[Patient-derived parotid gland pleomorphic adenoma organoid model and its preliminary histological and functional characterization].

Objective: To establish patient-derived organoid models of pleomorphic adenomas (PA) of the parotid gland and preliminarily characterize their histology, related biomarkers and functions. Methods: Fresh tumor tissue specimens were collected from surgical procedures of Oral and Maxillofacial Department. The harvested tissues were processed and cultured in a head and neck tumor organoid culture system to establish organoid models from parotid gland pleomorphic adenomas. The in vitro growth of PA organoids was recorded by light microscopy. The successfully established organoids were passaged and cryopreserved, and the cryopreserved PA organoids were revived and re-cultured to observe their viability and organoid regeneration ability. Histological characterization, as well as characterization and detection of related markers and functional proteins, were performed on the organoids, comparing them with the patient-derived tissues. Results: The constructed organoid model of pleomorphic adenoma exhibited a dense and compact three-dimensional spherical structure. Hematoxylin and eosin staining indicated morphological similarities between the organoid and its tissue of origin. Immunohistochemistry showed positive cytoplasmic staining for Calponin, cytokeratin 7, and epithelial membrane antigen in both the organoid and the source tumor tissue, suggesting consistent histopathological characteristics between the organoid and its tissue of origin. Periodic acid-Schiff staining of the organoid showed positive staining for glycogen, with positive staining located in the interior and periphery of the organoid, indicating that the organoid possessed secretory functions like the salivary gland. Conclusions: This study successfully constructed organoids of pleomorphic adenoma derived from patient samples. This model faithfully replicates the tissue morphology and biomarkers of the source tissue and exhibits biological functions associated with mucus secretion. It serves as a valuable in vitro model for studying the development and progression of salivary gland tumors.

Expression of Periostin in Benign Salivary Gland Tumors.

Parotid tumors present a wide range of histological features, from benign to malignant. Periostin, an extracellular matrix protein specifically expressed in the periosteum and periodontal ligament, is isolated from osteoblast cell lines. It regulates fibrosis and collagen deposition and plays an important role in myocardial repair after myocardial infarction. It is also known to be involved in otorhinolaryngological-diseases. This study included 36 patients [38 specimens; 16 men and 20 women, mean age 59.2 (range 26-82) years] who underwent parotid tumor resection at the Division of Otorhinolaryngology, Tohoku Medical and Pharmaceutical University, between April 2017 and March 2022 and were clinically and pathologically diagnosed as having benign parotid tumors. Formalin-fixed, paraffin-embedded sections from the surgical specimens were autoclaved and immunostained with anti-periostin antibodies to evaluate the expression and distribution of periostin. Histologically, the tumors were diagnosed as pleomorphic adenomas in 15 cases (15 specimens), Warthin's tumors in 13 cases (15 specimens), basal cell adenomas in 2 cases (2 specimens), oncocytomas in 4 cases (4 specimens), and myoepitheliomas in 2 cases (2 specimens). An increased expression of periostin was found in 32 of 38 samples (84.2%) in the stroma of benign parotid tumors. Four distinct patterns of periostin expression were observed in benign parotid gland tumors: negative, superficial, infiltrative, and diffuse. Statistically significant differences were found between periostin expression patterns and histological classification of the tumors. Our results suggest that periostin may be involved in the pathogenesis of benign parotid tumors and could serve as a new biomarker for these tumors.

Hybrid Carcinoma of the Parotid Gland: An Extremely Rare Three Cases with an Immunohistochemical Analysis and a Review of the Literature.

Salivary hybrid carcinoma (HC) is defined as when two or more kinds of carcinoma exist at the same location in a single mass. We reestimated and examined three cases of salivary gland HC. Case 1 involved a 76-year-old male. Case 2 involved a 74-year-old female. Case 3 involved a 66-year-old male. Histologically, case 1 involved a combination of salivary duct carcinoma (SDC) and squamous cell carcinoma (SqCC). Immunohistochemically, the former was positive for gross cystic disease fluid protein (GCDFP)-15 and androgen receptor (AR). Case 2 involved a combination of SqCC and neuroendocrine carcinoma. Immunohistochemically the latter was positive for synaptophysin and neural cell adhesion molecule (NCAM). Case 3 involved a combination of SDC and epithelial-myoepithelial carcinoma (EMC). Immunohistochemically, the former was positive for GCDFP-15 and AR, whereas the inner cells of the latter were positive for cytokeratin 7, and the outer cells of the latter were positive for actin. Because of the transitional zone between SDC and EMC, it was speculated that high-grade SDC arose from low-grade EMC.

