Sclerosing Polycystic Adenosis Arising in the Parotid Gland Without PI3K Pathway Mutations

Abstract

A 15-year-old old Japanese male with a 2-month history of swelling of his left subauricular area was admitted to our department. A thumb-sized, hard mass with mild tenderness was palpated on the left parotid gland. Ultrasonography revealed a well-circumscribed, hypoechoic mass exhibiting heterogeneity in the left parotid gland measuring 1.7 × 1.5 × 1.3 cm. Computed tomography scan revealed a well-circumscribed, solid mass exhibiting slight peripheral enhancement in the left parotid gland. Magnetic resonance imaging revealed a hypointense mass in the left parotid gland on both T1- and T2-weighted images. Clinicoradiologic findings suggested a benign or low-grade malignant parotid tumor. The patient underwent left superficial parotidectomy with adequate safety margins. The facial nerve was identified and preserved. Neither facial paralysis nor tumor recurrence was observed as of 1 year postoperatively. Histologically, the nodule consisted of a vaguely nodular arrangement of variably sized ducts and acini in a hyalinized fibrous background with focal myxoid changes. The ductal/acinar component exhibited a bilayered arrangement of cuboidal luminal and flattened abluminal cells exhibiting a variety of epithelial proliferative patterns, including micropapillary and cribriform. Areas of oncocyte-like changes with intracellular coarse eosinophilic granules, apocrine-like feature, foamy/vacuolated changes, and clear cells were noted in the proliferating epithelium. Immunohistologically, the luminal cells were positive for gross cystic disease fluid protein-15. The Ki-67 labeling index was 2–3%. The histologic features and immunohistologic profile were consistent with sclerosing polycystic adenosis. Targeted next-generation sequencing of 160 cancer-related genes using the surgical specimen revealed no mutations, including known significant mutations in PTEN, PIK3CA, or PIK3R1.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12105-021-01339-z.

Introduction

Sclerosing polycystic adenosis (SPA), a rare benign lesion arising in salivary glands, histologically resembles low-grade ductal carcinoma in situ or sclerosing adenosis of the breast [1]. SPA was first reported in 1996 as a rare salivary gland pseudoneoplastic condition [2]. In the 2017 fourth update of the World Health Organization (WHO) classification of tumours of the salivary glands [1], SPA was categorized as a non-neoplastic epithelial lesion. Since 2006, only 38 cases of SPA arising in the parotid gland have been reported [3–20]. Because of its rarity, neither the etiology nor the clinical features of SPA have been fully elucidated.

Case Report

A 15-year-old old Japanese male with a 2-month history of swelling of his left subauricular area was admitted to our department. A thumb-sized, hard mass with mild tenderness was palpated on the left parotid gland. No facial palsy was observed. Ultrasonography revealed a well-circumscribed, hypoechoic mass exhibiting heterogeneity in the left parotid gland measuring 1.7 × 1.5 × 1.3 cm (Fig. 1a). Computed tomography (CT) scan revealed a well-circumscribed, solid mass exhibiting slight peripheral enhancement in the left parotid gland (Fig. 1b). Magnetic resonance imaging (MRI) revealed a hypointense mass in the left parotid gland on both T1- and T2-weighted images (WIs) (Fig. 1c-f). Fine-needle aspiration cytology (FNAC) was performed, but the specimen was unsatisfactory for evaluation due to marked hypocellularity. Clinicoradiologic findings suggested a benign or low-grade malignant parotid tumor. The patient underwent left superficial parotidectomy with adequate safety margins. The facial nerve was identified and preserved. Neither facial paralysis nor tumor recurrence was observed as of 1 year postoperatively.

Fig. 1.

Imaging findings of the tumor. Ultrasonography revealed a well-circumscribed, hypoechoic mass exhibiting heterogeneity in the left parotid gland, measuring 1.7 × 1.5 × 1.3 cm (a). Computed tomography scan revealed a well-circumscribed, solid mass exhibiting slight peripheral enhancement in the left parotid gland (b). Magnetic resonance imaging revealed a hypointense mass in the left parotid gland on both T1- and T2-weighted images in axial (c, d) and coronal sections (e, f). The tumor is indicated by arrowhead

The specimen was serially sectioned, revealing a well-circumscribed, slightly lobulated, tan-white, homogeneous nodule (Fig. 2a). Histologically, the nodule consisted of a vaguely nodular arrangement of variably sized ducts and acini in a hyalinized fibrous background with focal myxoid changes (Fig. 2b). The ductal/acinar component revealed a bilayered arrangement of cuboidal luminal and flattened abluminal cells exhibiting a variety of epithelial proliferative patterns, including micropapillary (Fig. 2c) and cribriform (Fig. 2d), similar to intraductal hyperplasia of the breast. The proliferating epithelium also exhibited areas of oncocyte-like changes with intracellular coarse eosinophilic granules (Fig. 2e), apocrine-like features (Fig. 2f), foamy/vacuolated changes, and clear cells. Few mitotic figures were identified in the ductal epithelium, whereas cytologic atypia was mild.

