|Ahead of print publication
Acinic cell carcinoma of the posterior buccal mucosa: A rare case report
Sharlene Sara Babu1, S Sunil1, Akhilesh Prathap2, Anuna Laila Mathew3
1 Department of Oral and Maxillofacial Pathology, Pushpagiri College of Dental Sciences, Thiruvalla, Kerala, India
2 Department of Oral and Maxillofacial Surgery, Pushpagiri College of Dental Sciences, Thiruvalla, Kerala, India
3 Department of Oral Medicine and Radiology, Pushpagiri College of Dental Sciences, Thiruvalla, Kerala, India
Sharlene Sara Babu,
Department of Oral and Maxillofacial Pathology, Pushpagiri College of Dental Sciences, Thiruvalla, Kerala
Source of Support: None, Conflict of Interest: None
Acinic cell carcinoma (ACC) is a low-grade malignant salivary gland neoplasm that comprises approximately 17% of primary salivary gland malignancies or about 6% of all salivary gland neoplasms. The most common intraoral sites are the buccal mucosa, lips, and palate. The diagnosis of ACC frequently presents difficulties, owing to its great radiological and cytological similarity with benign tumors and with normal acinar component of the salivary gland, respectively. The management of ACC consists of complete surgical excision. Here, we report a case of ACC on the left retromolar trigone, a rare location in a 44-year-old female.
Keywords: Acinic cell carcinoma, minor salivary gland, salivary gland neoplasm
| > Introduction|| |
Acinic cell carcinoma (ACC) is a malignant epithelial neoplasm of the salivary glands in which at least some of the neoplastic cells demonstrate serous acinar cell differentiation characterized by cytoplasmic zymogen secretory granules. About 81%–98% of the cases occur in the parotid gland, 11% in the submandibular gland, <1% in the sublingual gland, and 3%–12% in the minor salivary glands. ACC was referred to as an entity for the first time >50 years ago by Godwin et al. The terms “acinar” and “serous” refer to the histologic resemblance of tumor cells to the secretory parenchymatous cells of the parotid, grouped in grape-like clusters and hence given the Latin name “acinus.” In the past, the malignant nature of this cancer had been disputed or gone unrecognized. In earlier literature, it was classified as an “acinic cell tumor” or benign “adenoma.” Recent literature detailing the high potential for recurrence, metastases, and even death resulted in the WHO reclassification “malignant carcinoma” due to the high potential for recurrence, metastases, and even death. The most common intraoral sites for ACC are the buccal mucosa, lips, and palate. Minor salivary gland tumors are rarely seen in the inferior anatomic regions such as the retromolar trigone and the floor of mouth compared to the superior regions such as the palate. Here, we report a retromolar trigone ACC, a rare location in the oral cavity.
| > Case Report|| |
A 39-year-old female patient presented with a chief complaint of a gradually increasing swelling on the upper back portion of the left cheek of 2-year duration [Figure 1]. Fine-needle aspiration cytology was done 1.5 years back with no relevant finding. The patient noticed bleeding from the swelling due to trauma from teeth for 2 weeks. There was no relevant medical and family history. On intraoral examination, a bright red-colored, soft, smooth-surfaced, oval-shaped, pedunculated lesion with nonindurated irregular border was noticed on the left posterior buccal mucosa adjacent to the maxillary left second molar. There was no associated lymphadenopathy. Computed tomography scanning was done [Figure 2]. A provisional diagnosis of pyogenic granuloma, hemangioma, and minor salivary gland tumor was made. An excisional biopsy was done after routine blood examination, and tissue was sent for histopathological examination. On gross examination, an oval, soft, pink-colored, smooth-surfaced mass with irregular border was noticed. The hematoxylin- and eosin-stained serial sections showed stratified squamous epithelium overlying a moderately collagenous and highly cellular connective tissue. The underlying connective tissue was composed of proliferating tumor cells in the form of sheets along with numerous vascular channels engorged with red blood cells. Tumor cells were vacuolated round cells showing pleomorphism and hyperchromatism. Some cells appeared morphologically similar to acini. Clusters of clear cells, dilated duct-like spaces with eosinophilic material, and a few cyst-like spaces were also noted [Figure 3], [Figure 4], [Figure 5]. A differential diagnosis of hemangioendothelioma and ACC was made. Special staining with periodic acid–Schiff (PAS)–diastase showed positivity [Figure 6]. Immunohistochemical stainings showed positive pancytokeratin and negative CD34 and CD31 [Figure 7], [Figure 8], [Figure 9]. A final diagnosis of ACC was made. The patient was reviewed after 1 month [Figure 10].
