839 | .026∗ |
| Stage | 2.653 | 1.397–5.038 | .003∗ |
| Factor | DFS | ||
| Hazard ratio (exp. B) | 95%CI | P value | |
| Gender | 1.478 | 0.872–2.507 | .147 |
| PD-L1 | 1.736 | 1.011–2.981 | .046∗ |
| TLG | 1.950 | 1.099–3.461 | .022∗ |
| Stage | 2.550 | 1.324–4.914 | .005∗ |
CI = confidence interval, DFS = disease free survival, MTV = metabolic tumor volume, PD-L1 = programmed death-ligand 1, TLG = total lesion glycolysis.
P < .05 considered statistically significant.
4. Discussion
LUAD accounts for almost half of all lung cancer cases. Further research to explore the prognosis of patients with LUAD has important clinical significance. 18F-FDG PET/CT is an important tool for calculating the degree of tumor metabolism in NSCLC prognosis research. The main metabolic index currently used is the SUVmax. In this study, new 18F-FDG PET/CT volume metabolic parameters (MTV and TLG) were included. As the most commonly used 18F-FDG PET/CT metabolic parameter, the prognostic value of SUVmax for NSCLC has been controversial. The univariate and multivariate prognostic analyses in this study showed that there was no statistical difference between the SUVmax of pre-operative primary lesions and prognosis (DFS). This can be attributed to inter-study variations in tumor SUVmax that do not reflect actual changes in the metabolic uptake rate. Compared with SUVmax, MTV and TLG are new parameters that can reflect both the degree of FDG uptake and its scope. It is considered to be more accurate and stable in response to tumor burden, invasion, metastasis, and prognosis, and the results of our study are similar to recent findings,[14,15] in which high 18F-FDG PET/CT volume metabolic parameters (MTV or TLG) of primary tumors were independent factors affecting the poor prognosis (DFS) of LUAD with surgical resection.
Immunotherapy targeting PD-1/PD-L1 has been successfully used to treat a variety of malignant tumors, including LUAD. PD-L1 possesses prognostic capacities, and NSCLC patients with positive PD-L1 expression exhibit poor prognosis.[16] However, some studies did not show similar results,[17,18] and PD-L1 expression in NSCLC prognosis is controversial. Zhang et al[19] analyzed 143 cases of surgically resected LUAD (stage I–III) and found that PD-L1-positive patients had significantly poorer relapse-free survival (P = .001) and overall survival (OS) (P = .002). Song et al[20] studied the prognosis of 385 patients with surgically resected LUAD, and univariate analysis revealed that PD-L1 expression was associated with DFS, while multivariate analysis was not an independent prognostic factor for DFS and OS. Wu et al[21] analyzed the prognosis of 133 cases of surgically removed LUAD (stage I–IV) and found that PD-L1 expression was an independent prognostic factor for recurrence (relapse-free survival) and OS (P = .000 and P = .000, respectively). Our research showed that positive PD-L1 expression as a target for immunotherapy in LUAD possessed poor prognostic capacity for DFS. Thus, our results showed that 18F-FDG PET/CT metabolism parameters and PD-L1 expression may provide new information for prognosis and insights into clinical treatment options.
The high expression of PD-L1 in tumor tissues and its interaction with its receptor PD-1 weaken the immunogenicity of tumor cells and inhibit the production of tumor immune responses. In current clinical trials (CheckMate-057), an anti-PD-1/PD-L1 monoclonal antibody has been shown to be a potential drug for advanced NSCLC therapy, but not all patients are responsive.[22] The clinical trial results indicated that high PD-L1 expression was positively correlated with the efficacy of anti-PD-1/PD-L1 monoclonal antibodies.
