Primary undifferentiated pleomorphic sarcoma in oral-maxillary area: retrospective study and molecular analysis

Background: Undifferentiated pleomorphic sarcoma (UPS) in oral-maxillary area is rarely reported. Herein, we aimed to investigate the clinical characteristics, treatment strategies, prognosis, and molecular features of the oral-maxillary UPS. Methods: Retrospectively, we reviewed the UPS patients who were diagnosed and treated in our department. The medical histories, imaging features, histopathological characteristics, treatment strategies, clinical outcomes were summarized and analyzed. Besides, the molecular features were demonstrated by whole exonic sequencing. Results: Totally, 10 cases with primary oral-maxillary UPS were included. The rapidly progressive UPS can easily develop at advanced and life-threatening stage, especially concerning the complex anatomical structures and spaces in the oral-maxillary area. The finial diagnosis for UPS greatly depends on histological findings and immunohistochemistry under the exclusion of all the possible differential diagnosis. Retrospectively, the treatment strategies for the involved cases still referred to those of oral squamous cell carcinoma. Statistically, the median overall survival (OS) for all the included cases was 7.75 months (range: 5-17 months). Comparatively, 3 cases had improved OS (median survival: 17 months, range: 17-18 months) experienced PR/SD with neoadjuvant chemotherapy (anlotinib). Cancer driver genes detection revealed GBP4 as a candidate driver gene for the oral-maxillary UPS. Additionally, a missense mutation in gene PIK3CA (p.E545K) was also identified. Conclusion: Our findings can greatly expand the knowledge about the oral-maxillary UPS, and provide molecular evidences to improve the therapeutic options for the oral-maxillary UPS. Further studies are warranted to validate our discoveries on the oral-maxillary UPS.


Introduction
Undifferentiated pleomorphic sarcoma (UPS) has been established as an entity in the WHO-classification of soft tissue sarcoma since 2002 [1][2][3]. UPS is very rare and constitutes less than 5% of all sarcomas in adults, most of which occurs in the extremities and the trunk of elderly patients [4,5]. The etiology for UPS is unknown, and the clinical features of UPS are not specific [6]. Till now, the clinical characteristics and therapeutic experiences of primary UPS are limited, and patients suffered from UPS experience a poor prognosis [7,8].
Accordingly, head and neck localization of UPS is rare, with an incidence ranging from 4% to 10% [9]. The most frequent involved sites for UPS in the head and neck area are neck and parotid, followed by scalp, face, anterior skull base and orbit [9]. Primary UPS in the oral-maxillary area is exceedingly rare. Anatomically, the oral-maxillary area is a key site in head and neck. Clinical practice indicates that the outcomes for the patients with oral-maxillary are extremely poor. So, it is necessary to get to know the oral-maxillary UPS. In this study, we managed to collect the primary oral-maxillary UPS treated in our department, retrospectively. The clinicopathological characteristics and the improved treatment strategies for the involved primary UPS were summarized and analyzed. Besides, the molecular features for the primary oral-maxillary UPS were preliminarily demonstrated by whole exonic sequencing (WES).

Patients
Retrospectively, we reviewed and collected the UPS patients who were pathologically diagnosed and experienced combined treatment between 2015 and 2020 at the Department of Oral Maxillofacial-Head and Neck Oncology, Shanghai Ninth People's Hospital. To be included in this study, the following criteria were met for each case: (a) primary/recurrent UPS in the oral-maxillary area; (b) intact medical histories of diagnosis and treatments; (c) intact histopathological data; (d) intact imagelogical records; (e) follow-up information as complete as possible. The following cases were excluded: (a) the metastasized/secondary UPS involved the oral-maxillary areas; (b) patients with only histopathological biopsy and without subsequent treatments. This study was approved by the Medical Ethics Committee of the Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine (SH9H-2020-T321-1).
The demographic data of the involved patients, including sex, age, primary tumor site, clinical presentation, and previous radiation history, were summarized.
The TNM staging for each involved case referred to the American Joint Committee on Cancer (AJCC) Cancer Staging manual for head and neck cancer (8 th Edition, 2017).
The clinical outcomes for each case were collected and summarized retrospectively from the follow-up information.

