|Year : 2015 | Volume
| Issue : 4 | Page : 1023
A rare occurrence of basal cell adenoma of palate: A case report with comprehensive immunohistochemical analysis
Surinder Pal Singh Sodhi1, Ramandeep Singh Brar1, Harkanwal Preet Singh2, Tajinder Kaur2, Rohan Dhawan1
1 Department of Oral and Maxillofacial Surgery, Dasmesh Institute of Research and Dental Sciences, Faridkot, Punjab, India
2 Department of Oral Pathology and Microbiology, Dasmesh Institute of Research and Dental Sciences, Faridkot, Punjab, India
|Date of Web Publication||15-Feb-2016|
Harkanwal Preet Singh
405 GGS, Nagar Majitha Road, Amritsar - 143 001, Punjab
Source of Support: None, Conflict of Interest: None
Basal cell adenoma (BCA) of the salivary glands is an uncommon type of monomorphic adenoma which constitutes 1% of all salivary gland tumors. It most commonly involves parotid gland, while it rarely occurs in minor salivary glands. Upper lip, buccal mucosa, and lower lip are the common intraoral sites; whereas, palate being the rarest one. Due to prognostic implications, differential diagnosis with basal cell adenocarcinoma, basaloid squamous cell carcinoma, and adenoid cystic carcinoma (AdCC) is mandatory. Considering the rarity of this lesion and histologic paradox regarding its diagnosis, we report a case of BCA of palate with emphasis on need of comprehensive immunohistochemical (IHC) analysis.
Keywords: Basal cell adenoma, immunohistochemistry, monomorphic adenoma, palate
|How to cite this article:|
Sodhi SP, Brar RS, Singh HP, Kaur T, Dhawan R. A rare occurrence of basal cell adenoma of palate: A case report with comprehensive immunohistochemical analysis. J Can Res Ther 2015;11:1023
|How to cite this URL:|
Sodhi SP, Brar RS, Singh HP, Kaur T, Dhawan R. A rare occurrence of basal cell adenoma of palate: A case report with comprehensive immunohistochemical analysis. J Can Res Ther [serial online] 2015 [cited 2017 Dec 11];11:1023. Available from: http://www.cancerjournal.net/text.asp?2015/11/4/1023/147391
| > Introduction|| |
Salivary gland tumors are relatively uncommon lesions affecting predominantly major salivary glands, especially the parotids. Tumors of minor salivary gland account for 9-23% of all salivary gland tumors.  It is estimated that minor salivary gland tumors represent 0.5-1.5% of all the head and neck admissions. 
Basal cell adenoma (BCA) is one of the rare minor salivary gland tumor classified under benign salivary gland adenomas in the Second Edition of the Salivary Gland Tumours Classification of the World Health Organization (WHO) and accounts for approximately 1.8% of all salivary gland epithelial tumors. In 1967, Kleinsasser and Klein introduced the term "basal cell adenoma" to describe a benign salivary gland tumor comprised of uniform-appearing basaloid cells arranged in solid, trabecular, tubular, and membranous patterns; but lacking the myxoid and chondroid mesenchymal-like component as seen in pleomorphic adenoma.
The majority of monomorphic adenomas shows a nonaggressive behavior and are adequately treated with soft tissue palatal excision. ,
Morphological variability, together with the relative rarity of a number of minor salivary gland tumors, can sometimes make diagnosis difficult, despite the abundance of named tumor entities.  Unfortunately, the morphological variability of these tumors is mirrored by the immunocytochemical profiles which further complicate the diagnosis. Considering the rarity of this lesion and histologic paradox regarding its diagnosis, we report a case of BCA of palate with emphasis on comprehensive IHC analysis.
| > Case report|| |
A 25-year-old male patient was referred to the Department of Oral and Maxillofacial Surgery with the chief complaint of painless swelling with respect to left side of palate since 6 months. Swelling was insidious in onset, it started initially as a small intraoral mass and gradually progressed to present size of 3 × 4 cm in largest extent with history of repeated ulcerations.
Clinical examination revealed no extraoral swelling and lymphadenopathy. Intraoral examination revealed a soft movable submucous mass on the left side of the palate extending anterioposteriorly from distal 25 to distal of 28 and mediolaterally from the free gingival margins to 1 cm short of midline [Figure 1]. Overlying mucosa was ulcerated but showed no secondary changes. Palpation confirmed the inspectory findings. The swelling was soft, non-fluctuant and nontender with no evidence of paresthesia. A provisional diagnosis of adenoma of minor salivary gland of palate was made.
|Figure 1: Soft tissue palatal mass extending anterioposteriorly from distal 25 to distal of 28 and mediolaterally from the free gingival margins to 1 cm short of midline|
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Radiological examination including panoramic and occlusal view revealed no abnormality. Computed tomography scan did not reveal any underlying bone resorption and mass was localized without any invasion into surrounding anatomical cavities.
