PD-L1 Expression in Medullary Thyroid Carcinoma and Its Association with Clinicopathological Findings
Yasemin KEMAL1 , Sultan ÇALIŞKAN2 , Seda GUN2 , Mehmet KEFELI2
1Department of Medical Oncology, Istinye University, Faculty of Medicine, İSTANBUL, TURKEY
2Department of Pathology, Ondokuz Mayıs University, Faculty of Medicine, SAMSUN, TURKEY
Keywords: Medullary thyroid carcinoma, Immunotherapy, Programmed death-ligand 1 (PD-L1), Clinicopathological characteristics
Objective: Medullary thyroid carcinoma (MTC) is a rare tumor originating from parafollicular C cells. It has more aggressive biologic behavior than differentiated thyroid carcinomas, and it is insensitive to treatment with radioactive iodine. Vandetanib and cabozantinib are the newly approved tyrosine kinase inhibitors in advanced stages, but novel effective systemic therapeutics could be crucial and needed for the clinical management of these patients. We aimed to evaluate the Programmed death-ligand 1 (PD-L1) expression, which is a novel immunotherapy target, in our MTC cohort, and determine whether it has an association with clinical and pathological features.
Material and Method: This retrospective study involved 41 cases of MTC with a median follow-up of 54 months. PD-L1 monoclonal antibody (SP263 clone) was investigated immunohistochemically. Complete and/or partial membranous staining pattern in more than 1% of tumor cells was considered positive. The correlations of PD-L1 expression with clinicopathologic and prognostic features were analyzed.
Results: PD-L1 positivity was detected in 5 (12.2%) of 41 tumors. The extent of PD-L1 staining was low (<5%) for all tumors. There was no clinicopathologic and prognostic relevance regarding PD-L1 expression in our MTC patients.
Conclusion: Although PD-L1 expression could be a potential biomarker to predict the prognosis of various cancers and response to checkpoint inhibitors, we did not find any significant correlation between PD-L1 expression and clinicopathologic features in our cases. Studies with larger patient numbers are still required to perform a more comprehensive analysis.
Medullary thyroid cancer (MTC) is a rare neuroendocrine
tumor originating from calcitonin-producing parafollicular
C cells of the thyroid gland. It has an aggressive clinical
course and a worse prognosis than differentiated thyroid
carcinomas, and the 10-year survival rate is reported as
. The prognosis is usually associated with the
clinicopathological findings (i.e., age, gender, the presence
of local tumor invasion, lymph node metastases, and
distant metastases) and the mutant codon region of the
RET gene (i.e., M918T) 3-7
. The current initial treatment
approach of MTC is total thyroidectomy and central
compartment lymph node dissection. Systemic treatment
is considered for patients with significant tumor burden
or progressive or unresectable metastatic disease. Because
cytotoxic chemotherapeutics, selective RET inhibitors, and
multi-kinase inhibitors have low/modest response rates
and significant toxicities, and new and effective treatment
agents are needed for advanced progressive MTC 3
Immunotherapy with checkpoint inhibitors targeting
Programmed death receptor-1 (PD-1) and Programmed death-ligand 1 (PD-L1) have been used effectively for the
treatment of various tumors as a promising alternative for
cancer management and found to be associated with the
prognosis of the patients 7-12. The relationship between
PD-L1 and thyroid carcinoma was also investigated;
however, nearly all these studies included differentiated
thyroid carcinomas 13-20. The knowledge about the PDL1
expression in MTCs is limited; it has been evaluated
only in a few studies to date. In this study, we aimed to
investigate PD-L1 expression in MTC patients treated at
our university hospital. We also investigated the association
between PD-L1 positivity and the clinicopathological
characteristics of the patients.
A total of 41 MTC patients diagnosed between 2009 and
2018 were included in the study. Institutional REB (research
ethics board) approval was obtained. The diagnosis
of MTC is proved based on cytomorphologic features
accompanying diffuse immunoreactivity for monoclonal
CEA and calcitonin. Four μm sections were taken from
paraffin blocks representing selected patients, and sections were investigated with PD-L1 monoclonal antibody
(SP263 clone, Ventana Medical Systems, Inc., AZ) using a
Benchmark XT automated staining device (Roche, Ventana
Medical Systems). Because MTCs usually have very few
tumor-associated inflammatory cells, PD-L1 expression
was determined by using the tumor proportion score
rather than the combined positive score. In all sections,
PD-L1 expression in tumor cells was evaluated. PD-L1-
expressing tumor cells were scored as a percentage of total
tumor cells. Complete and/or partial membranous staining
pattern in tumor cells was considered positive. Positive
staining in more than 1% of tumor cells was determined as
the threshold value for positive staining. The patients with
positive PD-L1 staining were separated into low (1-5%)
and high (>5%) PD-L1 positive groups. The PD-L1 stained
slides were evaluated by a pathologist without knowledge
of the clinicopathologic features. Normal human term
placental tissue was used as the control according to the
manufacturers suggestion because it contains positive and
negative staining elements for the PD-L1 protein.