Imaging Features and Pathological Analysis of 43 Parotid Basal Cell Adenomas.

PURPOSE: To investigate the correlation between sonographic and computed tomography and pathological features of basal cell adenomas (BCAs) of the parotid gland. METHODS: This retrospective study included 41 patients (43 tumors) with BCAs. The tumors were divided into three types based on their location in the parotid gland and their imaging features. The features of the tumors were analyzed. RESULTS: Imaging manifestations and corresponding pathological results of most BCAs of the parotid glands resembled those of benign parotid gland tumors. Malignant transformation occurred in membranous BCAs and in those with extensive cribriform structures. Type-II and type-III tumors accounted for 82.93% of the total proportion. Thirteen tumors showed cystic degeneration with 30.23%, among which type-III tumors could easily develop cystic degeneration. These cystic areas might correspond to cystic degeneration or focal necrosis. Cystic change was not dependent on the tumor size. The pathological features of the tumors were correlated to their imaging manifestations. CONCLUSION: Most BCAs of the parotid glands have imaging manifestations similar to those of benign parotid gland tumors. BCAs with extensive cribriform structures and of the membranous type can show malignant transformation and should be treated with caution in clinical practice.

Increase in Chymase-Positive Mast Cells in Recurrent Pleomorphic Adenoma and Carcinoma Ex Pleomorphic Adenoma of the Parotid Gland.

Incomplete excision of pleomorphic adenoma (PA) may result in recurrent pleomorphic adenoma (RPA). Furthermore, long-term neglected PA may become carcinoma ex pleomorphic adenoma (CXPA). In the present study, the relationships between mast cell-derived chymase and these tumors were examined. The tumor tissues of PA consisted of either or both glandular and fibrotic structures. Histological features of RPA were almost similar to those of PA, except that they showed multinodular structures. CXPA is composed of a mixture of PA and carcinoma. The main stromal cells in PA were myofibroblasts, whereas fibroblasts constituted the main cellular portion in the stromal tissue of RPA. Cancer-associated fibroblasts (CAFs) were present abundantly in CXPA. With increased VEGF expression, neovascularization tended to increase in RPA or CXPA. Compared with PA, chymase-positive mast cells, as well as chymase gene expression, were increased in the tumor tissues from patients with RPA or CXPA. SCF, TGFß1, and PCNA-positive staining was widely observed in these tumor tissues. The above results suggest that mast cell-derived chymase through its direct or cooperative effects with other mediators may participate in the pathophysiology of RPA and CXPA.

Short communication: Distribution of phospholipids in parotid cancer by matrix-assisted laser desorption/ionization imaging mass spectrometry.

BACKGROUND: Parotid cancer is relatively rare, and malignancy varies; therefore, novel markers are needed to predict prognosis. Recent advances in matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI-IMS), useful for visualization of lipid molecules, have revealed the relationship between cancer and lipid metabolism, indicating the potential of lipids as biomarkers. However, the distribution and importance of phospholipids in parotid cancer remain unclear. OBJECTIVE: This study aimed to use MALDI-IMS to comprehensively investigate the spatial distribution of phospholipids characteristically expressed in human parotid cancer tissues. METHODS: Tissue samples were surgically collected from two patients with parotid cancer (acinic cell carcinoma and mucoepidermoid carcinoma). Frozen sections of the samples were assessed using MALDI-IMS in both positive and negative ion modes, with an m/z range of 600-1000. The mass spectra obtained in the tumor and non-tumor regions were compared and analyzed. Ion images corresponding to the peak characteristics of the tumor regions were visualized. RESULTS: Several candidate phospholipids with significantly different expression levels were detected between the tumor and non-tumor regions. The number of unique lipid peaks with significantly different intensities between the tumor and non-tumor regions was 95 and 85 for Cases 1 and 2, respectively, in positive ion mode, and 99 and 97 for Cases 1 and 2, respectively, in negative ion mode. Imaging differentiated the characteristics that phospholipids were heterogeneously distributed in the tumor regions. CONCLUSION: Phospholipid candidates that are characteristically expressed in human parotid cancer tissues were found, demonstrating the localization of their expression. These findings are notable for further investigation of alterations in lipid metabolism of parotid cancer and may have potential for the development of phospholipids as biomarkers.

