Journal of Immunology Research
Volume 2016 (2016), Article ID 9839685, 12 pages
http://dx.doi.org/10.1155/2016/9839685

Research Article

Evaluation of PD-L1 Expression in Tumor Tissue of Patients with Lung Carcinoma and Correlation with Clinical and Demographic Data

Gustavo Dix Junqueira Pinto,¹ Luciano de Souza Viana,2,3 Cristovam Scapulatempo Neto,3,4 and Sérgio Vicente Serrano1,5

¹Department of Medical Oncology, Barretos Cancer Hospital, Barretos, SP, Brazil
²Department of Oncology, Marcio Cunha Hospital, Fundação São Francisco Xavier, Ipatinga, MG, Brazil
³Post Graduation Program in Oncology, Barretos Cancer Hospital, Barretos, SP, Brazil
⁴Pathology, Clinicas Oncologicas Integradas, Rio de Janeiro, RJ, Brazil
⁵Barretos School of Health Sciences (FACISB), Barretos, SP, Brazil

Received 13 April 2016; Revised 20 July 2016; Accepted 18 August 2016

Academic Editor: Mario Clerici

Copyright © 2016 Gustavo Dix Junqueira Pinto et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract.

Lung cancer is the leading world cause of cancer-related death, in both genders, and smoking is the main etiological factor. The discovery of immune checkpoints corroborates the hypothesis that ligands presented in tumors modulate the mechanisms of carcinogenesis and the immune activity of tumor microenvironment. Among the most studied coregulatory molecules, PD-1 (programmed cell death 1) and its ligand PD-L1 (programmed cell death 1 ligand 1) are noteworthy. The present study aims to enhance the understanding of the tumor microenvironment of lung cancer patients who underwent surgery, by means of analysis of PD-L1 expression in tumor cells and in intratumoral immune cells (IICs). It was found that PD-L1 expression was more frequent in tumor cells than in IICs. Collective analysis by Tissue Microarray Assay (TMA) for PD-L1 expression in tumor cells and IICs did not reproduce the findings for separate individual analysis of tumor tissues. Patients with past history of smoking were more likely to express PD-L1 in tumor cells than those who never smoked. Patients with past history of smoking were less likely to have PD-L1 positive IICs compared to those who had never smoked. The immunohistochemical expression of PD-L1 in tumor cells and IICs did not correlate with survival.

1. Introduction

Lung cancer remains the leading cause of cancer death worldwide, for both men and women. Over half of people diagnosed with lung cancer die within one year of diagnosis and the 5-year survival is less than 18% [1].

In Brazil, according to 2016 estimates of INCA (National Cancer Institute), the incidence rate for tracheal, bronchus, and lung tumors will be 17330 new cases (8.1% of total) for men and 10890 cases (5.3% of total) for women [2].

Despite major advances in the personalized medicine, non-small-cell lung cancer is still related to poor prognosis.

Until recently, non-small-cell lung cancer was considered a nonimmunogenic tumor, but there is now evidence highlighting the integral role played by both inflammatory and immunological responses in lung carcinogenesis [3]. The discovery of immune checkpoints corroborates the hypothesis that ligands presented in tumors modulate the mechanisms of carcinogenesis and the immune activity of tumor microenvironment. New strategies in immunotherapy are targeting immune-modulating mechanisms that help tumor cells defend themselves against the immune system. Immune checkpoints are inhibitory pathways that maintain self-tolerance and protect the peripheral tissues by modulating the immune responses [4].

Recent studies show that tumor cells and antigen presenting cells modify tumor microenvironment through PD-1 receptor activities involving their ligands, PD-L1 and PD-L2 [5, 6]. PD-1 is a type I membrane protein composed of 268 amino acids which belongs to T-cell CD28/B7 family and is encoded by PDCD1 gene [7, 8]. It has an extracellular IgV domain, followed by a transmembrane region, and an intracellular tail, which contains two phosphorylation sites [9, 10] and is expressed on the surface of activated T cells, B cells, and macrophages [10].