PD-L1 staining was compared with the following parameters:
age, gender, tumor diameter and localization, pT
and pN status, multifocality, bilaterality, the presence of
capsule, capsule invasion, surgical margin status, vascular
invasion, lymphatic invasion, perineural invasion, extrathyroidal
extension, lymph node involvement, C cell hyperplasia,
the presence of chronic lymphocytic thyroiditis, and
recurrence. Histopathologically or cytologically confirmed
relapses of the patients with normal radiological findings
and normal-decreased serum calcitonin levels after initial
surgery were considered recurrence. Recurrence was found
in nine out of 41 patients, and all of them were detected at
the regional lymph nodes.
SPSS, version 20 was used for statistical analysis.
Fishers exact test were used to compare the PD-L1
immunohistochemical results with parameters such as age,
gender, tumor size, multifocality, surgical margin status, pT
stage, pN stage, and recurrence. In the statistical analysis,
NA (not-available) data were considered missing data, and
statistical analysis was performed by excluding these data.
A p-value of less than 0.05 was considered significant.
The age range at diagnosis of the patients was between 12
and 94 years (mean age: 47.8; median age: 48) for the overall
cohort. Twenty-four patients were female, and seventeen
patients were male. The mean tumor diameter was 22.2
±12.7 mm (range: 1-55 mm). Twenty-four tumors (58.5%)
were unifocal. According to the TNM stage, twenty-three
patients were pT1, sixteen patients were pT2, and two patients were pT3 status. Lymph node dissection was
performed for 21 out of 41 patients (51.2%). Nine patients
were pN0, six patients were pN1a, six patients were pN1b,
and twenty patients were pNx. Recurrence was seen in
nine of 41 patients, and all of them were detected at the
regional lymph nodes. None of the 41 patients had distant
metastases at diagnosis. All the patients were alive during
the data collection phase.
PD-L1 positivity of tumor cells was detected in 5 (12.2%)
of 41 tumors (Figure 1A-D, 2A-D). The extent of PD-L1
staining was low (1-5%) for all tumors. The age range at the
time of diagnosis in PD-L1 positive patients was between
32 and 67 years (mean age: 47.8; median age: 35). One
of the PD-L1 positive patients was male, and four were
female. The tumor was located in the right lobe in three
of the PD-L1 positive patients and in the left lobe in two
patients. Multifocality, bilaterality, and separate tumor foci
were observed in one patient. The tumor was encapsulated
in two patients, and all tumors had capsule invasion. In
all PD-L1 positive tumors, the surgical margin was intact,
and no perineural invasion or extrathyroidal extension was
observed. Three patients had C cell hyperplasia, and two
patients had lymph node metastasis. One of five PD-L1
positive patients also had a chronic lymphocytic thyroiditis
background. There was no correlation between PD-L1
negative and positive patients based on clinicopathological
characteristics, including age, sex, tumor size, multifocality,
surgical margin, pT stage, pN stage, initial lymph
node metastasis, recurrence, and relation with chronic
lymphocytic thyroiditis (p>0.05). Correlation between PDL1
expression and clinicopathological characteristics are
shown in Table I and II. There was no clinicopathologic
and prognostic relevance regarding PD-L1 expression in
this cohort. The median follow-up time was 54 months
(min. 15 months, max. 127 months).
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|Figure 1: Focal (<5%) membranous PD-L1 expression in medullary thyroid carcinomas (A,C: H&E; x20&40; B,D: PD-L1; x20&40).
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|Figure 2: PD-L1 negative medullary thyroid carcinomas (A,C: H&E; x20&40; B,D: PD-L1; x20&40).
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|Table I: Clinicopathological features of 41 medullary thyroid carcinomas according to PD-L1 status.
Click Here to Zoom
|Table II: Clinicopathological features of PD-L1 positive medullary thyroid carcinomas.
The expression of PD-L1 in thyroid cancers originating
from follicular cells has been investigated in many recent
studies, and the rates of PD-L1 positivity vary between 6.1%
and 82.5% in thyroid carcinomas originated from follicular
. The investigator found that PD-L1 positivity was
higher in anaplastic thyroid carcinoma than in papillary
thyroid carcinoma and follicular thyroid carcinoma, and it
is associated with a worse prognosis and aggressive tumor
. Some studies have indicated that it could
be a potential target in the management of thyroid cancer
with high expression of PD-L1 13-20
. In the recent metaanalytic
study, Girolami et al. provided a systematic review
of the published data relevant to follicular epithelial-derived thyroid carcinoma. They reviewed 445 manuscripts and
included 15 of them that had sufficient data to perform a
quantitative analysis. The studys results indicated that PDL1
expression was significantly associated with reduced
disease-free survival, but no association was found with the
overall survival. Besides, they found a significant association
between PD-L1 expression in papillary thyroid carcinomas
in terms of underlying chronic lymphocytic thyroiditis
and BRAF V600E mutation status 21
. Nevertheless, the
knowledge of the relationship between PD-L1 and MTC
is less than the tumors originating from follicular cells;
only a few studies have evaluated PD-L1 positivity in MTC
Bongiovanni et al. first investigated the expression of PDL1
in MTC, and PD-L1 expression was detected in only 1
of 16 MTC patients (6.2%) 22. In the second study, Bi et
al. reported 21.8% positivity among 81 MTC patients 23.