A case of "ETV6-FISH-negative" secretory carcinoma of the parotid gland: immunohistochemical study.

Secretory carcinoma of the salivary glands is a relatively new disease concept, and is characterized by "morphological resemblance to mammary secretory carcinoma and ETV6-NTRK3 gene fusion." Herein we describe a confusing case and briefly discuss practical diagnostic problems. The patient was a 71-year-old Japanese man who had a tumor consistent with secretory carcinoma at the microscopic and immunohistochemical levels. Immunohistochemically, EMA and S100 protein were noted to be positive along with various cytokeratins as well as mammaglobin and pSTAT5. Moreover, vimentin was focally positive. Smooth muscle actin, p63, p40, and androgen receptor were negative. However, a search using fluorescence in situ hybridization did not reveal a definite split signal for the ETV6 gene. It is presumed that confirming the diagnosis of secretory carcinoma without genetic retrieval will be accepted as a diagnostic method, and we hope that worldwide general recognition may earlier reach "gradual acceptance."

Warthin Tumor Incidentally Detected on PET/CT Showing Both 68Ga-DOTANOC and 18F-FDG Uptake.

ABSTRACT: A patient with moderately differentiated pancreatic neuroendocrine tumor with synchronous multifocal liver metastases was referred for further staging with PET/CT. The examinations were performed on 2 consecutive days and showed mild 68Ga-DOTANOC and intense 18F-FDG uptake in an incidental right parotid nodule. Differential diagnoses include primary or metastatic neuroendocrine tumor, malignant or benign primary parotid tumor, and intraparotid lymph node. Histology revealed characteristics of a Warthin tumor. While focal FDG uptake in Warthin tumor is frequently described, the somatostatin expression was rarely reported. This clinical case describes 68Ga-DOTANOC and 18F-FDG uptake in a parotid Warthin tumor histologically confirmed.

Diagnostic Value of Superb Microvascular Imaging in Parotid Tumors.

BACKGROUND The aim of this study was to evaluate the clinical diagnostic value of superb microvascular imaging (SMI) in assessing vascular distribution, vascularity, and vessel morphology of parotid tumors (PTs). MATERIAL AND METHODS PT patients confirmed by postoperative histopathological detection and who underwent color Doppler flow imaging (CDFI), microvascular imaging (MVI), and SMI examination were recruited. PTs were classified into 3 groups: pleomorphic adenoma (PA), Warthin tumor (WT), and malignant PT (MT). The tumor vascular distribution, vascularity, and vessel morphology recorded by CDFI, MVI, and SMI were compared among PA, WT, and MT group. PT diagnosis was performed using histopathological detection. Fisher's exact test was used to compare the diagnostic sensitivity, specificity, negative predictive value (NPV), positive predictive value (PPV), and accuracy between SMI and MVI examination in PTs. RESULTS We enrolled 198 PTs consisting of 114 PAs, 56 WTs, and 28 MTs into our study. CDFI examination found no significant differences in vascular distribution and vascularity among the PA, WT, and WT groups. SMI examination found significant differences in vascular distribution and vascularity among the 3 groups. MVI found significant differences in vessel morphology, including uneven distribution of blood flow, arborization, and irregular blood flow among the PA, WT, and MT groups. SMI found significant differences in arborization and irregular blood flow, but none of the differences in uneven distribution of blood flow among the 3 groups were significant. The diagnostic sensitivity, specificity, and accuracy of SMI and MVI in PTs showed no significant differences. CONCLUSIONS SMI more accurately evaluated the vascular distribution and vascularity of PTs than CDFI. SMI might be a potential non-invasive diagnostic method for PTs in clinical practice.

Rare Epididymal-Derived Myoepithelial Carcinoma: A Case Report and Review of Literature.

Myoepithelial carcinoma (MC), also known as malignant myoepithelial neoplasm, is more common in the parotid glands of the head and neck. The main clinical manifestation is the growth of a nonspecific, painless mass at the primary site. We report the first case of MC derived from the epididymis. The current reports of non-parotid MC are still rare, and epididymal-derived MC has not been reported previously. Simultaneously, we explore the role of EWSR1 fusion as a predicting marker and further reveal the origin of MC to provide new ideas for its diagnosis and treatment.

Ectopic ACTH Secretion Secondary to Metastatic Acinic Cell Carcinoma of the Parotid Gland: A Case Report and Review of Current Evidence for Systemic Therapy.