In our study we found that patients with positive PD-L1 expression have significantly higher SUVmax (P = .01), MTV (P = .00), and TLG (P = .00) than patients with negative PD-L1 expression. We further analyzed the correlation between PD-L1 expression and 18F-FDG PET/CT parameters (SUVmax, MTV, and TLG) with chi-square test. There was no correlation between PD-L1 expression and 18F-FDG PET/CT parameters (chi-square test), which is inconsistent with the findings of previous studies[23] that showed that SUVmax was correlated with PD-L1 and DFS in NSCLC. This may be related to the heterogeneous expression of PD-L1, such as its expression not only in tumor cells but also in the interstitial tumor microenvironment. As a glucose analogue, FDG is transported into tumor cells and tumor-associated active immune cells such as TILs and TAMs[24,25]; thus, PET can provide useful information on the metabolic state of the tumor microenvironment. Glucose consumption in the tumor immune microenvironment can strictly limit metabolic T cells by inhibiting their effector function,[25,26] but a limitation of our study was that we did not analyze the expression of PD-L1 in the interstitial tumor microenvironment. The results may also be related to the selected cutoff value for PD-L1-positive expression; our IHC assay for PD-L1 utilized a cutoff of 5% TPS. Previous studies[27–29] reported PD-L1 staining with 1%, 5%, and 10% as expression thresholds, but no uniform threshold was defined and the scoring standards were different. Thus, the diversity of PD-L1 examination methods resulted in different conclusions. FDG hypermetabolism is not unique to malignant tumors, as it is also present in active inflammatory cells.[19,30] Thus, this non-specific uptake may be the reason why correlations between PET/CT parameters and PD-L1 expression were not observed in this study. Furthermore, this study was limited by its retrospective design and small sample size. Therefore, our study only suggested a potential role for 18F-FDG PET/CT in selecting candidate LUAD patients for treatment with checkpoint inhibitors. Further studies or new methods (Quantitative Lung Remodelling for Reliable Pulmonary Dosimetry[31] etc) are needed for confirming our findings or exploring new strategies.
STAT3 is most closely associated with tumors among members of the STAT family. p-STAT3 was found to play a crucial role in the occurrence and development of many carcinomas, and is also a critical regulator of immunosuppression[32] and has been shown to be associated with poor prognosis in various carcinomas[33]; however, its prognostic value in lung cancer has not yet been clarified. In our study, univariate and multivariate survival analyses showed that p-STAT3 was not an independent factor affecting the poor prognosis (DFS) of LUAD, similar to the results of Jiang et al,[34] who showed that high expression of p-STAT3 is not an independent prognostic factor for DFS and OS in NSCLC. Our study showed that the positive expression rate of p-STAT3 in LUAD was low (29.7%), which was significantly lower than that in previous reports, with 65%[35] and 54%[36] expression in NSCLC. Studies have shown that[37] EML4–ALK directly binds to the PDL1 promoter by p-STAT3 to increase the expression of PD-L1 in LUAD cell lines, suggesting that p-STAT3 may be associated with PD-L1 expression. It is beneficial to screen populations receiving targeted therapy, but no correlation between p-STAT3 and PD-L1 protein expression was observed in this study. There was also no statistically significant correlation between p-STAT3 expression and other parameters in this study.
5. Conclusion
18F-FDG PET/CT metabolic volume parameters (TLG ≥90.85 or MTV ≥14.87) were more helpful in prognostication than the conventional parameter (SUVmax), PD-L1 expression was an independent predictor of DFS in patients with resected LUAD. The present study did not show a direct association between metabolic parameters on 18F-FDG PET/CT and PD-L1 expression (chi-square test), but we found that patients with positive PD-L1 expression have significantly higher SUVmax (P = .01), MTV (P = .00), and TLG (P = .00) than patients with negative PD-L1 expression, which suggest a potential role for 18F-FDG PET/CT in selecting candidate LUAD patients for treatment with checkpoint inhibitors.
Acknowledgment
We thank Liwen Bianji, Edanz Editing China (www.liwenbianji.cn/ac) for editing the English text of a draft of this manuscript.
Author contributions
Conceptualization: Dalong Wang, Ping Li.
Data curation: Dalong Wang, Yingci Li, Xiaolin Chen.
Investigation: Yingci Li, Xiaolin Chen.
Methodology: Dalong Wang.
Project administration: Ping Li, Dalong Wang.
Resources: Yingci Li.
Software: Dalong Wang.
