Original ArticleImmune Microenvironment of Primary and Recurrent Craniopharyngiomas: A Study of the Differences and Clinical Significance
Introduction
Craniopharyngioma (CP) occurs mainly in the 5- to 14-year and 50- to 74-year age groups, accounting for 2% to 5% of primary intracranial tumors and more than half of saddle area tumors in children.1, 2 The histological subtypes of CP include adamantinomatous craniopharyngioma (ACP) and papillary craniopharyngioma (PCP). ACP may be diagnosed in all ages, whereas PCP invariably occurs in adults and is rarely observed in children. Although CP is a benign tumor, it is adjacent to the pituitary, hypothalamus, optic nerve, and internal carotid artery. In addition, its clinical manifestations are complicated and it is associated with a high rate of relapse. Studies investigating CP involved various aspects, such as molecular pathology, cancer stem cells, patient-derived xenografts, and molecular targeted therapy.3 Using new-generation sequencing, it was confirmed that ACP primarily carries CTNNB1 mutations, whereas PCP mainly carries BRAF mutations. Use of a BRAF inhibitor achieved positive results in the treatment of PCP and it is currently under investigation in clinical trials.4, 5
The proliferation of tumors is based on changes in its molecular biology. More recent studies also indicated that the tumor microenvironment plays a key regulatory role in the progression of intracranial malignant tumors, and that targeted therapy against the components of the microenvironment may be performed to achieve certain clinical effects.6 Nevertheless, studies investigating the immune microenvironment of CP are currently limited. In this study, we collected specimens obtained from patients with CPs. For each patient, specimens for both primary and recurrent CPs were collected. We analyzed the distributions of M2 macrophages (main cells of tumor tissue), CD8+ T cells (immune killer cells), programmed cell death 1 (PD-1)/programmed cell death 1 ligand 1 (PD-L1) (immune checkpoint), and Ki67 (proliferation marker), to understand the differences between the immune microenvironments of primary and recurrent CPs. In addition, we investigated the relationship of immune microenvironmental indicators with clinical characteristics.
Section snippets
Patients
This study retrospectively analyzed a total of 52 tumor specimens of primary and recurrent CPs (26 specimens each) and clinical data of 26 patients from September 2008 to February 2017. Clinical data included demographics, clinical symptoms, imaging, surgical conditions, pathological types, and recurrence time (Table 1, Figures 1 and 2). The patients were treated only with surgical resection and did not receive other treatments such as radiation therapy or intracapsular interventions. Recurrent
Characteristics of Immune Microenvironments in Primary and Recurrent CPs
M2 macrophages were mainly found in the stroma and significantly distributed around the perivascular areas and close to tumor cells. Compared with primary CPs, the abundance of M2 macrophages in recurrent CPs was significantly increased. In contrast, the number of CD8+ T cells in recurrent CPs was not significantly different from that observed in primary CPs. Ki67-positive cells were mainly distributed in basal cells and in whorls of tumor epithelium. Moreover, concerning the expression of
Discussion
The tumor microenvironment is composed of tumor cells, extracellular matrix components, immune cells, and the tumor vascular system. It plays an important role in tumor progression and metastasis of intracranial primary and metastatic tumors.11 Tumor-associated macrophages are derived from monocytes in the blood, which are recruited into tumor tissues by various signals, cytokines of tumor cells, and cytokines of tumor microenvironment, polarizing into M1 and M2 types with different functions
Conclusions
Comparisons between primary and recurrent CPs in the same patients indicated that the immune microenvironment of recurrent CPs was significantly changed. The abundance of M2 macrophages in primary CP may suggest a shortened time for tumor recurrence. Consequently, the frequency of follow-up examinations in these patients should be increased. In recurrent tumors, the microenvironment indicators with increased expressions are correlated with poor prognosis, higher chance of immune escape, and
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Conflict of interest statement: The authors declare that the article content was composed in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.