Programmed cell death 1 ligand 1 (PD-L1) or B7 homolog 1 (B7-H1) is a type I transmembrane protein encoded by the CD274 gene [11].

The PD-1 function occurs primarily in peripheral tissues, where the T cells can contact their immunosuppressive ligands PD-L1 (B7-H1) and PD-L2 (B7-DC), which are expressed by tumor cells, stromal cells, or both [12–15]. It has been shown that inhibition of PD-1/PD-L1 interaction can exacerbate in vitro T cell response and mediate antitumor activity in preclinical models [14, 16].

More than that, PD-L1 expression may also vary according to different tumor microenvironments [17] and even to clinical and demographic data.

One recent study showed that PD-L1 expression was not associated with gender, histology, differentiation status, or lymph node metastasis. However, PD-L1 expression was increased in stage III NSCLC compared with stage I/II [18].

Other studies showed that PD-L1 expression was significantly associated with smoking [19–21], gender, higher tumor grade, advanced T status, advanced N status, advanced stage [19], and histology [22].

The role of PD-L1 expression neither as a prognostic nor as a predictive factor is controversial, being suggested in several studies [8, 23, 24]. Other studies do not confirm these findings [25, 26].

Indeed, recently, the KEYNOTE-001 trial of pembrolizumab (a humanized antibody that targets the programmed cell death 1 receptor) for advanced NSCLC showed a significantly favourable survival in patients with that PD-L1 expression greater than 50% in comparison to those with expression lower than 50% [27].

PD-L1 seems to be a mutable biomarker, with variable expression patterns related to heterogeneity in different areas within primary or metastatic lesions.

Histopathological material aging or the interval between tissue collection and treatment may also influence PD-L1 expression [28–30].

Positivity criteria for PD-L1 expression (machinery, antibodies, and cutoff) are not standardized yet and that certainly may contribute for all these discrepancies.

This study attempts to elucidate PD-L1 expression in lung tumor microenvironment. Possibly it may help to understand different clinical outcomes in lung cancer and establish more effective therapeutic measures.

2. Materials and Methods

2.1. Study Population

Tumor tissue samples and data were obtained from 177 cases. These patients underwent surgical resection of primary lung cancer between 2003 and 2014 at Barretos Cancer Hospital, Brazil. H&E stained sections were reviewed by a pathologist (CSN) and histological subtyping was assessed using the current World Health Organisation 2015 classification. Staging was undertaken according to the 7th edition AJCC tumor, node, metastasis (TNM) classification. The ethical use of human tissue for research was approved by the Institutional Review Board, and the design of this study followed the principles of the Declaration of Helsinki and also complied with the principles of good clinical practice.

2.2. Inclusion Criteria

Inclusion criteria include patients older than 18 years of both genders, diagnosed with non-small-cell lung cancer (adenocarcinoma, adenosquamous carcinoma, and squamous cell carcinoma), who underwent pneumonectomy, lobectomy, segmentectomy, or nodulectomy with available slides and paraffin blocks for histopathological analysis in the Pathology Department of Barretos Cancer Hospital.

2.3. Exclusion Criteria

Exclusion criteria include inappropriate histopathological material by either poor quality or shortage due to its use in other studies and patients with a current diagnosis of another primary malignancy in any location of the body other than nonmelanoma skin cancer or in situ carcinoma of the cervix.

2.4. PD-L1 Expression

PD-L1 immunohistochemistry membranous expression was assessed in TMA (Tissue Microarray Assay) with 2 cores of 1 mm in diameter of each tumor and also the expression was evaluated in whole tissue section of the same tumors (individual analysis).

2.5. TMA Blocks and Slides Construction

TMA blocks were made with MTA I (Manual Tissue Arrayer) device (Estigen, Tartu, Estonia), according to manufacturer’s specifications. TMA and all the paraffin blocks were sectioned with 4μ thick and the sections were transferred to positively charged glass slides.

At least one section per paraffin block was stained with hematoxylin-eosin in order to confirm the histology and to certify of tumor tissue availability in the slides by a pathologist and another slide was submitted to PD-L1 immunohistochemistry test.