Supervision: Ping Li.
Validation: Xiaolin Chen.
Writing – original draft: Dalong Wang.
Writing – review & editing: Xiaolin Chen.
Footnotes
Abbreviations: 18F-FDG PET/CT = 18F-fluoro-2-deoxy-D-glucose positron emission tomography/computed tomography, DFS = disease-free survival, IHC = immunohistochemistry, LUAD = lung adenocarcinoma, SUVmax = maximum standardized uptake value, NSCLC = non-small-cell lung cancer, OS = overall survival, MTV = metabolic tumor volume, TLG = total lesion glycolysis, PD-1 = programmed cell death-1, PD-L1 = programmed death-ligand 1, STAT3 = signal transducer and activator of transcription 3, ROC = receiver operating characteristic curve.
How to cite this article: Wang D, Li Y, Chen X, Li P. Prognostic significance of volume-based 18F-FDG PET/CT parameters and correlation with PD-L1 expression in patients with surgically resected lung adenocarcinoma. Medicine. 2021;100:35(e27100).
DW, YL, and PL contributed equally to this work.
This work was supported by a grant from the Innovation Fund of Harbin Medical University (2020-KYYWF-1446).
The authors have no conflicts of interest to disclose.
All data generated or analyzed during this study are included in this published article [and its supplementary information files].
References
- [1].Bray F, Ferlay J, Soerjomataram I, Siegel RL, Torre LA, Jemal A. Global cancer statistics 2018: GLOBOCAN estimates of incidence and mortality worldwide for 36 cancers in 185 countries. CA Cancer J Clin 2018;68:394–424. [DOI] [PubMed] [Google Scholar]
- [2].Conde E, Angulo B, Izquierdo E, et al. Lung adenocarcinoma in the era of targeted therapies: histological classification, sample prioritization, and predictive biomarkers. Clin Transl Oncol 2013;15:503–8. [DOI] [PMC free article] [PubMed] [Google Scholar]
- [3].Hicks RJ, Kalff V, MacManus MP, et al. (18)F-FDG PET provides high-impact and powerful prognostic stratification in staging newly diagnosed non-small cell lung cancer. J Nucl Med 2001;42:1596–604. [PubMed] [Google Scholar]
- [4].Hoekstra CJ, Stroobants SG, Hoekstra OS, et al. The value of [18F]fluoro-2-deoxy-D-glucose positron emission tomography in the selection of patients with stage IIIA-N2 non-small cell lung cancer for combined modality treatment. Lung Cancer (Amsterdam, Netherlands) 2003;39:151–7. [DOI] [PubMed] [Google Scholar]
- [5].Hsu CC, Ho KW, Chang YH, Huang YC. Combining fluorine-18 fluorodeoxyglucose positron emission tomography and pathological risk factors to predict postoperative recurrence in stage I lung adenocarcinoma. Nucl Med Commun 2019;40:632–8. [DOI] [PubMed] [Google Scholar]
- [6].Paesmans M, Berghmans T, Dusart M, et al. Primary tumor standardized uptake value measured on fluorodeoxyglucose positron emission tomography is of prognostic value for survival in non-small cell lung cancer: update of a systematic review and meta-analysis by the European Lung Cancer Working Party for the International Association for the Study of Lung Cancer Staging Project. J Thorac Oncol 2010;5:612–9. [DOI] [PubMed] [Google Scholar]
- [7].de Langen AJ, Vincent A, Velasquez LM, et al. Repeatability of FDG uptake measurements in tumors: a metaanalysis. J Nucl Med 2012;53:701–8. [DOI] [PubMed] [Google Scholar]
- [8].Chen HH, Chiu NT, Su WC, Guo HR, Lee BF. Prognostic value of whole-body total lesion glycolysis at pretreatment FDG PET/CT in non-small cell lung cancer. Radiology 2012;264:559–66. [DOI] [PubMed] [Google Scholar]