Imaging examinations
All patients experienced enhanced computed tomography (CT) and/or magnetic resonance imaging (MRI) examinations from the skull base to the clavicular level at their primary visit and during follow-up. Chest CT imaging was also performed for each case at the first visit and during follow-up. Representative CT/MRI images were downloaded from the Hospital Information System (HIS) of the hospital.

Microscopic observations
The final pathological reports were presented based on pathologic examinations by

Statistical analysis
Statistical analyses were conducted using IBM SPSS Statistics version 20.0 software (IBM Corp., Armonk, NY, USA). The overall survival for the included cases was analyzed by Kaplan-Meier method. A p-value <0.05 was considered statistically significant.

Clinical characteristics of the involved UPS patients
As shown in Table 1, of the 10 involved UPS patients, 5 patients were male (median age at diagnosis 46.8 years, range 39-59 years), and 5 patients were female (median age at diagnosis 49.6 years, range 20-79 years). Regarding the primary sites of origin included the gingiva (4/10), tongue (3/10), buccal mucosa (1/10), palate (1/10), and maxillary sinus (1/10). Clinically, the most common symptom was the presentation of a rapidly and widely progressive soft-tissue mass. At the time of primary diagnosis, all patients developed tumors at the T3/T4 stage. In addition, no lymph node metastasis or distal metastasis was detected in any of the cases at their primary diagnosis. Based on the medical history of the involved patients, 2 patients had records of OSCC history with previous radiation therapy.

Imaging characteristics of the UPS in oral-maxillary area
As summarized in Table 1 and adjuvant radiotherapy/chemotherapy compared with other cases (median survival: 6.25 months, range: 5-12 months; p=0.0101; Figure 3B). Seven cases died from the recurrence of the UPS in head and neck, and 2 cases died from lung metastasis and the subsequent malignant pleural effusions ( Figure 3C-D). In addition, 1 case died from recurrence and metastasis (Table 2).

Molecular features of the UPS in oral-maxillary area
In this study, we described a rapidly progressive case of UPS originated from the buccal area (responded poorly to neoadjuvant chemotherapy and died from lung metastasis, Figure 4A) and analyzed its mutation variations ( Figure 4B). Totally, we detected 739,096 SNVS (single nucleotide variants), 113,934 INDELs (insertion or deletion), 27, 514 SVs (structure variant), and 90 gene fusions ( Figure 4B). Cancer driver genes detection revealed GBP4 as a candidate driver gene for the oral-maxillary UPS ( Figure 4C). A total of 8 missense mutations were detected in the exon 10 of the gene GPB4, including rs561042, rs561037, rs608339, rs1142890, rs1142889, rs1142888, rs1142886, and rs655260 ( Figure 4D). Besides, we also identified a missense mutation in gene PIK3CA (rs104886003, Figure 4E). The WES data revealed a high TMB (tumor mutation burden, 152.01) in the detected case ( Figure 4F). Comparatively, the MSI (microsatellite instability) rate of the case was detected as MSI-L/MSS (microsatelite instability-low/microsatelite instability-stable, Figure 4G).