2.6. Immunohistochemistry

Four micra thick sections (TMA and whole tissue sections) were dewaxed at 80°C for 20 minutes and then were transferred to Ventana BenchMark Ultra Autostainer (Ventana, Tucson, AZ, USA). Antigen retrieval was performed using Ventana Cell Conditioning solution 1 (pH: 8.5) for 64 minutes at 97°C. Anti-PD-L1 antibody (ab58810, Abcam, Cambridge, MA, USA) at titration of 1 : 25 was incubated for 60 minutes at 36°C. The detection of antigen antibody reaction was performed using UltraView DAB Universal Detection kit (Ventana, Tucson, AZ, USA). Strong membranous trophoblastic staining in the placenta was used as positive control. Tissue expression of PD-L1 was categorized dichotomically into negative (<5% membranous tumor cells expression) or positive (≥5% membranous tumor cells expression) [31] and also in groups according to the percentage of stained cells and staining intensity for a better sample description. The PD-L1 positive intratumoral immune cells (IICs) were graded as absent, 1+ (present until 10% of tumor surface), 2+ (present in 11–50% of tumor extension), and 3+ (present in more than 50% of tumor surface). Also, for statistical purposes PD-L1 expression was graded as present and absent.

2.7. Statistics

Data were described on the average, standard deviation, minimum, maximum, and quartiles for quantitative variables and frequency tables for qualitative variables. The agreement between the collective analysis technique or TMA (tissue microarray) and individual analysis was done using the Kappa coefficient to assess the reproducibility.

The correlation between clinical and demographic characteristics and PD-L1 expression in tumor cells and IICs was determined using the chi-square test (or Fisher’s exact test) for the qualitative characteristics. To check the overall association between covariates and PD-L1 marker, those that had lower value than 0.2 in the previous test were selected and subsequently adjusted into a logistics multiple regression model. For modeling, one feature (variable) was removed each time by prioritizing those with higher value, up to a set of significant variables.

For overall survival, the time between diagnosis and death for any reason (which is the event of interest) or last objective information of individuals who have not died yet was considered. To compare each feature and check the list of features with survival (one at each time), simple Cox regression was used. For joint evaluation between variables, those with value less than 0.2 were selected in simple analysis and adjusted in multiple Cox regression model. Then, modeling was continued as the same description in the logistic regression. To estimate the overall survival curve for PD-L1 expression the Kaplan-Meier method was used.

For survival analysis only overall survival was considered, because it is a retrospective study and there was no standardization in the follow-up of these patients in the past. In this study we considered the statistical significance of 0.05 and SPSS 21.0 software was used for statistical analysis.

3. Results

3.1. Demographic Data

In regard to demographic characteristics, as seen in Table 1, most patients were over 60 years old (96 cases; 54.2%), male (111 cases; 62.7%), white (140 cases; 79.1%), ECOG (Eastern Cooperative Oncology Group performance status) 0 (86 cases; 48.6%), with reported history of smoking (79 cases; 44.6%), and with no history of alcohol abuse (96 cases; 54.2%).

Table 1: Demographic characteristics.

Variable
Category

(%)

Age
<60 years
81
45.8

>60 years
96
54.2

Sex
Female
66
37.3

Male
111
62.7

Ethnicity
White
140
79.1

Non-white
32
18.1

Ignored
5
2.8

ECOG
0
86
48.6

1
46
26

Other
6
3.38

Ignored
39
22.02

Smoking
Absent
39
22

Active
57
32.2

Past
79
44.6

Ignored
2
1.1

Alcohol consumption
No
96
54.2

Active
45
25.4

Past
18
10.2

Ignored
18
10.2

ECOG: Eastern Cooperative Oncology Group performance status.

3.2. Clinical Data

The most common histological type was adenocarcinoma (115 cases, 65%) with II degree of differentiation (81 cases; 45.8%). Most of tumors had TNM Classification of Malignant Tumours lower than III. Stages I and II were observed in 62 patients (35%) and 53 patients (29.9%), respectively. Lobectomy was performed in 147 cases (83.1%). Adjuvant chemotherapy was performed in 34 cases (19.2%) (Table 2).