- [9].Pardoll DM. The blockade of immune checkpoints in cancer immunotherapy. Nat Rev Cancer 2012;12:252–64. [DOI] [PMC free article] [PubMed] [Google Scholar]
- [10].Sacher AG, Gandhi L. Biomarkers for the clinical use of PD-1/PD-L1 inhibitors in non-small-cell lung cancer: a review. JAMA Oncol 2016;2:1217–22. [DOI] [PubMed] [Google Scholar]
- [11].Inghirami G, Chiarle R, Simmons WJ, Piva R, Schlessinger K, Levy DE. New and old functions of STAT3: a pivotal target for individualized treatment of cancer. Cell Cycle (Georgetown, Tex) 2005;4:1131–3. [DOI] [PubMed] [Google Scholar]
- [12].Yu H, Jove R. The STATs of cancer--new molecular targets come of age. Nat Rev Cancer 2004;4:97–105. [DOI] [PubMed] [Google Scholar]
- [13].Wang D, Zhang M, Gao X, Yu L. Prognostic value of baseline 18F-FDG PET/CT functional parameters in patients with advanced lung adenocarcinoma stratified by EGFR mutation status. PLoS One 2016;11:e0158307.Doi: 10.1371/journal.pone.0158307. [DOI] [PMC free article] [PubMed] [Google Scholar]
- [14].Melloni G, Gajate AM, Sestini S, et al. New positron emission tomography derived parameters as predictive factors for recurrence in resected stage I non-small cell lung cancer. Eur J Surg Oncol 2013;39:1254–61. [DOI] [PubMed] [Google Scholar]
- [15].Im HJ, Pak K, Cheon GJ, et al. Prognostic value of volumetric parameters of (18)F-FDG PET in non-small-cell lung cancer: a meta-analysis. Eur J Nucl Med Mol Imaging 2015;42:241–51. [DOI] [PubMed] [Google Scholar]
- [16].Wang A, Wang HY, Liu Y, et al. The prognostic value of PD-L1 expression for non-small cell lung cancer patients: a meta-analysis. Eur J Surg Oncol 2015;41:450–6. [DOI] [PubMed] [Google Scholar]
- [17].Konishi J, Yamazaki K, Azuma M, Kinoshita I, Dosaka-Akita H, Nishimura M. B7-H1 expression on non-small cell lung cancer cells and its relationship with tumor-infiltrating lymphocytes and their PD-1 expression. Clin Cancer Res 2004;10:5094–100. [DOI] [PubMed] [Google Scholar]
- [18].Tsao MS, Le Teuff G, Shepherd FA, et al. PD-L1 protein expression assessed by immunohistochemistry is neither prognostic nor predictive of benefit from adjuvant chemotherapy in resected non-small cell lung cancer. Ann Oncol 2017;28:882–9. [DOI] [PMC free article] [PubMed] [Google Scholar]
- [19].Zhang Y, Wang L, Li Y, et al. Protein expression of programmed death 1 ligand 1 and ligand 2 independently predict poor prognosis in surgically resected lung adenocarcinoma. Onco Targets Ther 2014;7:567–73. [DOI] [PMC free article] [PubMed] [Google Scholar]
- [20].Song Z, Yu X, Cheng G, Zhang Y. Programmed death-ligand 1 expression associated with molecular characteristics in surgically resected lung adenocarcinoma. J Transl Med 2016;14:188.Doi: 10.1186/s12967-016-0943-4. [DOI] [PMC free article] [PubMed] [Google Scholar]
- [21].Wu S, Shi X, Sun J, et al. The significance of programmed cell death ligand 1 expression in resected lung adenocarcinoma. Oncotarget 2017;8:16421–9. [DOI] [PMC free article] [PubMed] [Google Scholar]
- [22].Socinski MA, Jotte RM, Cappuzzo F, et al. Atezolizumab for first-line treatment of metastatic nonsquamous NSCLC. N Engl J Med 2018;378:2288–301. [DOI] [PubMed] [Google Scholar]
- [23].Wang Y, Zhao N, Wu Z, et al. New insight on the correlation of metabolic status on (18)F-FDG PET/CT with immune marker expression in patients with non-small cell lung cancer. Eur J Nucl Med Mol Imaging 2020;47:1127–36. [DOI] [PubMed] [Google Scholar]