More recently, a large cohort study revealed that 29 of 201 patients (14.4%) showed positive staining by the PD-L1
antibody 24. In another study, Ingenwerth et al. reported
that neither tumor cell nor lymphocytes/macrophages
showed PD-L1 expression in 38 MTC patients in their
cohort 25. In our study, the percentage of PD-L1
expression was 12.2%. The positive staining rate between
these five studies varies between 0% and 21.8%, and this
alteration may be due to differences in the evaluation
method and antibodies used. In those studies, the 22C3
clone was used in two studies, and the SP263 clone was
used in three studies, including the current study. In nonsmall
cell lung carcinomas, reported PD-L1 expression for
the clone of SP263 was higher than for the clone of 22C3
26. Therefore, the use of different clones could affect the
positivity of tumor cells in studies. Different case numbers
and clinicopathological features of the patients (e.g.,
different numbers of included progressive metastatic or
advanced stage patients in the cohorts) in studies may also cause staining rates to differ. A comprehensive summary of
the published studies of the PD-L1 expression in medullary
thyroid carcinoma is shown in Table III.
Click Here to Zoom
|Table III: Comprehensive summary of the published studies of the PD-L1 expression in medullary thyroid carcinoma.
Considering the relationship between PD-L1 positivity and
the clinicopathological features of patients, different results
have been reported in previous studies. In our cohort, there
was no association between clinicopathologic features and
PD-L1 expression. Bongiovanni et al. reported only one PDL1
positive patient who had a microcarcinoma (0.8cm) and
who was reported as alive at the last follow-up 22. Bi et al.
reported that PD-L1 positivity was significantly correlated
with distant metastases at surgery, and co-expression of
PD-1 and PD-L1 is associated with a more advanced TNM
stage 23. Similarly, in the study conducted by Shi et al.,
PD-L1 positive patients were associated with aggressive
clinicopathological features such as larger tumor size,
lymph node metastases, and advanced TNM staging 24.
Although the rate of PD-L1 positivity in MTC patients
varies in previous studies, some studies have emphasized
that it can be a predictor for locally advanced disease and
PD-1/PD-L1 interaction plays a critical role in the
immunosuppressive tumor microenvironment. This
interaction inhibits T-cell activation and tumor lysis. It
may explain the aggressive disease course and the higher
stage. PD-L1 is thought to act as a predictive marker for
anti-PD-1/PD-L1 immunotherapy, and there are several
ongoing immunotherapy trials with clinical promise in
thyroid cancers. According to a recent meta-analysis,
PD-L1 positivity is correlated with poor prognosis in
non-medullary thyroid cancer patients, and this result is
consistent with many other human cancers 27.
There is no effective treatment option that prolongs
overall survival in advanced stage MTC patients. Cytotoxic chemotherapy has low response rates and durations.
Vandetanib and cabozantinib are the newly approved
tyrosine kinase inhibitors for the treatment of the patients
at advanced stages 1. Anti-PD-1/PD-L1 therapies may
provide additional treatment options for MTC patients.
More recently, in a phase 1b study, Mehnert et al. reported
that the anti-PD-L1 antibody, pembrolizumab, may have
an antitumor activity with an acceptable safety profile in a
small percentage of advanced differentiated thyroid cancer
patients 28. As with many other types of cancer, there
is no clear predictive biomarker in thyroid cancers that
indicates which patient will benefit more from checkpoint
inhibitors. Also, PD-L1 expression is not a pure predictive
biomarker for anti-PD-1/PD-L1 antibodies, but it could
be useful in some cancer subtypes. In a phase one study
performed by Yamamoto et al., nivolumab (anti-PD-1
antibody) found a partial response in one MTC patient.
Another ongoing phase II trial (NCT03072160) explores
the efficacy of pembrolizumab in recurrent and metastatic
Our study is the fifth study evaluating the PD-L1 positivity
in MTC patients in English literature, but this study also
has some limitations. This study has a retrospective design,
and the number of patients is relatively small. There were
only 5 PD-L1 positive tumors in our cohort, and it may not
be sufficient for interpretation in the correlation analysis.
Additionally, we do not have enough information about
some of the patients distant metastasis status at the time
of diagnosis. However, the median follow-up time was 54
months (min. 15 months, max. 127 months) for our cohort,
and all the patients were alive during the data collection
In conclusion, PD-L1 overexpression is associated with
recurrence and poor prognosis in various cancers, but we
did not find any significant correlation between PD-L1
expression and clinicopathologic features in our cohort.
The reason may be the lack of a significant number of
biologically aggressive and advanced stage (pT4) MTCs
in our cohort. Further studies with larger patient numbers
with advanced stage disease are still required to perform a
more comprehensive analysis.
CONFLICT of INTEREST
Authors declare no conflict of interest.
Concept: YK, MK, Design: YK, MK, Data collection
or processing: SG, SÇ, Analysis of Interpretation: SÇ,
MK, Literature search: YK, MK, SÇ, Writing: YK, MK,
Approval: MK, SÇ.
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