Acinic cell carcinoma is a rare, typically indolent, neoplasm that arises in the salivary glands. Metastatic disease is uncommon, occurring in around 10% of cases. We report the case of a 46-year-old male in whom the first sign of disseminated disease was increased skin pigmentation due to paraneoplastic Cushing's syndrome. He underwent 3 cycles of chemotherapy with carboplatin and paclitaxel with no symptomatic improvement and a mixed response on imaging. There is no evidence that systemic therapy prolongs survival in metastatic acinic cell carcinoma, and we lack a consensus as to which treatment options are most beneficial. A summary of published evidence regarding choice of palliative chemotherapy regimens and response is discussed in relation to the case.

HDAC Overexpression in a NUT Midline Carcinoma of the Parotid Gland with Exceptional Survival: A Case Report.

NUT midline carcinoma (NMC) is a recently described entity with a predilection for young individuals, characterised by a rearrangement of NUT, most commonly with BRD4. It usually involves midline structures, with a minority of cases presenting outside the midline axis. Given its dismal prognosis, new molecularly targeted therapies (eg, HDAC inhibitors) are gaining ground, but the HDAC expression pattern remains unknown. We describe the exceptional evolution of a NMC arising in the parotid gland. A 34-year-old male presented with a rapidly growing 35 mm left-parotid mass. Parotidectomy and lymphadenectomy were performed. The tumour invaded the surrounding soft tissue and lay adjacent to the surgical margin. No lymph node metastases were identified. Histology revealed blue nests of undifferentiated cells merging with foci of necrosis and occasional abrupt foci of keratinising squamous epithelium. FISH analysis confirmed a rearrangement of NUT, but not of BRD4. A diagnosis of NMC was rendered. Currently, after adjuvant chemoradiotherapy and 47 months after diagnosis, the patient is alive and well. The tumour was found to have increased immunoexpression of HDAC2, 4 and 6 and phospho-HDAC4/5/7. This case emphasises the importance of considering NMC in the differential diagnosis of poorly differentiated carcinomas of the head and neck region in young adults, even away from midline structures. As molecular targets hold the promise of successful therapy for the vast majority of NMC patients, the knowledge of their HDAC expression patterns will probably be relevant.

Programmed death ligand-1 expression is associated with stage and histological grade of parotid carcinoma.

Background: The immune checkpoint ligand programmed death ligand-1 (PD-L1) is expressed by various cancers, including those of the head and neck. However, the role of PD-L1 is still unknown.Objectives: To investigate the relationship between PD-L1 expression and survival rate in parotid carcinoma.Methods: PD-L1 expression was investigated by immunohistochemical analysis in 127 patients with parotid carcinoma. The relationship between PD-L1 expression and stage, histological grade, and survival was assessed.Results: PD-L1 expression was found in 28.3% of parotid carcinomas, with the expression being higher in tumors with a higher stage, a higher-grade, and node positive cases. However, the 5-year disease-specific survival rate was 82.2% for the patients with PD-L1 positive and 86.9% for those with PD-L1 negative tumors, showing no significant difference.Conclusions: PD-L1 expression was positive in approximately 50% of high- grade carcinomas, which was similar to the level in head and neck squamous cell carcinoma. In patients with other cancers, it has been reported that an anti-PD-1 monoclonal antibody was more effective against tumors with higher PD-L1 expression. Therefore, it could be a possible new therapeutic option for patients with highly malignant parotid tumors that have a poor prognosis.

Ectopic ACTH Production and Cushing's Syndrome in a Patient with Parotid Acinic Cell Carcinoma with High-Grade Transformation: Tumor Context and Clinical Implications.

We report a rare case of Cushing's syndrome in a 59-year-old man who initially presented with concurrent acinic cell carcinoma of the parotid with high-grade transformation and co-existing papillary and medullary thyroid carcinomas, without noticeable cushinoid symptoms. Six-months later, he developed clinical features of Cushing's syndrome which coincided with disease progression in the form of lung metastasis and mediastinal lymphadenopathy. Ectopic adrenocorticotropic hormone (ACTH) production and protein expression was limited to the high-grade transformed component of acinic cell carcinoma and in the lymph node metastasis, and was absent in the conventional acinic cell carcinoma as well as in the papillary and medullary thyroid carcinoma. He received adjuvant chemotherapy and supportive management with interval improvement for 8 months followed by disease progression with increasing serum cortisol levels and bone metastasis. He was offered palliative chemotherapy, however, declined further therapy and was lost to follow up. We discussed clinical and pathologic implications of ectopic ACTH production associated with acinic carcinoma and also reviewed the literature of this rare paraneoplastic syndrome.