|Figure 1: Clinical photograph showing pedunculated erythematous mass on the left posterior buccal mucosa|
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|Figure 3: Photomicrograph showing stratified squamous epithelium overlying a moderately collagenous and highly cellular connective tissue (H and E, ×4)|
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|Figure 4: Photomicrograph showing connective tissue composed of proliferating tumor cells in the form of sheets along with numerous vascular channels engorged with red blood cells. Tumor cells were vacuolated round cells showing pleomorphism and hyperchromatism. Some cells appeared morphologically similar to acini (H and E, ×10)|
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|Figure 5: Photomicrograph showing connective tissue composed of clusters of clear cells, dilated duct-like spaces with eosinophilic material, and a few cyst-like spaces (H and E, ×40)|
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|Figure 6: Photomicrograph showing positive staining with periodic acid–Schiff–diastase|
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| > Discussion|| |
Salivary gland tumors comprise about 0.6% of all cancers. In AFIP data of salivary gland neoplasms, ACC is the third most common malignant salivary gland neoplasm after mucoepidermoid carcinoma and adenocarcinoma. In these data, ACC comprises 17% of primary malignant salivary gland tumors or about 6% of all salivary gland neoplasms. The ACC occurs predominantly in persons in middle age or somewhat older, the mean age being 44 years. Women are affected more than men (3:2). It has also been encountered in 12% of the patients before the age of 20 years. In the pediatric age group, ACC is the second most common epithelial malignancy following mucoepidermoid carcinoma. Possible causes of ACC include previous radiation exposure and familial predisposition. Recently, a chronological association between onset and recurrence of ACC and pregnancy is noticed. Long-term follow-up studies of the survivors of the atomic bomb explosions in Hiroshima and Nagasaki show an increased relative risk of 3.5 for benign and 11 for malignant salivary neoplasms. Therapeutic radiation, particularly of the head-and-neck region, has been linked with a significantly increased risk of developing salivary gland cancers. There appears to be a risk from iodine 131 used in the treatment of thyroid disease, as the isotope is also concentrated in the salivary glands. Workers in a variety of industries have an increased incidence of salivary gland carcinomas in general. These industries include asbestos and rubber manufacturing, exposure to metal in the plumbing industry and nickel compounds, woodworking in the automobile industry, and employment in hairdressing and beauty shops. Endogenous hormones have been reported in normal and neoplastic salivary glands, but some of the results have been conflicting. Estrogen receptors have been reported in a minority of cases of ACC, mucoepidermoid carcinoma, and salivary duct carcinoma. Progesterone receptors and androgen receptors were also seen in some cases of ACC. These findings raised suspicion that some of the salivary gland neoplasms including ACC might be hormonally dependent like breast carcinoma. The genetic alterations linked to ACC of the parotid gland included alterations at chromosomes 4p, 5q, 6p, and 17p, suggesting the association of tumor suppressor genes with the oncogenesis of these tumors. Moreover, deletions of chromosome 6q, loss of Y, and trisomy 21 have been reported in association with ACC., Further molecular studies indicated that retinoblastoma pathways, which are common to the most human tumors, might also be involved in the pathogenesis and etiology of ACC. The ACC closely resembles the pleomorphic adenoma in gross appearance and tends to be encapsulated and lobulated. This tumor presents as a slowly growing, mobile, or fixed mass of various durations. Usually asymptomatic but pain or tenderness is seen in over one-third of the patients. Facial muscle weakness may be seen. Patients with bilateral synchronous tumors have been reported.
Histopathologic features of the ACC, which is frequently surrounded by a thin capsule, may be composed of cells of varying degrees of differentiation. Well-differentiated cells bear remarkable resemblance to normal acinar cells, whereas less differentiated cells resemble embryonic ducts and immature acinar cells. Abrams et al. have described four growth patterns: (1) solid, (2) papillary-cystic, (3) follicular, and (4) microcystic. In general, one pattern predominates although combinations can occur. The most characteristic cell seen has the features of the serous acinar cells, with abundant granular basophilic cytoplasm and a round darkly stained eccentric nucleus. Other cells seen are the intercalated duct-like cells, which are smaller and the vacuolated cells which seem to be unique to ACCs among salivary gland neoplasms. Connective tissue stroma is delicately fibrovascular collagenous tissue. Ellis and Auclair reported that mucous cells and the absence of serous acinar cells should readily distinguish cystadenocarcinoma and mucoepidermoid carcinoma from ACC. In terms of cell types, a positive reaction for S-100 protein and focal positive reactions for PAS, PAS with diastase digestion, and amylase were observed in our case. This suggests that the tumor cells differentiated not only into intercalated duct cells but also into serous acinar cells, and the intercalated duct cells proliferated predominantly more than the serous acinar cells.
The treatment of ACC in most cases has been surgical. ACC confined to the superficial lobe of the parotid gland is best treated by lobectomy; for those in the deep lobe, total parotidectomy is usually necessary. The facial nerve may need to be sacrificed if it is involved by tumor. Submandibular tumors are managed by total removal of the gland, and minor gland tumors are treated with assured surgical excision. Lymph node dissection is not indicated unless there is clinical evidence of metastatic disease. Adjunctive radiation therapy may be considered for uncontrolled local disease. Radiation therapy should be considered in cases with positive surgical margins, multiple positive lymph nodes, and vascular or perineural invasion. The ACC is associated with one of the better prognoses of any of the malignant salivary gland tumors. Approximately one-third of patients have recurrences locally, and metastases develop in 10% to 15% of patients. About 6%–26% of patients die of their disease. Metastatic progression occurs through the lymphatics to cervical lymph nodes and spreads hematogenously to the lungs or bones. The prognosis for minor gland tumors is better than that for tumors arising in the major glands.
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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