Polymorphous adenocarcinoma of the parotid – An uncommon site of occurrence

Prabhat Mahato; Chhanda Das; Ankita Pranab Mandal; Madhumita Mukhopadhyay

doi:10.4103/ijamr.ijamr_207_21

CASE REPORT

Year : 2022 | Volume : 9 | Issue : 1 | Page : 52-54

Polymorphous adenocarcinoma of the parotid – An uncommon site of occurrence

Prabhat Mahato, Chhanda Das, Ankita Pranab Mandal, Madhumita Mukhopadhyay
Department of Pathology, Institute of Post Graduate Medical Education and Research, Kolkata, West Bengal, India

Date of Submission	24-Sep-2021
Date of Decision	22-Jan-2022
Date of Acceptance	23-Jan-2022
Date of Web Publication	30-Mar-2022

Correspondence Address:
Dr. Ankita Pranab Mandal
Flat No. B501, Gulmohar II CHS Ltd, Plot No. 13, Sector-42, Seawood, Nerul - 400 706, Navi Mumbai, Maharashtra
India

Source of Support: None, Conflict of Interest: None

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DOI: 10.4103/ijamr.ijamr_207_21

Abstract

Polymorphous low-grade adenocarcinoma is a neoplasm of the minor salivary glands and is malignant in origin but is indolent in nature. Currently, this neoplasm is documented and known as polymorphous adenocarcinoma (PAC) by WHO Classification of Salivary Gland Tumors (2017). Of all the salivary neoplasms, minor salivary gland neoplasm accounts for 9%–23%. Very rarely, it involves major salivary glands such as parotid, submandibular, and sublingual in <5% cases. It may develop either de novo or from pleomorphic adenoma. PAC mimics some benign as well as malignant neoplasms. Histopathological features alone cannot diagnose PAC due to the overlapping features with other neoplasms, and so immunohistochemistry is essential to confirm the diagnosis and hence aids in the proper management of PAC. We report a case of PAC arising from parotid gland in a 52-year-old male treated with facial nerve preservation.

Keywords: Immunohistochemistry, parotid, polymorphous adenocarcinoma, salivary gland

How to cite this article:
Mahato P, Das C, Mandal AP, Mukhopadhyay M. Polymorphous adenocarcinoma of the parotid – An uncommon site of occurrence. Int J Adv Med Health Res 2022;9:52-4

How to cite this URL:
Mahato P, Das C, Mandal AP, Mukhopadhyay M. Polymorphous adenocarcinoma of the parotid – An uncommon site of occurrence. Int J Adv Med Health Res [serial online] 2022 [cited 2023 Mar 25];9:52-4. Available from: https://www.ijamhrjournal.org/text.asp?2022/9/1/52/341341

Introduction

Polymorphous low-grade adenocarcinoma (PLGA) is a neoplasm of the minor salivary glands and is malignant in origin but is indolent in nature.^[1] Of all the salivary neoplasms, minor salivary gland neoplasm accounts for 9%–23%.^[2] In 1983, PLGA was first labeled as terminal duct carcinoma by Batsakis et al. and lobular carcinoma by Freedman et al. Currently, this neoplasm is documented and known as polymorphous adenocarcinoma (PAC) by WHO Classification of Salivary Gland Tumors (2017).^[1],[3],[4] Wide limited local excision is the choice of treatment for PLGA.^{[3],[5],[6],[7],[8],[9]} We report a case of PAC arising from parotid gland which was treated with facial nerve preservation.

Case Report

A 52-year-old male presented with right preauricular painless swelling, progressively increased in size for a period of 5 years. On clinical examination, swelling was firm and nontender. He underwent contrast-enhanced computed tomography of face and neck which revealed a well-defined cystic lesion with few thick enhancing septa and solid irregular mural nodules in the superficial lobe of right parotid gland [Figure 1]a. Magnetic resonance imaging showed 7 cm × 5 cm × 5 cm heterogeneously enhancing solid cystic hyperintense altered signal intensity lesion in superficial lobe of right parotid gland, obliterated fat planes with masseter muscles and ramus of mandible, extending superiorly up to preauricular region. Fine-needle aspiration was performed from the swelling, and the cytomorphological features were suggestive of a cystic lesion of the salivary gland, having atypia of undetermined significance, Milan category III.

Figure 1: (a) Computerized tomography scan shows large well-defined SOL (b) Gross specimen (c) Section shows tumor mass arranged in tubular and papillary pattern (×100, H and E) (d) Section shows atypical tumor cells with pleomorphic vesicular nuclei, prominent nucleoli and nuclear grooving (×400, H and E)