A Distinctive Genomic and Immunohistochemical Profile for NOTCH3 and PDGFRB in Myofibroma With Diagnostic and Therapeutic Implications.

Introduction. Myofibromas are rare tumors of pericytic lineage, typically affecting children, and are sometimes aggressive. A subset of sporadic and familial myofibromas have activating variants in PDGFRB. The relationship of myofibroma and PDGFRB to the NOTCH pathway has not yet been described. Methods. Ten myofibroma cases were sequenced with a targeted panel of 447 genes, including copy number variation and selected fusions. Immunohistochemical analysis of total NOTCH3 and activated NOTCH3 was assessed for all 10 myofibroma cases, and a series of histologic mimics (n = 20). Results. Alterations identified by next-generation sequencing included PDGFRB sequence variants in 8/10 cases (80%), a NOTCH3 variant in 1/10 cases (10%), and a NOTCH2 variant in 1/10 cases (10%). All 10 cases also showed a pattern of low-amplitude (1.5- to 2-fold) copy number alterations including gains in PDGFRB and NOTCH3. Ten of 10 myofibromas (100%) showed cytoplasmic staining for total NOTCH3 and 9 of 10 cases (90%) showed nuclear staining for activated NOTCH3. Within the control cohort of histologic mimics, 3 of 3 nodular fasciitis cases (100%) were positive for activated and total NOTCH3, and the remaining 17 cases were negative for pan NOTCH3, while 3 of 3 desmoid-type fibromatosis cases (100%) showed patchy weak nuclear staining for activated NOTCH3. Discussion. Our findings suggest a common pathway of PDGFRB/NOTCH3 activation in myofibromas, even in cases that lack PDGFRB sequence variants. These results support the pericytic lineage of myofibroma. Identification of the characteristic genomic alterations or immunohistochemical staining pattern may facilitate a difficult pathologic diagnosis, and support the use of targeted treatments.

Expresión de Ki67 y MUC-1 en el adenocarcinoma no especificado de otra manera (NOS) de glándulas salivales: su valor pronóstico / Ki67 and MUC-1 expression in adenocarcinoma not otherwise specified (NOS) of salivary glands: prognostic value

El adenocarcinoma NOS (no especificado de otra manera) es un tumor salival sin patrón especial poco mencionado en la literatura; su diagnóstico es un desafío porque estructuralmente no se identifica con otros carcinomas salivales más definidos. Por otro lado, Ki67 es un marcador de proliferación celular que brinda información pronóstica de las neoplasias. En cuanto a la mucina humana transmembrana MUC-1 se sobre-expresa en las neoplasias malignas perdiendo su localización exclusivamente apical. Presentamos dos casos de adenocarcinoma NOS diagnosticados con H/E y correlacionamos la expresión de Ki67 y la localización y sobreexpresión de MUC-1 con su grado histológico y pronóstico. Cortes histológicos de dos adenocarcinomas NOS de parótida en mujeres de 62 y 63 años respectivamente se colorearon con H/E e inmunomarcaron para Ki67 y MUC-1. En ambos tumores predominaban estructuras ductales, algunas quísticas, cordones celulares ramificados e islotes sólidos. Las formaciones glandulares presentaban células claras y algunas de aspecto oncocítico. Había importante atipia celular, comedonecrosis, invasión perineural, áreas hemorrágicas y compromiso de los márgenes quirúrgicos. La marcación nuclear con Ki67 fue importante; MUC-1 presentó una fuerte coloración en membranas y citoplasmas. Las dos lesiones se diagnosticaron como de alto grado de malignidad. Nuestros resultados demuestran que existe una importante proliferación marcada con Ki67 y una sobre-expresión de MUC-1 asociadas a atipia celular, infiltración perineural, necrosis y compromiso de márgenes quirúrgicos, factores asociados a un peor pronóstico. El reconocimiento de este tumor es trascendente para médicos y odontólogos ya que por la ausencia de rasgos distintivos que sí presentan otros carcinomas más específicos es fundamental el diagnóstico de exclusión.

