|Year : 2011 | Volume
| Issue : 1 | Page : 84-87
Polymorphous low-grade adenocarcinoma of the parotid gland
Arvind Krishnamurthy1, Anitha Vaidhyanathan1, Urmila Majhi2
1 Department of Surgical Oncology, Cancer Institute (WIA), 36, Sardar Patel Road, Adyar, Chennai-600 020, India
2 Department of Pathology, Cancer Institute (WIA), 36, Sardar Patel Road, Adyar, Chennai-600 020, India
|Date of Web Publication||5-May-2011|
Department of Surgical Oncology, Cancer Institute (WIA), 36, Sardar Patel Road, Adyar, Chennai - 600 020
Polymorphous low-grade adenocarcinoma (PLGA) has been recently recognized as a distinct entity with a known predilection for minor salivary glands. We present an unusual case of recurrent PLGA arising within the right parotid gland in a 25-year-old lady. The striking histological picture is diverse architecture combined with benign cytological features. Even in the light of multiple recurrences, our tumor displayed a relatively indolent course which is commonly associated with this adenocarcinoma sub-type. Thus, unusual occurrence demonstrates that this tumor should also be considered in differentials of tumors of the major salivary glands. Long-term follow-up is essential to ensure local control.
Keywords: Parotid gland, polymorphous low-grade adenocarcinoma, salivary neoplasm
|How to cite this article:|
Krishnamurthy A, Vaidhyanathan A, Majhi U. Polymorphous low-grade adenocarcinoma of the parotid gland. J Can Res Ther 2011;7:84-7
| > Introduction|| |
Polymorphous low-grade adenocarcinoma (PLGA) is a well-recognized entity within minor salivary glands and has a distinctive clinical and histological picture. The true incidence of PLGA of the parotid gland is not known as many previous reports suggest low-grade salivary duct carcinomas of the parotid to be erroneously diagnosed as PLGA. We report a true case of PLGA originating from the parotid gland and discuss the challenges in its diagnosis and management of this rare entity.
| > Case Report|| |
A 25-year-old lady presented initially in 2005 with what was believed to be her third recurrence of a right parotid tumor since its initial onset in 1993. On evaluation, we found a large painless right parotid tumor of about 10 × 9 cm. The facial nerve was intact and there was no significant neck adenopathy. She reported recurrences within a year of all previous surgeries; the last was seven years prior; she however did not have the pertinent records for our confirmation.
She was counseled for evaluation and a possible surgery, but was soon lost for follow-up only to present four years later in December 2009 with pain and fungation from the right parotid tumor which had gradually progressed over the years to attain a size of about 15 × 10 cm [Figure 1]a, b. The facial nerve functions continued to be preserved; there was still no significant neck adenopathy.
|Figure 1: (a) Preoperative clinical photograph of the patient, (b) Postoperative clinical photograph of the patient|
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Consenting for surgery this time, she was further evaluated; a punch biopsy from the ulcerated parotid tumor was suggestive of an epithelial neoplasm. A computed tomography scan of the parotid was done to delineate the extent of the tumor, it was found to involve both the superficial and deep lobes of the parotid and was seen extending up to the parapharyngeal space. The tumor was also seen infiltrating the overlying skin and soft tissues, the masseter, and upper portion of sternocleidomastoid; however, the underlying mandible was free [Figure 2]a, b. She was taken up for surgery and underwent wide excision of the tumor; the facial nerve was sacrificed as it was seen coursing through the tumor and could not be dissected free from the tumor. The resultant defect was covered by means of an anterolateral thigh microvascular free flap; a tarsorrhaphy for the right eye was done in the same sitting ([Figure 3]a, b show intraoperative picture after removal and the radical parotidectomy specimen). The final histology revealed a 15 × 11 × 6-cm multinodular tumor; microscopic analysis revealed a tumor with extensive fibrosis and calcification. The cells were seen in acinar formations of varying sizes, lined by cuboidal epithelial cells with scanty cytoplasm. The nuclei were found to be round to oval and vesicular, some of them showed oncocytic changes. The lobules of glandular structure were seen to be separated by fibrous strands. Cystic papillary formations and necrosis were not seen, the mitotic activity was low. The final impression was that of a PLGA [Figure 4]a, b.