Discussion
In this study, we managed to demonstrate the clinicopathological characteristics and molecular features of UPS in the oral-maxillary area for the first time. The rapidly progressive UPS can easily develop at advanced and life-threatening stage (wide invasion of soft tissues and bones), especially concerning the complex anatomical structures and spaces in the oral-maxillary area. Comparatively, regional lymph metastasis of UPS is rarely observed. The histopathological diagnosis for UPS greatly depends on the histological examination and extensive immunohistochemical markers to differentiate it from other malignant epithelial and mesenchymal tumors [4]. The main differential diagnoses that must be considered and excluded before the eventual diagnosis of UPS are poorly differentiated carcinoma, melanoma, dedifferentiated liposarcoma, pleomorphic liposarcoma, pleomorphic leiomyosarcoma, myxofibrosarcoma, pleomorphic rhabdomyosarcoma, and malignant peripheral nerve sheath tumor [6,9]. Previous studies have demonstrated that UPS is the most common histologic subtype of radiation-associated sarcoma (RAS) [10,11], and 2/10 of the included UPS patients had previous radiation-therapy history. So, radiation-induced UPS cannot be ignored for patients with radiation history in the oral-maxillary area.
Accordingly, surgical resection with negative resection margins is the mainstay of treatment for the UPS [7,9]. In our department, radical resection with negative margins has been performed for the UPS patients. Neck dissection is not regular recommended for the rare rate of cervical metastasis of UPS patients. Compared with the UPS originated from other sites, the wide tissue-defects in the oral-maxillary area greatly affect the quality of life for the patients. In our department, Simultaneous soft-tissue flaps are recommended to reconstruct the composite tissue defects of the oral-maxillary system. Besides, treatment strategies for the oral-maxillary UPS have been developing through collaboration among clinicians within a multidisciplinary team (MDT) in our department. Concerning the limited data in literature, the roles of perioperative chemotherapy and radiation have been unclear [12,13]. Herein, considering the poor prognosis of oral-maxillary UPS, MDT treatment strategy is recommended including neoadjuvant chemotherapy/targeted chemotherapy, radical surgery, adjuvant chemotherapy/targeted therapy, and adjuvant radiation.
Comparatively, the prognosis of UPS arising from oral-maxillary area is much poorer when compared with UPS in other regions [14,15]. In this study, we also observed that the cases with better responses to the neoadjuvant chemotherapy (anlotinib) had improved OS, and IHC staining also indicated the positive expression of CD31 and ERG in some cases. What's more, further investigations are definitely warranted.
Recently, the molecular characterization of UPS originated from other tissues has been demonstrated sporadically [16,17]. Activation of Hedgehog and Notch signaling pathways have been demonstrated in cells with tumor-initiating potential from UPS [6]. Besides, the VGLL3 and YAP1 in the Hippo signaling pathway have been investigated to be overexpressed in a subset of UPS [6]. However, studies on the UPS mutational landscape are rarely conducted. This study is the first to use the WES to detect the gene mutation occurring in the oral-maxillary UPS. In the detected UPS case, cancer driver genes detection revealed GBP4 as a candidate driver gene. The GBPs are the members of the guanosine triphosphatase family (GTPases) that are induced by IFNγ and have a role in resistance to pathogens [18]. A high expression of GBP1, GBP2, GBP3, GBP4 and GBP5 have been observed to be correlated to more favorable clinical outcomes in colorectal cancer, skin cutaneous melanoma, breast cancer, OSCC, esophageal squamous cell carcinoma, and Kaposi's sarcoma [19,20].
The mutations of GBP4 might play key roles in the oncogenesis of oral-maxillary UPS, and more studies are deserved to investigate the roles of mutated GBP4 in the oncogenesis of UPS in detail. Additionally, a missense mutation in gene PIK3CA (p.E545K) was also identified. Till now, the mutational activation of the PI3K pathway has been demonstrated as a central event in many types of cancer [21].
Accordingly, PIK3CA E545K cells showed increased proliferation rates in all growth conditions compared with wild-type cells [21]. So, the mutation of PIK3CA might greatly contribute to the malignant progression of the oral-maxillary UPS [22]. The WES data revealed a high TMB (tumor mutation burden, 152.01) in the detected case, which has been emerged as a promising predictive biomarker for immune checkpoint inhibitor therapy [23].
In conclusion, our findings can greatly expand the knowledge about the mutation spectrum and oncogenesis of the oral-maxillary UPS, and provide molecular evidences to improve the therapeutic options for the UPS patients. Further studies are warranted to validate our discoveries on the oral-maxillary UPS.