PD-L1 Expression in Pituitary Neuroendocrine Tumors/Pituitary Adenomas

PD-L1 expression in PitNETs: Correlations with the 2022 WHO classification

Introduction

and research question: Prognostic factors to predict the behavior of pituitary neuroendocrine tumors (PitNET) are scarce. PD-L1 expression was associated with prognosis in other neuroendocrine neoplasms and we analyzed PD-L1 expression in PitNET, according to the 2022 WHO classification.

Material and methods

A retrospective analysis was performed. Immunohistochemistry was used to define PD-L1 expression, which was quantified as TPS (tumor proportion score). The primary outcome was to assess the correlation between PD-L1 expression and transcription factors (TF), namely T-pit, Pit-1, SF-1 and GATA-3. As secondary outcomes, we evaluated the association between PD-L1 expression and proliferation indexes.

Results

Eighty-eight patients were included. The largest group belonged to the SF-1-lineage (48%), followed by tumors of the Pit-1 lineage (32%) and T-pit lineage (17%). PD-L1 expression was associated with Pit-1 expression (p < 0.001) and with the somatotroph, lactotroph and mammosomatotroph subgroups. A TPS ⩾35% showed a 100% sensitivity for the mammosomatotroph subtype, while the optimal cut-off point was 20% for somatotroph and 15% for lactotroph tumors. PD-L1 expression was negatively associated with SF-1 and GATA3 expression(p < 0.001), with an optimal cut-point ≤5%. No association was found between PD-L1 expression and immunohistochemical proliferative factors but PD-L1 expression was associated with female sex and a younger age at diagnosis.

Conclusion

PD-L1 expression was associated with PIT-1 lineage, while it was downregulated in SF-1-lineage tumors. No correlation was found with proliferative factors. The role of PD-L1 expression in determining the biological behavior of PitNET remains debated and larger studies are necessary to further confirm these findings.

Diagnosis and Management of Aggressive/Refractory Growth Hormone-Secreting Pituitary Neuroendocrine Tumors

The majority of acromegaly and gigantism are caused by growth hormone-secreting pituitary neuroendocrine tumors (PitNETs). Most cases can be cured or controlled by surgery, medical therapy, and/or radiotherapy. However, a few of these tumors are resistant to traditional therapy and always have a poor prognosis. The title aggressive/refractory is used to differentiate them from pituitary carcinomas. To date, there is no definitive conclusion on how to diagnose aggressive/refractory growth hormone-secreting PitNETs, which may have slowed the process of exploring new therapeutical strategies. We summarized the literature described diagnosis and treatment of the disease. Potential disease markers and prospective therapies were also included.

The Role of Programmed Cell Death Ligand 1 Expression in Pituitary Tumours: Lessons from the Current Literature

BACKGROUND

Programmed cell death-1 (PD-1) and PD ligand-1 (PD-L1) expression predict the biological behaviour, aggressiveness, and response to immune checkpoint inhibitors in different cancers. We reviewed the published data on PD-L1 expression in pituitary tumours from the perspective of its biological role and prognostic usefulness.

SUMMARY

A literature review focused on PD-L1 expression in pituitary tumours was performed. Six immunohistochemistry-based studies which assessed PD-L1 positivity in pituitary tumours were included, encompassing 704 patients. The cohort consisted of 384 (54.5%) nonfunctioning tumours and 320 (43.5%) functioning pituitary tumours. PD-L1 expression was positive in 248 cases (35.2%). PD-L1 positivity rate was higher in functioning than in nonfunctioning tumours (46.3% vs. 26.0%; p < 0.001) but also higher in growth hormone-secreting tumours (56.7%) and prolactinomas (53.6%) than in thyrotroph (33.3%) or corticotroph tumours (20.6%). While proliferative pituitary tumours showed higher rate of PD-L1 positivity than non-proliferative tumours (p < 0.001), no association with invasion or recurrence was found.

KEY MESSAGES

PD-L1 is expressed in a substantial number of pituitary tumours, predominantly in the functioning ones. PD-L1 positivity rates were significantly higher in proliferative pituitary tumours in comparison to non-proliferative tumours, but no differences were found concerning invasive or recurrent pituitary tumours. More studies following homogeneous and standardised methodologies are needed to fully elucidate the role and usefulness of PD-L1 expression in pituitary tumours.