Table 2: Clinical data.

Variable
Category

(%)

Histological type
Adenocarcinoma
115
65

Squamous cell carcinoma
57
32.2

Other
5
2.8

Tumor grade
Grade I
5
2.8

Grade II
81
45.8

Grade III
50
28.2

Ignored
41
23.2

TNM staging
I
62
35

II
53
29.9

III
43
24.3

IV
19
10.7

Surgery type
Nodule extraction
4
2.3

Segmentectomy
12
6.8

Lobectomy
147
83.1

Pneumonectomy
14
7.9

Systemic treatment
No
121
68.4

Yes
55
31

Neoadjuvant chemotherapy
21
11.9

Adjuvant chemotherapy
34
19.2

Chemotherapy + radiotherapy
3
1.7

Ignored
1
0.6

Adjuvant radiotherapy
Yes
23
13

No
154
87

TNM staging: TNM Classification of Malignant Tumours.

3.3. PD-L1 Expression in TMA and Whole Tissue Section

PD-L1 was expressed in tumor cells and in IICs. Tumor cells had coarse chromatin, increased nuclei with irregular nuclear membrane, and abundant cytoplasm with ill-defined borders. However, intratumoral immune cells had loose chromatin, smaller fold nuclei without atypia, and variable cytoplasm, sometimes with dendritic expansions (Table 3).

Table 3: PD-L1 expression in conventional histological slides (individual analysis).

Cell type
Evaluation method
Graduation

%

Tumor cell
Intensity
Absence
97
54.8

Weak
52
29.3

Moderate
16
9

Strong
1
0.6

Missing
11
6.2

Tumor cell
Percentage (3 categories)
Absence
97
54.8

Up to 10%
6
3.4

From 11% to 50%
33
18.6

More than 50%
30
16.9

Ignored
11
6.2

Tumor cell
Percentage (2 categories)
Positive
67
37.9

Negative
99
55.9

Ignored
11
6.2

Intratumoral immune cells
Intensity
Absence
123
69.5

Weak
25
14.1

Moderate
15
8.5

Strong
3
1.7

Ignored
11
6.2

Intratumoral immune cells
Percentage (3 categories)
Absence
123
69.5

Up to 10%
3
1.7

From 11% to 50%
15
8.5

More than 50%
25
14.1

Ignored
11
6.2

Intratumoral immune cells
Percentage (2 categories)
Positive
43
24.3

Negative
123
69.5

Ignored
11
6.2

Positive: more than 5% stained cells.

Negative: less than 5% stained cells.

Ignored: staining problems preventing classification into positive or negative.

In Figures 1 and 2, there are photomicrographs of PD-L1 immunohistochemical expression in conventional histological slides in tumor cells and antigen presenting cells, respectively.

(a)

(b)

(c)

(d)

Figure 1: Photomicrographs of PD-L1 immunohistochemical expression in lung cancer tumor cells (magnification/scale bar: 400x/50μ). (a) Absence of PD-L1 expression; (b) negative PD-L1 expression (<5% of stained cells); (c) positive PD-L1 expression (≥5% stained cells); (d) Positive Control with placental tissue. Arrows show positive staining cells.

(a)

(b)

(c)

(d)

Figure 2: Photomicrographs of PD-L1 immunohistochemical expression in IICs in non-small-cells lung cancer (magnification/scale bar: 400x/50μ). (a) Absence of PD-L1 expression; (b) focal PD-L1 expression (<5% of tumor surface); (c) diffuse PD-L1 expression (>5% of tumor surface). Observe the dendritic cytoplasm of some cells; (d) Positive Control. Arrows show positive staining cells.

In Figure 3 there are photomicrographs of CD-68 immunohistochemical expression in IICs of non-small-cells lung cancer.

(a)

(b)

Figure 3: Photomicrographs of CD-68 immunohistochemical expression in IICs in non-small-cells lung cancer (magnification/scale bar: 400x/50μ). (a) Isolated IICs in a tumor area. (b) Positive CD-68 expression in a cluster of inflammatory cells.