On aspiration, negative pressure was observed suggestive of solid lesion. An incisional biopsy was performed and subjected for histopathological examination. Hematoxylin and eosin stained tissue sections showed encapsulated tumor mass composed of sheets of large and small basaloid cells with nuclear staining varying from pale to hyperchromatic. Cells were arranged in numerous strands and cords in solid and tubular pattern which were separated from each other by hyalinized connective tissue stroma. These features were suggestive of BCA [Figure 2]a].
|Figure 2: Photomicrograph showing: (a) Sheets of large and small basaloid cells arranged separated by hyalinized connective tissue stroma, (H and E stain, ×4) and inset showing high power view (×40) of basaloid cells. (b) Intense positive immunostaining for pan-CK, (c) intense positive immunostaining for CK 56, (d) moderately positive immunostaining for calponin, (e) moderately positive immunostaining for S100, (f) focal immunostaining for p63, (g) focal immunostaining for Ki 67, (h) negative immunostaining for SMA, and (i) negative immunostaining for CD117. CK=Cytokeratin, SMA=Smooth muscle actin|
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The tumor was subsequently excised under general anesthesia with 1 cm margins along with overlying palatal mucosa and resected tissue specimen was submitted for histopathological examination. To reconfirm our diagnosis, tissue-sections were further subjected to immunohistochemical (IHC) analysis using panel of markers. Pan-cytokeratin (pan-CK), CK 5/6, and S100 showed positive immunoreactivity; Calponin and p63 showed focal staining, whereas CD 117 and smooth muscle actin (SMA) showed negative staining [Table 1]. These findings reconfirmed our definitive diagnosis of BCA [Figure 2]. The wound was allowed to heal by secondary intention and the patient had an uneventful recovery and is under regular follow-up since 6 months.
| > Discussion|| |
BCA is a rare benign salivary gland neoplasm characterized by the basaloid appearance of the tumor cells and absence of the myxochondroid stromal component as seen in pleomorphic adenoma. ,
Previously, BCA was once considered to be a type of monomorphic adenoma, but Salivary Gland Tumours Histological Classification by World Health Organization (1991) renamed it as BCA, excluding the word monomorphic. 
Accurate epidemiological data are hard to obtain; since in the past, BCA was included within nonpleomorphic tumors. BCA is quite rare and represents only 1% of all salivary gland tumors. The BCA occur more frequently in the parotid gland, followed by the minor salivary glands of the upper lip, buccal mucosa, and rarely on lower lip and palate. 
In the present case, the palatal location of the tumor represents a very unusual site. Extensive review of pertinent cases in PubMed and Medline data using keywords "basal cell adenoma of palate" and "basal cell adenoma of minor salivary glands" revealed only four cases ,,, [Table 2].
|Table 2: Review of literature of published case reports of basal cell adenoma of palate |
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The tumor can occur at any age, but is most common in middle-aged and older adults, with peak prevalence in the 7 th decade of life. In contrast to review of literature, present case occurred in 3 rd decade of life. 
Histologically, four characteristic patterns have been described: Solid, trabecular, tubular, and membranous. It is characterized by the presence of basaloid cellular layer with a stockade pattern and surrounded by hyaline substance.  The absence of myoepithelial cells, present in benign mixed tumors and other salivary gland neoplasms, has been referred as characteristic of this tumor. , However, in our present case we also observed positivity of calponin (calcium binding protein), SMA, and S100; indicating the role of myoepithelial cell proliferation in BCA, which is consistent with the finding reported by Gupta et al.,  and Montalli et al. 
Differential diagnosis of BCA must be established with some unfavorable entities such as basal cell adenocarcinoma, adenoid cystic carcinoma (AdCC), and basaloid squamous cell carcinoma as all these lesions show basaloid proliferation [Table 1]. So, there is need of IHC analysis to differentiate BCA from such prognostically different set of tumors, but unfortunately there was scarcity of comprehensive IHC analysis in literature published which can often lead to erroneous diagnosis. , Keeping this in mind we investigated BCA immunohistochemically using panel of markers.
CD117 (c-Kit) is a marker for AdCC,  and in present case it came out to be negative; thus, ruling out the possibility of AdCC. Ki-67 and p63 are expressed intensely in case of basal cell adenocarcinoma, basaloid squamous cell carcinoma, and AdCC; , but in our case, tissue section showed only focal staining and thus ruled out these lesions. In contrary to BCA, an infiltrative growth, more mitotic figures and Ki-67 staining of 5% of the cells are observed in basal cell carcinoma. Additionally, present case was positive for S100 and Pan CK indicating its relation to myoepithelial cells. Similar findings have also been reported by Gupta et al.,  and Montalli et al. 
Malignant transformation to basal cell adenocarcinoma is rare; however, few cases have been reported. Although recurrence is rare, the membranous subtype, which is a hereditary variety of BCA, has a 25-37% recurrence rate, possibly related to its multifocal nature, which impairs complete removal.  Management of benign tumors requires local soft tissue palatal excision. There is no need to fenestrate the palate and removal of bone is unnecessary. 
| > Conclusion|| |
Salivary gland tumors can show a striking range of morphological diversity between different tumor types and sometimes within an individual tumor mass. In addition, hybrid tumors, dedifferentiation and the propensity for some benign tumors to progress to malignancy can confound histopathological interpretation. Definitive diagnosis by clinical and imaging techniques alone is difficult. IHC plays an imperative role in diagnosis of salivary gland tumors to support the histological assessment. As it is difficult to delineate the exact behavior of lesions which are insufficiently reported in literature, a close regular follow-up after surgical treatment is mandatory.
| > References|| |
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[Figure 1], [Figure 2]
[Table 1], [Table 2]