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 Table of Contents  
Year : 2021  |  Volume : 8  |  Issue : 3  |  Page : 213-216

A rare malignant transformation in pleomorphic adenoma

1 Department of Pathology, ABVIMS and RML Hospital, New Delhi, India
2 Department of Surgery and Transplant, ABVIMS and RML Hospital, New Delhi, India
3 Department of Surgery, ABVIMS and RML Hospital, New Delhi, India

Date of Submission13-Jun-2021
Date of Decision28-Jun-2021
Date of Acceptance29-Jun-2021
Date of Web Publication23-Aug-2021

Correspondence Address:
Shivani Kundal
Department of Pathology, Room No. 323, 3rd Floor, ABVIMS and Dr. RML Hospital, New Delhi - 110 001
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jdrr.jdrr_104_21

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Carcinoma ex pleomorphic adenoma (Ca ex PA) is a rare type of malignant salivary gland tumor. Myoepithelial carcinoma (MEC) as the malignant component in Ca ex PA is an even rarer occurrence. Preoperative pathological diagnosis of Ca ex PA often goes unnoticed in many cases as they may be clinically indolent and the malignant component may not be picked up on fine-needle aspiration cytology. However, features such as rapid growth, recurrent tumor, and pain point toward a malignant transformation. We present a case of a 40-year-old female who presented with a history of recurrent swelling over parotid region with cytological diagnosis of pleomorphic adenoma, which on excision was reported as Ca ex PA with MEC being the malignant constituent. Till date, few cases of MEC arising from PA have been reported. It presents as a diagnostic challenge to both clinicians and pathologists alike; prognosis is still not clear due to few number of cases and lack of follow-up in most of them.

Keywords: Facial nerve, myoepithelioma, parotid gland, recurrence, salivary gland neoplasms

How to cite this article:
Misra S, Mudgal P, Kundal S, Ahuja A, Agarwal N, Kansakar N. A rare malignant transformation in pleomorphic adenoma. J Dent Res Rev 2021;8:213-6

How to cite this URL:
Misra S, Mudgal P, Kundal S, Ahuja A, Agarwal N, Kansakar N. A rare malignant transformation in pleomorphic adenoma. J Dent Res Rev [serial online] 2021 [cited 2021 Nov 27];8:213-6. Available from: https://www.jdrr.org/text.asp?2021/8/3/213/324409

  Introduction Top

Carcinoma ex pleomorphic adenoma (Ca ex PA) represents malignant transformation of a pre-existing pleomorphic adenoma, usually in long-standing pleomorphic adenoma or in tumor with multiple recurrences. It usually presents as a diagnostic challenge to clinicians as it may be asymptomatic and invasive component is likely to be missed on fine-needle aspiration cytology (FNAC). Adenocarcinoma not otherwise specified (NOS) is the most common morphologic subtype to develop in Ca ex PA followed by adenoid cystic carcinoma, mucoepidermoid carcinoma, or salivary duct carcinoma.[1] Myoepithelial carcinoma (MEC) is one of the rarest malignancies of salivary gland and constitutes only about 0.1%–0.45% of all salivary gland tumors.[2] MEC origin may be de novo or may arise from preexisting benign lesions including pleomorphic adenoma and benign myoepithelioma.[3] MEC as the malignant component in Ca ex PA is extremely rare.[1] Myoepithelial differentiation with infiltration and destructive growth into surrounding tissues are features of MEC. Parotid gland is the most frequently involved salivary gland in MEC. Submandibular gland and other minor salivary glands are less frequently involved.[3] Patients with high-grade invasive Ca ex PA have worse prognosis than minimally invasive counterparts.[4] We present a rare case of Ca ex PA; invasive MEC arising from parotid gland in a patient who came with a diagnosis of pleomorphic adenoma on FNAC.