Table 4 contains the results of PD-L1 expression by immunohistochemistry in TMA slides (collective analysis). Positive expression is observed in 58 cases (32.8%) in tumor cells and in 35 cases (19.8%) of IICs, that is, higher expression in tumor cells.

Table 4: PD-L1 expression in TMA slides (collective analysis).

Cell type
Evaluation method
Graduation

%

Tumor cell
Intensity
Absence
99
55.9

Weak
38
21.5

Moderate
16
9

Strong
4
2.3

Ignored
20
11.3

Tumor cell
Percentage (3 categories)
Absence
99
55.9

Up to 10%
0
0

From 11% to 50%
1
0.6

More than 50%
57
32.2

Ignored
20
11.3

Tumor cell
Percentage (2 categories)
Positive
58
32.8

Negative
99
55.9

Ignored
20
11.3

Intratumoral immune cells
Intensity
Absence
122
68.9

Weak
24
13.6

Moderate
6
3.4

Strong
5
2.8

Ignored
20
11.3

Intratumoral immune cells
Percentage (3 categories)
Absence
122
68.9

Up to 10%
4
2.3

From 11% to 50%
5
2.8

More than 50%
26
14.7

Ignored
20
11.3

Intratumoral immune cells
Percentage (2 categories)
Positive
35
19.8

Negative
122
68.9

Ignored
20
11.3

Positive: more than 5% stained cells.

Negative: less than 5% stained cells.

Missing: staining problems preventing classification into positive or negative.

3.4. Immunohistochemical Agreement of PD-L1 Expression in Individual Analysis (Whole Section) versus Collective Analysis (TMA)

As noted in Table 5, there was a fair agreement with Kappa index of 0.307 () when the immunohistochemical expression of PD-L1 in tumor cells in conventional histological slides (individual analysis) and TMA slides (collective analysis) was evaluated. Similar results were observed with PD-L1 expression in IICs in conventional histological slides (individual analysis) and IICs slides (collective analysis) with Kappa index of 0.328 ().

Table 5: Immunohistochemical agreement of PD-L1 expression in individual analysis versus collective analysis considering cell type.

Cell type
Kappa
Standard error
value

IICs
0.328
0.089
<0.001

Tumor cells
0.307
0.079
<0.001

Once the immunohistochemical expression of PD-L1 was not reproducible between TMA and whole tissue sections, all the analyses (univariate and multivariate) of correlation between PD-L1 expression and covariates (clinical data and demographic and other biomarkers) considered PD-L1 expression in whole tissue section.

3.5. Association of PD-L1 Expression with Demographic Data: Univariate Analysis

As noted in Table 6, patients whose tumors showed positive PD-L1 expression in tumor cells were mostly former smokers (36 cases; 55.4%) or active smokers (20 cases; 30.8%) with value = 0.044.

Table 6: PD-L1 expression in tumor cells and demographic data.

Variable
Categories
Negative
Positive
value

(%)

(%)

Age
<60
43
43.4
30
44.8
0.864

>60
56
56.6
37
55.2

Gender
Female
39
39.4
21
31.3
0.289

Male
60
60.6
46
68.7

Race
Non-white
18
18.8
11
16.7
0.734

White
78
81.2
55
83.3

ECOG
0
48
62.3
31
70.5
0.367

1
29
37.7
13
29.5

Smoking
No
29
29.3
9
13.8
0.044

Active
31
31.3
20
30.8

Former
39
39.4
36
55.4

Alcohol consumption
No
57
63.3
34
58.6
0.312

Active
25
27.8
14
24.1

Former
8
8.9
10
17.2

ECOG: Eastern Cooperative Oncology Group performance status.

As seen in Table 7, the correlation between PD-L1 expression in IICs and demographic data was not statistically significant.

Table 7: PD-L1 expression in IICs and demographic data.

