Acinic cell carcinoma of the salivary gland associated with lymphoid-rich stroma. A diagnostic dilemma on cytology: Study of two cases

Molecular testing in salivary gland cytopathology: A practical overview in conjunction with the Milan system

Recently, significant advances in the molecular characterization of salivary gland neoplasms have facilitated the classification and diagnosis of specific diagnostic entities. In the highly challenging diagnostic scenario of salivary malignancies, molecular testing is increasingly being adopted in routine practice to refine the cytological diagnosis of salivary lesions. Here, we reviewed the most recent evidence in the field of salivary glands molecular cytopathology.

Acinic cell carcinoma mimicking Warthin's tumor: A diagnostic challenge on fine-needle cytology

The cytologic diagnosis of acinic cell carcinoma (ACC) can be challenging due to its polymorphous appearance and sharing cytomorphologic characteristics with other benign and malignant neoplasms as well as non-neoplastic diseases, even though various histomorphological aspects of ACC have been documented. We presented a 39-year-old female patient applied with right pre-auricular parotid swelling spreading infra-auricular region which was gradually increased in size for 3 months. Ultrasonographic examination revealed hypoechoic well-circumscribed mass with 17 × 22 × 29 mm size. Magnetic resonance imaging revealed intra-parotid solid lesion with cystic areas, slightly hypointense on T1 and hyperintense on T2 weighted images. The mass was pushing the retromandibular vein medially, still lateral to it in the caudal images, but in dumbbell-shape spreading through parapharyngeal space in superiorly cranial images. Fine-needle aspiration cytology was also performed with guidance of ultrasonography. The cytological examination of the lesion was characterized by the predominance of heterogeneous lymphoid cells, clusters of epithelial cells with a variety of cytologic appearances, including granular, transparent, vacuolated, and oncocytic, and the presence of numerous naked nuclei with a protein-like foamy background. Due to intense lymphocytic inflammation, it was considered as benign primary parotid tumor such as Warthin's tumor. The excision material was examined histopathologically. Immunohistochemical analysis showed that this carcinoma was positive for DOG1, SOX10, cytokeratin 7 and negative for mammaglobin. This salivary gland tumor was reported as a rare variant of ACC with lymphoid-rich stroma. To improve the diagnostic accuracy, various morphological aspects of ACC should be considered in the pathological practice.

Morphologic and Ancillary Studies of Pediatric Acinic Cell Carcinoma: A Single Institute Experience

BACKGROUND

Acinic cell carcinoma (AciCC) is the second most common pediatric malignant salivary gland tumor. However, there are limited pathology publications about this tumor in the pediatric population.

METHODS

We describe four pediatric AciCC cases diagnosed between 2000 and 2021 in our institute. Reticulin histochemistry plus immunohistochemistry for NR4A3 and DOG1 were performed on all cases.

RESULTS

Histologically, all four cases featured a tumor-associated lymphoid proliferation and collagenous stroma, in which two formed central scars. The tumors were predominantly solid, with a lobular pattern and variably sized dilated spaces, including one case with focal microcysts. High-grade transformation was not observed in any of our cases. Reticulin stain and immunohistochemistry for NR4A3 showed distinct features between AciCC and non-neoplastic salivary gland parenchyma. DOG1 immunohistochemistry confirmed the acinar origin of AciCC.

CONCLUSIONS

Our study reveals that pediatric AciCCs often present with tumor-associated lymphoid proliferation (TALP) and sclerosis. Special stains such as reticulin histochemistry and NR4A3 immunohistochemistry are helpful to separate tumor from adjacent benign parenchyma. The ancillary study is helpful for the diagnosis of small specimens. Our study is limited by its low case number, but we hope that our results will promote more studies on this rare salivary gland tumor in the pediatric population.

Utility of NR4A3 on FNA cytology smears and liquid-based preparations of salivary gland

BACKGROUND

Fine-needle aspiration cytology (FNAC) is generally the initial sampling method for salivary gland neoplasms. The cytomorphologic features of acinic cell carcinoma (AciCC) of salivary gland can overlap with other neoplastic and nonneoplastic entities. AciCCs harbor a recurrent t(4;9) rearrangement with upregulation of nuclear receptor subfamily 4 group A member 3 (NR4A3). NR4A3 protein overexpression has been shown to be highly sensitive and specific for the diagnosis of AciCC in histologic specimens and cell block preparations. However, data on NR4A3 immunocytochemistry (ICC) on conventional smears or liquid-based cytology are limited.

METHODS

The authors identified 18 FNAC of histologically proven AciCC cases between 2013 and 2019. FNAC samples of diagnostic mimickers were likewise retrieved and included in the study cohort for comparison. The NOR1/NR4A3 mouse monoclonal antibody was applied directly to FNAC slides using a standard ICC technique.