  Case Report Top

A 40-year-old lady presented with recurrent swelling over infra-auricular region of the right side of the face for 1 year. Patient had undergone surgery twice elsewhere few years back, reports of which were not available. On examination swelling was non tender, slightly mobile and firm in consistency; FNAC performed was reported as pleomorphic adenoma. On contrast-enhanced computed tomography, a large 4.4 cm × 3.4 cm irregular heterogeneous enhancing mass lesion was noted in right buccal space. Lesion was abutting right masseter muscle medially and superior aspect of right anterior parotid gland posteriorly [Figure 1]. Patient underwent total parotidectomy (facial nerve sparing) with supraomohyoid dissection and specimen was sent for histopathological examination.
Figure 1: Axial contrast-enhanced computed tomography image showing lobulated heterogeneously enhancing mass lesion in the right parotid region (yellow arrow) abutting right masseter muscle medially and superior aspect of right anterior parotid gland posteriorly

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Grossly, two circumscribed partially encapsulated nodular gray-white firm areas were noted in the superficial lobe of parotid gland. Cut surface of deep lobe of parotid gland also showed focal gray-white areas. Both lesions were reaching up to the dermis of the overlying skin flap. Microscopically, multiple sections taken from superficial parotid lobe on low power magnification (×40) showed a partly circumscribed tumor arranged in the form of varying sized lobules separated by fibrous septa [Figure 2]a. High power magnification (×200) shows tumor cells arranged in sheets, cords, and trabeculae. Individual tumor cells were polygonal in shape with enlarged nuclei, vesicular chromatin, and prominent nucleoli and had moderate-to-abundant eosinophilic to vacuolated cytoplasm [Figure 2]b. Areas of myxoid change were also noted. In addition, pleomorphic adenoma component was also identified within an occasional tumor nodule composed of cords and compressed tubular units of myoepithelial, epithelial cells embedded in abundant chondromyxoid stroma (H and E, ×40) [Figure 2]c. Deep parotid lobe also revealed involvement by tumor with similar morphology. Tumor was focally seen reaching up to deeper dermis microscopically at low power magnification (×40) [Figure 2]d; however, no epidermal ulceration was noted. Seven reactive lymph nodes were isolated.
Figure 2: (a) Low power photomicrograph shows variably sized nodules of tumor separated by fibrous septae (H and E, ×40); (b) high power photomicrograph shows tumor cells arranged in trabeculae and nests and are polygonal with enlarged nuclei, vesicular chromatin, prominent nucleoli and have moderate-to-abundant eosinophilic to vacuolated cytoplasm (H and E, ×200); (c) low power photomicrograph shows a tumor nodule with pleomorphic adenoma component (H and E, ×40); (d) low power photomicrograph shows tumor nodule in the deep dermis (long arrow), adnexal structures are marked with red arrow (H and E, ×40)

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Immunohistochemical analysis at intermediate power magnification (×100) shows tumor cells strong positivity for vimentin [Figure 3]a, S100 [Figure 3]b, SMA [Figure 3]c, and EMA. Patchy positivity [Figure 3d] was seen for Pan-CK and CD117. CD10 and CEA both were negative. Based on history of recurrent swelling, extent of invasion, and histological and immunohistochemical findings, final diagnosis of Ca ex PA, invasive MEC (stage pT4A N0 Mx) was given. Patient was referred for radiotherapy and is well at 6-month postsurgery.
Figure 3: (a-c) High power photomicrographs show tumor cells diffusely positive for vimentin, S100 and SMA (IHC, ×100); (d) tumor cells show patchy positivity for Pan-CK (IHC, ×100)

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  Discussion Top

Ca ex PA constitutes approximately 3.6% of all salivary gland neoplasms and 11.6% of all malignant salivary gland neoplasms.[1] In the natural course of PA, malignant transformation occurs in approximately 1.6%–7.5% cases of PA. In most cases of Ca ex PA, females outnumber males. It typically occurs during 6th to 8th decade of life and most commonly involves parotid gland, followed by submandibular gland. Other rare sites of involvement include breast, lacrimal glands, nasal cavities, and trachea.[5] Most patients present clinically as firm to hard swelling of the parotid gland. Other features of malignancy include fixation of swelling to skin or underlying tissues, facial nerve palsy, pain, and restricted mobility.[1],[3]