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The lesion was surgically excised through right superficial parotidectomy with facial nerve preservation. Grossly, the lesion was well-circumscribed measuring 6 cm × 5 cm × 4 cm. On cut open, whitish homogenous area was noted with cystic spaces in between [Figure 1]b. Histologically, the section showed tumor mass composed of neoplastic cells arranged in branching tubular and somewhere in papillary pattern [Figure 1]c. Lining cells were highly atypical with pleomorphic vesicular nuclei and prominent nucleoli [Figure 1]d. Nuclear grooving was noted. Intraluminally, eosinophilic secretions were also seen. Neither perineural invasion nor vascular invasion was seen. Lymphoid aggregates and hemorrhages were also seen. The histopathological features were consistent with PAC. The eosinophilic secretions were periodic acid–Schiff positive. Immunohistochemical examination was performed by peroxidase-antiperoxidase technique using cluster of differentiation (CD) 117 (monoclonal mouse antibody; clone: EP10, positive control: testis, and cytoplasmic/membranous staining), cytokeratin 7 (CK7) (monoclonal mouse antibody; clone: OVTL12/30, positive control: lung, and cytoplasmic/membranous staining), p63 (monoclonal mouse antibody, clone: 4A4, positive control: specimen of prostate; and nuclear staining), and S100 (polyclonal rabbit antibody; clone: 15E2E2, positive control: melanoma, and cytoplasmic staining). Tumor cells showed strong and diffuse positivity to S100 [Figure 2]a. Tumor cells also showed positivity to CK7, p63, and CD117 [Figure 2]b, [Figure 2]c, [Figure 2]d. These immunohistochemical findings confirmed the diagnosis of PAC which differentiates it from pleomorphic adenoma and adenoid cystic carcinoma.

Figure 2: (a) Immunohistochemistry staining for S100 showing positivity (×400) (b) Immunohistochemistry staining for CK7 showing positivity (×400) (c) Immunohistochemistry staining for p63 showing positivity (×400) (d) Immunohistochemistry staining for CD117 showing positivity (×400)

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Discussion

Salivary gland tumors are very unusual. Of all the head-and-neck neoplasms, it comprises 2%–6.5% affecting mainly major salivary glands, particularly the parotids.^[10] PAC is a distinct neoplasm illustrated by architectural variety, cytological regularity, and clinically painless and slow-growing. Mucoepidermoid carcinoma is the most common minor salivary gland malignancy followed by PAC.

Palate (49%–77.8%) is the most common site of origin of PAC, followed by buccal mucosa or upper lip (7.4%–13.4%).^{[11],[12],[13]} It may also involve the tongue, floor of the mouth, alveolar ridge, and lower lip. Very rarely, it involves major salivary glands such as parotid, submandibular, and sublingual in <5% cases. Furthermore, it is also seen in other sites like breast, vagina, lung.^[14],[15] PAC is mainly seen in adult patients from 3^rd to 7^th decades with a highest incidence from 5^th to 6^th decades of life. It occurs most commonly in females than in males.^[11] Some reports have suggested that it arises de novo or as neoplasms developing in a preexistent pleomorphic (carcinoma ex pleomorphic adenoma).^[16],[17] In this report, PAC developed de novo in the parotid gland. Surgical excision either superficial or deep parotidectomy is the treatment of choice. Macroscopically, it is well-circumscribed, nonencapsulated, and firm. Microscopically, architectural patterns are solid, trabecular, glandular, spindled, fascicular, ductal, and cystic. Tumor cells are cuboidal to columnar with eosinophilic cytoplasm and enlarged nucleoli with mucoid to hyaline stroma.^[18]

Immunohistochemical staining aids in the diagnosis of PAC, as tumor cells stain positive with S100, Epithelial membrane antigen (EMA), and CK7. p63 also stains positive.^[19],[18] In this report, PAC showed positivity to CD117, CK7, p63, and S100. Pleomorphic adenoma, monomorphic adenoma, and adenoid cystic carcinoma share the histologic characteristics as PAC, so they are considered the differential diagnosis. Lack of infiltration is seen in pleomorphic adenoma and monomorphic adenoma and pleomorphic adenoma presents with chondromyxoid matrix so they can be distinguished from PAC but they have the propensity for perineural invasion. Pleomorphic adenoma stains are positive for glial fibrillary acidic protein, but PAC is negative. Adenoid cystic carcinoma shows histologic patterns such as cribriform, tubular and solid, and exhibit basaloid cells with scant cytoplasm, PAC illustrates some spindling. PAC shows strong diffuse positivity S100 and EMA while adenoid cystic carcinoma stains much less diffusely. Low-grade papillary adenocarcinoma (LGPA) is also considered a differential for PAC. However, LGPA demonstrates a more aggressive behavior, and the rate of local recurrence and regional lymph node metastasis are higher.^[20],[21]

PAC is associated with PRKD1 mutations and adenoid cystic carcinoma shows MYB or MYBL1 gene rearrangements.^[22] These genetic abnormalities are pathognomonic of the tumors and can also be useful in the differential diagnosis. We were not able to perform genetic studies because of financial constraints. PAC sometimes erodes the underlying bone and may even show perivascular or perineural invasion. Metastases are very rare and even if present is mostly restricted to the regional lymph nodes.^[23]

Wide limited local excision is the choice of treatment approach.^[6] If tumor is seen at surgical margin, then postoperative radiotherapy is suggested. Adjuvant radiotherapy and radical surgical excision are recommended in cases of cervical metastases. In recurrent cases, radical surgery is done.^{[5],[6],[7],[8]} In this case report, no metastasis was identified and was treated surgically with facial nerve preservation that is superficial parotidectomy.

Conclusion

PAC is a tumor of minor salivary gland but it may also arise in the major salivary gland which may develop either de novo or from pleomorphic adenoma. PAC has an indolent behavior and may mimic a benign neoplasm, so a thorough examination of the entire surgical specimen should be done. Histopathological features alone cannot diagnose PAC due to the overlapping features with other neoplasms, and so immunohistochemistry is essential to confirm the diagnosis and hence aids in the proper management of PAC.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient (s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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