Variable
Categories
Negative
Positive
value

(%)

(%)

Age
<60
50
40.7
23
53.5
0.144

>60
73
59.3
20
46.5

Gender
Female
41
33.3
19
44.2
0.202

Male
82
66.7
24
55.8

Race
Non-white
21
17.6
8
18.6
0.888

White
98
82.4
35
81.4

ECOG
0
57
64.8
22
66.7
0.845

1
31
35.2
11
33.3

Smoking
No
23
19
15
34.9
0.084

 Active
38
31.4
13
30.2

Former
60
49.6
15
34.9

Alcohol consumption
No
67
60.9
24
63.2
0.934

 Active
29
26.4
10
26.3

Former
14
12.7
4
10.5

ECOG: Eastern Cooperative Oncology Group performance status.

3.6. Correlation of PD-L1 Expression with Clinical Data

As seen in Table 8, the correlation between PD-L1 expression in tumor cells and clinical data was not statistically significant.

Table 8: PD-L1 expression in tumor cells and clinical data.

Variable
Categories
Negative
Positive
value

(%)

(%)

Histological type
Adenocarcinoma
68
68.7
40
59.7
0.412

Squamous cell carcinoma
28
28.3
25
37.3

Other
3
3
2
3

Tumor grade
I and II
50
62.5
31
64.6
0.813

III
30
37.5
17
35.4

TNM staging
I
36
36.4
23
34.3
0.756

II
27
27.3
23
34.3

III
26
26.3
14
20.9

IV
10
10.1
7
10.4

Neoadjuvant systemic treatment
No
86
86.9
61
91
0.407

Yes
13
13.1
6
9

TNM staging: TNM Classification of Malignant Tumours.

According to Table 9, among patients whose tumors had positive PD-L1 expression in IICs, most of them presented histologic type adenocarcinoma (35 cases; 81.4%) with statistical significance ( value = 0.022).

Table 9: PD-L1 expression in antigen presenting cells and clinical data.

Variable
Categories
Negative
Positive
value

(%)

(%)

Histological type
Adenocarcinoma
73
59.3
35
81.4
0.022

Squamous cell carcinoma
46
37.4
7
16.3

Others
4
3.3
1
2.3

Tumor grade
I and II
61
59.8
20
76.9
0.106

III
41
40.2
6
23.1

TNM staging
I
42
34.1
17
39.5
0.416

II
41
33.3
9
20.9

III
27
22
13
30.2

IV
13
10.6
4
9.3

Neoadjuvant systemic treatment
No
111
90.2
36
8.7
0.270

Yes
12
9.8
7
16.3

TNM staging: TNM Classification of Malignant Tumours.

3.7. Correlation of PD-L1 Expression with Clinical and Demographic Data: Multivariate Analysis

Patients with smoking history were more likely to present positive PD-L1 expression in tumor cells when compared to patients who had never smoked (OR = 3.356; 95% CI 1.368 to 8.230; value = 0.008) (Table 10).

Table 10: Multivariate analysis: PD-L1 expression in tumor cells.

Variable
Categories
OR
95% CI
value

LI
LS

Smoking
Never
1

0.03

Active
2.236
0.864
5.79
0.097

Past
3.356
1.368
8.23
0.008

After logistic regression, smoking was the only variable that remained significant related to PD-L1 expression in antigen presenting cells.

Patients with smoking history were less likely to present tumors with positive PD-L1 expression in IICs when compared to patients who had never smoked (OR = 0.383; 95% confidence interval from 0.162 to 0.908; and value = 0.029). The chance of positive PD-L1 expression in intratumoral immune cells was also lower for patients with active smoking when compared to patients who had never smoked but without statistical significance (OR = 0.525; 95% CI 0.212 to 1.297; and value = 0.169) (Table 11).

Table 11: Multivariate analysis: PD-L1 positive IICs.