- [24].Appelberg R, Moreira D, Barreira-Silva P, et al. The Warburg effect in mycobacterial granulomas is dependent on the recruitment and activation of macrophages by interferon-γ. Immunology 2015;145:498–507. [DOI] [PMC free article] [PubMed] [Google Scholar]
- [25].Chang CH, Qiu J, O'Sullivan D, et al. Metabolic competition in the tumor microenvironment is a driver of cancer progression. Cell 2015;162:1229–41. [DOI] [PMC free article] [PubMed] [Google Scholar]
- [26].Pearce EL, Pearce EJ. Metabolic pathways in immune cell activation and quiescence. Immunity 2013;38:633–43. [DOI] [PMC free article] [PubMed] [Google Scholar]
- [27].Mu CY, Huang JA, Chen Y, Chen C, Zhang XG. High expression of PD-L1 in lung cancer may contribute to poor prognosis and tumor cells immune escape through suppressing tumor infiltrating dendritic cells maturation. Med Oncol (Northwood, London, England) 2011;28:682–8. [DOI] [PubMed] [Google Scholar]
- [28].Mahoney KM, Sun H, Liao X, et al. PD-L1 antibodies to its cytoplasmic domain most clearly delineate cell membranes in immunohistochemical staining of tumor cells. Cancer Immunol Res 2015;3:1308–15. [DOI] [PMC free article] [PubMed] [Google Scholar]
- [29].Liu Y, Carlsson R, Ambjørn M, et al. PD-L1 expression by neurons nearby tumors indicates better prognosis in glioblastoma patients. J Neurosci 2013;33:14231–45. [DOI] [PMC free article] [PubMed] [Google Scholar]
- [30].Nicoleau S, Wojciak-Stothard B. Beyond thrombosis: the role of platelets in pulmonary hypertension. SciMed J 2020;2:243–71. [Google Scholar]
- [31].Xi J, Walfield B, Si XA, Bankier AA. Lung physiological variations in COVID-19 patients and inhalation therapy development for remodeled lungs. SciMed J 2021;3:198–208. [Google Scholar]
- [32].Ma JH, Qi J, Lin SQ, et al. STAT3 targets ERR-α to promote epithelial-mesenchymal transition, migration, and invasion in triple-negative breast cancer cells. Mol Cancer Res 2019;17:2184–95. [DOI] [PubMed] [Google Scholar]
- [33].Li W, Lee MR, Kim T, Kim YW, Cho MY. Activated STAT3 may participate in tumor progression through increasing CD133/survivin expression in early stage of colon cancer. Biochem Biophys Res Commun 2018;497:354–61. [DOI] [PubMed] [Google Scholar]
- [34].Jiang R, Wang X, Jin Z, Li K. Association of nuclear PIM1 expression with lymph node metastasis and poor prognosis in patients with lung adenocarcinoma and squamous cell carcinoma. J Cancer 2016;7:324–34. [DOI] [PMC free article] [PubMed] [Google Scholar]
- [35].Jiang R, Jin Z, Liu Z, Sun L, Wang L, Li K. Correlation of activated STAT3 expression with clinicopathologic features in lung adenocarcinoma and squamous cell carcinoma. Mol Diagn Ther 2011;15:347–52. [DOI] [PubMed] [Google Scholar]
- [36].Haura EB, Zheng Z, Song L, Cantor A, Bepler G. Activated epidermal growth factor receptor-Stat-3 signaling promotes tumor survival in vivo in non-small cell lung cancer. Clin Cancer Res 2005;11:8288–94. [DOI] [PubMed] [Google Scholar]
- [37].Koh J, Jang JY, Keam B, et al. EML4-ALK enhances programmed cell death-ligand 1 expression in pulmonary adenocarcinoma via hypoxia-inducible factor (HIF)-1α and STAT3. Oncoimmunology 2016;5:e1108514.Doi: 10.1080/2162402X.2015.1108514. [DOI] [PMC free article] [PubMed] [Google Scholar]