RESULTS

The cohort included ethanol-fixed Papanicolaou-stained cytologic smears and liquid-based preparations from 18 AciCC, one secretory carcinoma, four mucoepidermoid carcinomas, four salivary duct carcinomas, five pleomorphic adenomas (PA), five Warthin tumors, five oncocytomas, one oncocytic hyperplasia, and five nonneoplastic salivary gland cases. Strong nuclear staining for NR4A3 was present in all AciCC, weak nuclear staining was present in one PA, and all other non-AciCC were negative (sensitivity, 100%; specificity, 97%).

CONCLUSIONS

NR4A3 ICC can be used directly on FNAC conventional smears and liquid-based cytology to reliably distinguish AciCC from its mimickers. This marker may be useful in cases where a cell block preparation is unavailable or inadequate.

NOR-1 (NR4A3) immunostaining on cytologic preparations for the preoperative diagnosis of acinic cell carcinoma of the salivary gland

INTRODUCTION

Acinic cell carcinoma of the salivary gland (ACC-SG) is characterized by recurrent rearrangements in the nuclear receptor subfamily 4 group A member 3 (NR4A3). Immunostaining using an antibody targeting this rearrangement, neuron-derived orphan receptor 1 (NOR-1), has been recently studied on surgical specimens and cell block material of fine-needle aspirates for the diagnosis of ACC-SG. Our goal was to evaluate whether NOR-1 immunostaining could reliably be performed on destained cytologic preparations.

MATERIALS AND METHODS

This was a retrospective multi-institutional study. Immunostaining with the NOR-1 antibody (sc-393902 [H-7], Santa Cruz Biotechnology Inc.) was performed at a titer of 1:30 on destained cytologic preparations. ACC-SG cases (n = 17) were represented by twelve cases with alcohol-fixed preparations (n = 12), including direct smears and SurePath preparations, as well as 5 cases with air-dried preparations (n = 5). These were compared to 27 mimicker lesions (n = 27): normal acini (4), chronic sialadenitis (3), oncocytoma (2), pleomorphic adenoma (6), Warthin tumor (8), mucoepidermoid carcinoma (1), secretory carcinoma (2), and salivary duct carcinoma (1).

RESULTS

The positivity of NOR-1 in ACC-SG cases was 100% on destained alcohol-fixed preparations (12/12) and 60% on air-dried preparations (3/5). All 27 mimicker lesions were negative for NOR-1 (0/27). Evaluation of 2 ACC-SG cases with both types of cytologic preparations showed that NOR-1 was positive on the alcohol-fixed slides but negative on the air-dried slides.

CONCLUSIONS

NOR-1 immunostaining can reliably be performed on alcohol-fixed direct smears and liquid-based preparations for the diagnosis of ACC-SG. Air-dried preparations show a lower positivity rate and may be less suitable for diagnostic immunostaining.

Cytopathology of acinic cell carcinoma: A study of 50 cases, including 9 with high-grade transformation

BACKGROUND

Although largely readily recognizable in tissue sections, acinic cell carcinoma (ACC) remains diagnostically problematic in fine-needle aspiration (FNA) cytopathology. The authors undertook an analysis of a large series of ACC aspirates, including acinic cell carcinoma with high-grade transformation (ACC-HGT).

METHODS

The authors searched their cytopathology files for ACC cases with histopathologic confirmation. FNA biopsy was performed according to standard techniques.

RESULTS

Fifty FNA biopsy cases of ACC (including 36 of parotid origin [72%]) from 41 patients (female to male ratio, 1.4:1; age range, 23-84 years; average, 54 years) met the study inclusion requirements. Primary neoplasm aspirates were most common (72%), and they were followed by recurrent tumors (16%) and metastases (12%). A precise cytologic diagnosis was made for 64%. Three of 9 ACC-HGT cases (33%) were correctly interpreted as such; 98% of conventional ACC cases were correctly graded as low-grade. With the Milan classification system, 74% fit into the malignant category. Ancillary testing was performed for only 36%. Conventional ACC had moderately to highly cellular smears; monotonous cells in aggregates and single forms; rounded nuclei; and microvacuolated, finely granular, oncocyte-like, or nonspecific cytoplasm. ACC-HGT smears contained larger nuclei, high nuclear to cytoplasmic ratios, coarse nuclear chromatin, and a loss of cytoplasmic granules/vacuoles.

CONCLUSIONS

A correct diagnosis of ACC via FNA biopsy was made in almost two-thirds of the cases. With the Milan classification, 84% of the cases would have been classified as malignant or suspicious for malignancy. An absence of conventional serous acinar cell morphology in some cases as well as an absence of ancillary immunohistochemistry testing in almost two-thirds of the cases prevented even better diagnostic performance.