Variable
Categories
OR
95% CI
value

Smoking
Never
1

0.090

Active
0.525
0.212–1.297
0.162

Past
0.383
0.162–0.908
0.029

Constant
0.652

0.198

3.8. Survival Curves Analysis according to PD-L1 Expression

The median overall survival of patients included in this study was 45 months (95% CI 33.23 to 56.83). Considering PD-L1 expression in tumor cells of conventional histological slides (individual analysis), there was a higher median overall survival for patients with tumors that had positive PD-L1 expression; however this difference was not statistically significant: 98.75 months (95% CI 21.26 to 176.24) versus 41.51 months (95% CI 30.05 to 52.98) with value = 0.254. Also, there was no statistically significant difference in the median overall survival when comparing PD-L1 expression in IICs: 49.50 months (95% CI 23.37 to 75.64) for patients with positive PD-L1 expression versus 41.51 months (95% CI 29.99 to 53.04) in patients with negative PD-L1 expression with value = 0.795 (Figures 4 and 5).

Figure 4: Overall survival according to PD-L1 expression in tumor cells. x-axis: time after diagnosis in months. y-axis: percentage of patients alive (total of 177 patients).

Figure 5: Overall survival according to PD-L1 positivity in IICs. x-axis: time after diagnosis in months. y-axis: percentage of patients alive (total of 177 patients).

4. Discussion

4.1. PD-L1 Expression Findings

According to this study, the frequency of PD-L1 expression in tumor cells was 37.9% of total cases, a little less than a recently published study that showed 53.1% of positivity [32], although the same antibodies and platforms have been used. There is a bias when comparing positivities related to different studies. There are different platforms (DAKO and VENTANA) to evaluate PD-L1 expression and different antibodies (28-8, 22C3, SP263, SP142, and MIH1, among others).

This evaluation can occur in different ways: continuous distribution and proportion of PD-L1 positive cells at any intensity [27], percentage expression (immunohistochemistry score) regardless of its intensity (more than 1% of stained cells: score 1, more than 5% stained cells: score 2, and more than 10% stained cells: score 3) [33], a combined score displaying a percentage for each intensity [34] by degree in membrane and/or cytoplasmic staining (e.g., Aqua Fluorescent Techniques), and protein concentration in Tissue Microarray Assay [35].

There is no standardized cutoff for positivity. Some studies have used 1%, 5%, 50%, or more to consider positive PD-L1 expression [36].

Therefore, it becomes extremely difficult to establish any relationship between studies as a consequence of no standard positivity criteria for PD-L1 expression, which involves the whole process, from chemical reactions machinery to dilutions of reactants and its reading interpretations. As seen in Table 12, there are different studies with different cutoffs for PD-L1 expression positivity.

Table 12: Immunohistochemistry for PD-L1 in clinical studies.

PD-L1 antibody
Cutoff for positivity of PD-L1 expression in tumor cell membrane
Percentage of tumor samples expressing PD-L1
Study reference

28-8
5%
49%
Grosso et al., JCO, 2013 [37]

R&D B7-H1
NR
52%
Gatalica et al., CEBP, 2014 [38]

MIH1
>10%
50%
Konishi et al., CCR, 2004 [39]

5H1
>1% versus >5% versus high score
21% (only CEC)
Marti et al., CCR, 2014 [30]

SP142
5%
60%

NR
1%
50%
Sun et al., JCO, 2014 [40]

22C3
≥50%
25%
Garon et al., NEJM, 2015 [27]

28-8
≥1%, ≥5%, ≥10%
53%, 36%, 25% (only  CEC)
Brahmer et al., NEJM, 2015 [33]

SP142
≥1%, ≥5%, ≥10%
68%, 37%, 16%

SP142
≥1%, ≥5%, ≥10%
56%, 28%, 13%
Herbst et al., Nature, 2014 [41]

Another important issue to be discussed is the feasibility of PD-L1 biomarker in order to be measured and analyzed in histopathological slides. Garon et al. noted PD-L1 deterioration in tumor samples cuts more than 6 months before staining [27]. According to Calles et al., there is deterioration of PD-L1 in blocks of more than three years [21]. In this study, staining was done less than a month after the cuts and due to this possible deterioration a lower cutoff of 5% was chosen.