|Figure 2: (a) Axial CT scan images showing tumor extent, (b) Coronal CT scan images showing tumor extent|
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|Figure 3: (a) Intraoperative photograph following removal of the parotid tumor, (b) Radical parotidectomy specimen|
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|Figure 4: (a, b) H and E × 40- characteristic histological picture of PLGA|
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Postoperative external beam radiotherapy of 56 Gy was given in view of it being a large T4a recurrent tumor. She is asymptomatic and is on regular follow-up for close to a year now.
| > Discussion|| |
The term "polymorphous low-grade adenocarcinoma" was initially described by Evans and Batsakis  to describe a cytologically bland but architecturally diverse malignant neoplasm of minor salivary gland origin that had been previously recognized as lobular carcinoma, terminal duct carcinoma, and low-grade papillary adenocarcinoma. Since its description, the terminology of PLGA has been widely accepted as it describes well the special features of this carcinoma: varied histologic pattern, cytologic uniformity, infiltrating growth, and a very low tendency for aggressive behavior. 
Commonly described in the minor salivary glands, it has been less commonly reported in the major salivary glands. There have been isolated reports of PLGA described in the lacrimal gland, oral tongue, oropharynx, sinonasal region, and in the nasopharynx. 
There appears to be a female preponderance in the incidence of PLGA, with a reported female : male ratio from 2 : 1.  The age at presentation typically peaks in the sixth and seventh decade of life.
PLGAs usually presents as a slow-growing enlargement of the affected gland, these tumors usually do not usually metastasize.  However, some reports have testified to the fact that this entity can behave aggressively when it presents early in life, especially during adolescence.  Our patient initially diagnosed in adolescence continued to have a fairly indolent course.
In a review of all published cases by Vincent et al.,  regional metastases were reported in 9% of patients. This is more likely to occur in recurrent tumors rather than at primary presentation.
Recognition of the histopathological features of PLGA remains the major determinate in rendering an accurate diagnosis as fine-needle cytology cannot distinguish between PLGA, adenoid cystic carcinoma, and pleomorphic adenoma. Hence, PLGAs of the parotid are usually diagnosed postoperatively after excision of a lump in the gland. Various immunohistochemical markers have also been found to be positive, such as vimentin, cytokeratin, S-100, CEA, SMA, and GFAP. Markers such as Ki67 have been known to show variability in positivity. 
As in cases of other salivary gland malignancies, surgery with free margins remains the treatment of choice. The experience with adjuvant radiotherapy is limited. A few series have noted recurrences despite its use and hence have suggested that adjuvant radiotherapy has a little bearing on the prognosis. 
Recurrences have been reported in up to a third of the cases, despite being an indolent tumor. Vincent et al. found a recurrence rate of 17% with a regional metastasis rate of 9%.  Many of the recurrences have been reported after five years  ; hence, a long-term follow-up is recommended. Salvage of local recurrences in PLGA is a worthwhile pursuit as long-term disease controls are still achieved in a majority of the cases. 
Castle et al. showed an average time to recurrence of 7.2 years. With an average follow-up of 115 months, they reported a disease-specific survival of 98.2% and a local control rate of 97.6% in their series of 164 patients.
Therefore, in conclusion, the diagnosis and management of PLGA continues to be challenging; surgery with negative margins both in the primary as well as in the recurrent setting is the recommended treatment of choice; the role of adjuvant radiotherapy remains unclear.
| > References|| |
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|5.||Castle JT, Thompson LD, Frommelt RA, Wenig BM, Kessler HP. Polymorphous low grade adenocarcinoma: A clinicopathologic study of 164 cases. Cancer 1999;86:207-19. |
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]