Adenocarcinoma NOS (not otherwise specified) is a no special pattern salivary tumor briefly mentioned in the literature; its diagnosis is a challenge because structurally it is not identified with other more definite salivary carcinomas. On the other hand, Ki67 is a marker of cellular proliferation that provides prognostic information of neoplasms. As for human transmembrane mucin, MUC-1 is overexpressed in malignant neoplasms, losing their exclusively apical location. We present two cases of adenocarcinoma NOS diagnosed with H/E and correlate the expression of Ki67 and the location and over-expression of MUC-1 with its histological grade and prognosis. Histological sections of two NOS adenocarcinomas of parotid in women of 62 and 63 ages respectively were stained with H/E and immunolabelled for Ki67 and MUC-1. Both are predominated by ductal structures, some cystic, branched cell cords and solid islets. The glandular formations presented clear cells and some of oncocytic appearance. There was important cellular atypia, comedonecrosis, perineural growth, haemorrhagic areas and compromise of surgical margins. Nuclear marking with Ki67 was important; MUC-1 presented a strong staining in membranes and cytoplasms. They were diagnosed as high-grade malignancy. Our results show that there is an important proliferation marked with Ki67 and overexpression of MUC-1 associated with cellular atypia, perineural growth, necrosis and compromise of surgical margins, factorsassociated with a poor prognosis. The recognition of this tumor is transcendent for physicians and dentists since, due to the absence of distinctive features that other more specific carcinomas present, the diagnosis of exclusion is essential.

Clinical characteristics of acinic cell carcinoma and secretory carcinoma of the parotid gland.

PURPOSE: Mammary analogue secretory carcinoma (SC) of the parotid gland is a relatively uncommon cancer associated with the ETV6-NTRK3 fusion product similar to breast cancer. The clinical characteristics and outcome of treatment were reviewed for patients with this tumor at our hospital. METHODS: In this retrospective case series, 24 patients with a diagnosis of acinic cell carcinoma (AcCC) of the parotid gland were classified as having either SC or AcCC based on analysis of the ETV6-NTRK3 fusion gene. These two groups were compared with respect to their clinical and imaging characteristics (MRI/US), cytologic findings, accuracy of fine-needle aspiration cytology and frozen section, treatment outcomes, and immunohistochemical findings. RESULTS: Based on re-classification by ETV6-NTRK3 fusion gene analysis, the diagnosis was SC in 14 patients and AcCC in 10 patients. The SC group had a significantly higher proportion of male patients and was also significantly younger than the AcCC group. Imaging studies revealed that SC was significantly more likely to show internal heterogeneity. Correct grading of both tumors was comparable by fine needle aspiration, with the rate being 60% for AcCC and 50% for SC. Diagnosis by frozen section biopsy diagnosis obtained the correct grade in 90% of the AcCC group and 93% of the SC group. CONCLUSIONS: In 24 patients previously diagnosed with AcCC, re-analysis of the ETV6-NTRK3 fusion product indicated that 14 patients actually had SC. Although AcCC and SC show similarities of their biological aggressiveness and prognosis, patients with SC were significantly more likely to be male and younger.

Radionuclide Therapy With 177Lu-PSMA in a Case of Metastatic Adenoid Cystic Carcinoma of the Parotid.

In vivo prostate-specific membrane antigen (PSMA) overexpression creates an opportunity for PSMA-directed theranostic approach in adenoid cystic carcinoma of the parotid. Herein, we illustrate a patient with metastatic PSMA-directed theranostic approach in adenoid cystic carcinoma of the parotid who had intense PSMA uptake on metastatic lesions, followed by radionuclide therapy with Lu-PSMA.

Hyaluronic acid induced foreign body reaction mimicking neoplastic parotid cytology.

Masses near the angle of the mandible containing extracellular matrix or mucin on cytology raise concern for various benign and malignant parotid gland neoplasms. Here a 76-year-old female with a history of cosmetic hyaluronic acid (HA) filler injections presented with a painless 6 mm left sided facial mass. Injection of hyaluronidase into the mass had failed to cause regression, raising concern for a neoplastic process. Fine-needle aspiration (FNA) showed amorphous, mucinous/extracellular matrix-like material in a background of numerous histiocytes and occasional multinucleated giant cells, consistent with a foreign body giant cell reaction to HA. This uncommon reaction to HA filler creates previously unrecognized diagnostic pitfalls because of its resemblance on FNA to the extracellular matrix or mucin found in many salivary neoplasms.