A recent study showed that tumor microenvironment cells (including tumor cells, lymphocytes, and antigen presenting cells) do not express PD-L1 in a uniform way [36]. Smyth et al. argue that a successful cancer treatment must be precisely based on the stratification of tumor microenvironment and besides that it should not be restricted only to immune checkpoints but also to potentially involved cell types [42], as they are best studied and characterized.

Tumor microenvironment has a wide range of different cell types mainly represented by myeloid-derived suppressor cells, macrophages, dendritic cells, and T lymphocytes beyond tumor cells [43]. There is clearly a consensus that tumor microenvironment is a complex and dynamic structure so far as its presentation may vary for different time periods. The emergence of tumor cells leads to drastic changes that initiate immunity chronologically with an intrinsic induction of PD-L1 expression followed by adaptive immune tolerance and resistance to quantitative variations of various cell types, previously described [17].

4.2. Immunohistochemical Agreement between PD-L1 Expression in Individual Analysis and Collective Analysis (TMA)

This study analysis showed a fair (low) agreement between the two methods of immunohistochemistry (individual and collective), for PD-L1 expression evaluation in lung tumors. The medical literature has pointed to the importance that lung tumor heterogeneity may have regarding PD-L1 expression in small biopsies when compared to surgical specimens.

Small isolated samples from a particular tumor region gathered by biopsy or punches for TMA construction, for example, cannot represent PD-L1 expression for the tumor as a whole. This expression cannot be generalized, because of its intrinsic regional variability. Immunohistochemistry assessment of slides covering a tumor in its largest possible area, with the largest represented diameters, seems to provide a more representative description of real PD-L1 expression in lung tumors.

4.3. Correlation of PD-L1 Expression with Clinical and Demographic Data

In this study, tumors of patients with smoking history were more likely to positively express PD-L1 in tumor cells and they were also more likely to not express this biomarker in IICs. Although the influence of smoking in PD-L1 expression in tumor cells [21] has already been described, this is the first time that the possible influence of smoking in PD-L1 expression related to IICs is shown. Active smokers and former smokers were compared to nonsmokers (reference category after logistic regression). A possible explanation for the inverse relationship between smoking and PD-L1 expression in tumor cells versus IICs is the association between inflammatory proteins and such cell types with still unknown biological effects.

It is worth noting that changes in PD-L1 expression can also occur related to previous exposure to chemotherapy, a fact already demonstrated in urothelial carcinomas and lung cancer [44, 45]. The small number of patients undergoing neoadjuvant chemotherapy prevented this analysis in the present study.

4.4. Survival Curves Analysis according to PD-L1 Expression

There was no statistical significance related to PD-L1 expression and overall survival as previously described. Other studies show apparently not to be a predictive or prognostic value regarding PP-L1 expression [27, 46, 47]. However, in a recently published meta-analysis, after analyzing five trials with 877 patients with non-small-cell lung cancer, Zhou et al. concluded that PD-L1 expression may be related to a worse prognosis [48]. Nonetheless, only one of these studies included western patients outside China. Variations in the choice of different cutoffs for expression of positivity and the type of tissue sample may have contributed to discrepant results.

In summary, this study shows that, in a population of patients with non-small-cell lung cancer, the pattern of PD-L1 expression was heterogeneous, represented by two distinct cell types: the tumor cell (higher frequency) and IICs (lowest frequency). Positive PD-L1 expression was observed in 37.9% of tumor cells and in IICs of 24.3% of tumors.

TMA techniques (collective analysis) and conventional histological slides (individual analysis) showed fair agreement when they evaluated the immunoreactivity of PD-L1 expression in tumor cells (Kappa = 0.307) and in antigen presenting cells (Kappa = 0.328) of patients with non-small-cell lung cancer, value < 0.001, proving that TMA is not an adequate method to evaluate PD-L1 expression.

Former smokers had a higher PD-L1 expression in tumor cells when compared to those who had never smoked. In contrast, former smokers had a lower PD-L1 expression in IICs when compared to those who had never smoked. There was also no correlation between patterns of PD-L1 expression and survival in this population.

Competing Interests

The authors declare that they have no competing interests.

Acknowledgments

This work was supported by Grant CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico) 447590/2014-6.

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