The Immune Microenvironment Landscape of Pituitary NeuroEndocrine Tumors, a Transcriptomic Approach

Pituitary neuroendocrine tumors (PitNET) are known to be variably infiltrated by different immune cells. Nonetheless, their role in pituitary oncogenesis has only begun to be unveiled. The immune microenvironment could determine the biological and clinical behavior of a neoplasm and may have prognostic implications. To evaluate the expression of immune-related genes and to correlate such expression with the presence of infiltrating immune cells in forty-two PitNETs of different lineages, we performed whole transcriptome analysis and RT-qPCR. Deconvolution analysis was carried out to infer the immune cell types present in each tumor and the presence of immune cells was confirmed by immunofluorescence. We found characteristic expression profiles of immune-related genes including those encoding interleukins and chemokines for each tumor lineage. Genes such as IL4-I1, IL-36A, TIRAP, IL-17REL, and CCL5 were upregulated in all PitNETS, whereas IL34, IL20RA, and IL-2RB characterize the NR5A1-, TBX19-, and POU1F1-derived tumors, respectively. Transcriptome deconvolution analysis showed that M2 macrophages, CD4+ T cells, CD8+ T cells, NK cells, and neutrophils can potentially infiltrate PitNET. Furthermore, CD4+ and CD8+ T cells and NK cells infiltration was validated by immunofluorescence. Expression of CCL18, IL-5RA, and HLA-B as well as macrophage tumor infiltration could identify patients who can potentially benefit from treatment with immune checkpoint inhibitors.

Aggressive and Metastatic Pituitary Neuroendocrine Tumors: Therapeutic Management and Off-Label Drug Use

Pituitary neuroendocrine tumors (PitNETs) are the most common pituitary tumors and the second most common brain tumors. Although the vast majority (>90%) are benign, a small percentage (<2%) are aggressive. These aggressive PitNETs (AgPitNETs) are defined by the presence of radiological invasion, a high rate of cell proliferation, resistance to conventional treatments, and/or a high propensity for recurrence. Lastly, there are the rare pituitary carcinomas, also known as metastatic PitNETs (MetPitNETs), which account for only 0.2% of cases and are defined by the presence of craniospinal or distant metastases. At present, there are no definitive factors that allow us to predict with certainty the aggressive behavior of PitNETs, making the therapeutic management of AgPitNETs a real challenge. Surgery is considered the first-line treatment for AgPitNETs and MetPitNETs. Radiation therapy can be effective in controlling tumor growth and regulating hormone hypersecretion. Currently, there are no approved non-endocrine medical therapies for the management of AgPitNETs/MetPitNETs, mainly due to the lack of randomized controlled clinical trials. As a result, many of the medical therapies used are off-label drugs, and several are under investigation. Temozolomide (TMZ) is now recognized as the primary medical treatment following the failure of standard therapy (medical treatment, surgery, and radiotherapy) in AgPitNETs/MetPitNETs due to its ability to improve overall and progression-free survival rates in responding patients over 5 years. Other therapeutic options include pituitary-targeted therapies (dopamine agonists and somatostatin analogs), hormonal antisecretory drugs, non-hormonal targeted therapies, radionuclide treatments, and immunotherapy. However, the number of patients who have undergone these treatments is limited, and the results obtained to date have been inconsistent. As a result, it is imperative to expand the cohort of patients undergoing treatment to better determine the therapeutic efficacy and safety of these drugs for individuals with AgPitNETs/MetPitNETs.

Role of Tumor Microenvironment in Pituitary Neuroendocrine Tumors: New Approaches in Classification, Diagnosis and Therapy

Adenohypophysal pituitary tumors account for 10-15% of all intracranial tumors, and 25-55% display signs of invasiveness. Nevertheless, oncology still relies on histopathological examination to establish the diagnosis. Considering that the classification of pituitary tumors has changed significantly in recent years, we discuss the definition of aggressive and invasive tumors and the latest molecular criteria used for classifying these entities. The pituitary tumor microenvironment (TME) is essential for neoplastic development and progression. This review aims to reveal the impact of TME characteristics on stratifying these tumors in view of finding appropriate therapeutic approaches. The role of the pituitary tumor microenvironment and its main components, non-tumoral cells and soluble factors, has been addressed. The variable display of different immune cell types, tumor-associated fibroblasts, and folliculostellate cells is discussed in relation to tumor development and aggressiveness. The molecules secreted by both tumoral and non-tumoral cells, such as VEGF, FGF, EGF, IL6, TNFα, and immune checkpoint molecules, contribute to the crosstalk between the tumor and its microenvironment. They could be considered potential biomarkers for diagnosis and the invasiveness of these tumors, together with emerging non-coding RNA molecules. Therefore, assessing this complex network associated with pituitary neuroendocrine tumors could bring a new era in diagnosing and treating this pathology.