Fig. 2.

Histologic findings of the tumor. The specimen appeared as a well-circumscribed, slightly lobulated, tan-white, homogeneous nodule (a). Histologically, the nodule consisted of a vaguely nodular arrangement of variably sized ducts and acini in a hyalinized fibrous background with focal myxoid changes (b). The ductal/acinar component revealed a bilayered arrangement of cuboidal luminal and flattened abluminal cells exhibiting a variety of epithelial proliferative patterns, including micropapillary (c) and cribriform (d), similar to intraductal hyperplasia of the breast. The proliferating epithelium also demonstrated areas of oncocyte-like changes with intracellular coarse eosinophilic granules (e), apocrine-like features (f), foamy/vacuolated changes, and clear cells. Immunohistologically, luminal cells were positive for gross cystic disease fluid protein-15 (g). Abluminal cells were myoepithelial and reactive for α- smooth muscle actin (h). The Ki-67 labeling index was 2–3% (i). Scale bars: 100 μm

Immunoperoxidase staining of formalin-fixed, paraffin-embedded tissue sections with specific antibodies (Abs) was performed using a Ventana OptiView DAB IHC Detection kit (Roche Diagnostics, Basel, Switzerland) on an automated Ventana BenchMark XT platform (Roche). The following Abs were used: (a) anti–gross cystic disease fluid protein (GCDFP)-15 monoclonal antibody (mAb) (clone 23A3, dilution 1:50; Agilent, Santa Clara, CA); (b) anti–α-smooth muscle actin (SMA) mAb (clone 1A4, dilution 1:100; Agilent); and (c) anti–Ki-67 mAb (clone MIB1, no dilution; Agilent). Luminal cells were positive for GCDFP-15 (Fig. 2g). Androgen receptor was also positive (data not shown). No immunoreactivity against human epidermal growth factor receptor(HER)-2, p53, or S-100 protein was observed (data not shown). In contrast, abluminal cells were myoepithelial and reactive for α-SMA (Fig. 2h). The Ki-67 labeling index was 2–3% (Fig. 2i). Fluorescence in situ hybridization (FISH) was performed as described elsewhere [21] and revealed absent split signals of the ETS translocation variant 6 (ETV6) gene in tumor-cell nuclei. The histologic features, immunohistologic profile, and FISH results were consistent with a SPA of the parotid gland. Genetic analysis was performed as previously described [22]. Briefly, total DNA was extracted from 5-μm-thick formalin-fixed paraffin-embedded tissue sections of the tumor and peripheral blood samples. A GeneRead DNA seq Targeted Panel V2 human comprehensive cancer panel (NGHS-501X; Qiagen, Valencia, CA) was used for amplicon sequencing of targeted regions of 160 cancer-related genes (Table S1). Libraries were sequenced using a MiSeq (Illumina, San Diego, CA). Raw read data obtained from the amplicon sequencing were processed using online analytical resources from the GeneRead DNAseq Variant Calling Service for analysis of mutations. No mutations, including known significant mutations in genes such as PTEN, PIK3CA, or PIK3R1, were identified.

Discussion

SPA affects the parotid gland in approximately 70% of cases, with occasional cases affecting the submandibular glands or oral cavity [2, 3, 23, 24]. Since 2006, only 38 cases of SPA affecting the parotid gland including the present case have been reported (Table S2) [3–20]. SPA can occur in persons across a wide age range (7–84 years), with a median age of 46 years, and slight female predominance among reported cases (23 females, 15 males). The maximal diameter of lesions ranges from 1.2 to 11.8 cm. Clinically, lesions typically present as a slow-growing, rounded, palpable, elastic-to-hard mass in the parotid area, with or without pain or tenderness.

Unfortunately, published imaging findings of parotid SPA are limited given its rarity. Ultrasonographically, SPA tumors have been described as well-circumscribed, hypoechoic masses with microcystic areas [7, 20]. On CT scan, the lesions have been described as well-circumscribed, hypodense masses exhibiting peripheral enhancement [15, 17]. In MRI studies, several findings have been described, including a parotid mass with small cystic areas of diffuse hypointensity on T1-WIs and slight hyperintensity on T2-WIs [12, 19], but contradictory findings (i.e., hypointensity on T2-WIs) have also been reported [9, 17]. These inconsistent T2-WI findings could be explained by the relative areas of small cystic and hyalinized sclerotic components within SPA tumors. The present case exhibited a hypointense mass on both T1- and T2-Wis. This enabled preoperative differentiation from a pleomorphic adenoma, which is characterized by hyperintensity on T2-WIs.