The exact pathogenesis of Ca ex PA is still not clear. Role of genetic instability, increased expression of p16 protein in cytoplasm of cells, and radiation have been postulated in various studies.[6] Adenocarcinoma NOS is the most common morphologic subtype to develop in Ca ex PA. Other common subtypes include salivary duct carcinoma, adenoid cystic carcinoma, and mucoepidermoid carcinoma. In contrast, acinic cell carcinoma, epithelial-MEC, basal cell carcinoma, MEC, squamous cell carcinoma, and clear cell carcinoma are rarely encountered histologic subtypes in Ca ex PA.[1] Our case is unique as it occurred at a younger age (40 years) and the malignant subtype was invasive MEC.

MEC is a rare tumor; therefore, clinical features, pathophysiology, and management of MEC are not well characterized.[7] There is no sex predilection seen in MEC and age of presentation in most cases is around 55 years.[8] Preoperative diagnosis of MEC ex PA on FNAC is not possible in most of the cases as FNAC is only 29%–54% sensitive in making preoperative diagnosis of high-grade salivary gland tumors.[2]

Grossly, MEC of parotid gland is usually encapsulated, while at other locations, it is unencapsulated.[3] In our case, the recurrent parotid tumor was invasive, focally reaching the dermis and also involving the deep lobe of parotid. Microscopically, tumor cells are arranged in the different patterns such as in the form of multiple nodules, solid sheets, and reticular or trabecular pattern and are separated by variable amounts of fibrovascular septa. Areas of myxoid change or hyalinization can also be seen. Tumor cell morphologically can be plasmacytoid, hyaline type, spindle shaped, stellate, epithelioid, or clear cell type. Metaplastic changes in the form of chondroid, squamoid, or sebaceous differentiation can also be seen in MEC.[3] In our case, cells were arranged in sheets, trabeculae, and cords; predominant cell population was of epithelioid cell type with focal clear cells. Katabi et al.,[9] in a large series of over a 27-year period, identified 15 cases of MEC ex PA. We have highlighted the previously reported cases of MEC ex PA in [Table 1].
Table 1: Characteristics of previously reported cases of myoepithelial carcinoma ex-pleomorphic adenoma (myoepithelial carcinoma ex pleomorphic adenoma)

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Tumors with clear cells, epitheloid, plamacytoid, and spindle cell morphology come under differential diagnosis of MEC.[8] One of the myoepithelial markers and cytokeratin positivity is essential for making diagnosis of MEC.[3] In our case, tumor cells were strongly positive for vimentin, S100, SMA, and EMA and showed patchy positivity for Pan CK which confirmed the diagnosis of MEC, Ca ex PA.

MEC/Ca ex PA may be widely invasive and aggressive with a tendency to recur or even metastasize. MECs are seen to metastasize to distant sites more frequently than the involvement of regional lymph nodes. Lungs are the most common site of metastasis.[3],[8] MEC arising from pleomorphic adenoma has worse prognosis compared to de novo MEC.[8] Ablative surgery is the treatment of choice for Ca ex PA, which in some patients are followed by reconstructive surgery.[20] Radiotherapy is often used postoperatively in metastatic tumors, but the role of chemotherapy is still not clear.[8] After histopathology diagnosis, our case was referred for radiotherapy and is doing well 6-month postsurgery.

  Conclusion Top

Ca ex PA is a difficult diagnosis to make as there is substantial overlap in histopathological features; however, certain clinical clues such as detailed history, presence of preexisting pleomorphic adenoma at the same location, radiological features, and panel of immunohistochemical stains can help in making an accurate diagnosis of Ca ex PA. The correct diagnosis would be helpful in guiding patient management and treatment protocols for improving the survival rates in these rare malignancies.

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.

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Conflicts of interest

There are no conflicts of interest.

  References Top

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Gupta A, Manipadam MT, Michael R. Myoepithelial carcinoma arising in recurrent pleomorphic adenoma in maxillary sinus. J Oral Maxillofac Pathol 2013;17:427-30.  Back to cited text no. 3
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  [Figure 1], [Figure 2], [Figure 3]

  [Table 1]


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