Diagnosing SPA by FNAC is challenging given the varying cytologic features [6–8, 19, 24]. No cases in previous reports were diagnosed as SPA, but 5 of 14 cases were instead preoperatively diagnosed as pleomorphic adenoma (Table S2). Described cytologic features of SPA include syncytial epithelial ductal cells with focal apocrine changes, oncocytes, and a cystic-type background with foamy macrophages and proteinaceous material [23]. The presence of different cell types within a given single sheet, including small ductal, apocrine, and sebaceous-like cells with finely vacuolated cytoplasm, is a key cytologic diagnostic feature of SPA [7]. Histologically, SPA appears as a sharply circumscribed, mostly unencapsulated lesion composed of acinar and ductal components with variable cytomorphologic characteristics, including foamy, vacuolated, apocrine, mucous, clear/ballooned, squamous, columnar, and oncocyte-like cells [23]. Another characteristic of SPA is the presence of large acinar cells with abundant eosinophilic cytoplasmic granules. The stroma is densely collagenized and frequently harbors a variably intense chronic inflammatory infiltrate. Immunohistologically, focal positivity for GCDFP-15, a general marker of apocrine differentiation, can be noted, particularly in the cytoplasm of apocrine-like cells [19]. Both ductal and acinar cells are positive for broad-spectrum cytokeratins, but immunoreactivity against epithelial membrane antigen is variable. HER-2, p53, and S-100 protein are reportedly negative [25]. The Ki-67 proliferative index is low (1–2%) in the acinar and ductal components. Histologic differential diagnosis of SPA includes intraductal carcinoma (IDC), also known as low-grade salivary duct carcinoma (SDC)/low-grade cribriform cystadenocarcinoma, and mammary analogue secretory carcinoma (MASC) of the parotid gland. IDC tumors tend to exhibit more complex cystic patterns and lack epithelial cells with a foamy/vacuolated or clear cytoplasm along with intracytoplasmic eosinophilic granules. SPA can be extinguished from MASC by the absence of the ETV6-neurotrophic receptor tyrosine kinase (NTRK) 3 fusion gene, which is observed in 90% of MASC cases [25].

A single study examining polymorphisms of the human androgen receptor (HUMARA) in 6 cases of SPA reported X-chromosome inactivation in all 6 cases, indicating that SPA is a clonal, neoplastic process [4]. Another study using targeted NGS reported that 4 of 4 SPA cases exhibited alterations in genes including PTEN, PIKCA and PIK3R1 in the phosphatidylinositol-3 kinase (PI3K) pathway [26]. Genetic alterations in the PI3K pathway have been identified in a variety of human tumors, including SDC and an apocrine variant of IDC [27]. The authors suggested that SPA is a neoplasm and should therefore more correctly be named ‘sclerosing polycystic adenoma’. In the present case, contradictory results were obtained in that no mutations in PTEN, PIKCA, or PIK3R1 were identified via NGS using a targeted amplicon-based NGS panel that covered all exons of the three genes. If we consider SPA as a neoplasm, mutations in genes other than the 160 analyzed using the DNA-based platform could be related to the neoplastic process of SPA. As we had not performed an analysis of X-chromosome inactivation, we could not determine whether the SPA mass in the present case was a neoplasm or non-neoplastic epithelial lesion. Further study will therefore be needed.

All patients described in previous reports were treated with various excisional procedures, including enucleation, and partial, superficial, and total parotidectomy (Table S2). In previous reports, 3 of 30 patients (10%) with parotid SPA experienced tumor recurrence [3, 13, 14]. These recurrences were attributed to incomplete excision of the lesion. The outcome of SPA after complete resection is reportedly favorable, with no reports of metastasis or lethality. Regarding malignant transformation, one patient developed an invasive carcinoma arising from recurrent SPA 33 years after the first excision [14].

Conclusion

We report a rare case of parotid SPA in an adolescent. No recurrence was observed 1 year after superficial parotidectomy. No mutation in genes of the PI3K pathway were identified using NGS.

Supplementary Information

Below is the link to the electronic supplementary material.

Authors’ Contributions

AU, NB, TG, RS, SS, and AK conducted the surgery and provided bedside care. AU and NB drafted the manuscript. TY, HN and HT performed pathologic investigations. SB and YK performed mutational analyses. YH conceived the study design. All authors approved the final version of the manuscript.

Funding

This study received no funding from any sources.

Declarations

Conflict of interest

The authors declare that there are no actual or potential conflicts of interest in relation to this article.

Ethical Approval

All procedures performed on patient tumor samples in this study were in accordance with the ethical standards of the Institute Ethics Committee and the 1964 Helsinki declaration and its later amendments or comparable ethical standards.

Informed consent

Written informed consent for publication of clinical details and images was obtained from the patient and his family.