Oncocytic carcinoma of lip: A rare neoplasm of minor salivary gland.

Oncocytic carcinoma is an extremely rare neoplasm of the salivary gland, with only a few cases reported in literature till date. We report the occurrence of this rare lesion in lip in a 43-year-old female presenting with a progressively increasing swelling for which excision was done. Fine needle aspiration was done and the smears revealed tumor cells with well-defined cell borders, round to oval, central to eccentrically located moderately pleomorphic nuclei with fine chromatin, prominent nucleoli and abundant eosinophilic granular cytoplasm. Microscopic examination of the resected tumor showed solid sheets, nests, islands and cords of oncocytic cells diffusely infiltrating the surrounding tissues. After 5 months, the patient again presented with bilateral submandibular and right axillary lymphadenopathy revealing metastatic deposits from oncocytic carcinoma. We report this case of oncocytic carcinoma because of its unusual location, the minor salivary gland of lip being a rare site for the tumor.

Introduction

Neoplasms that arise in salivary gland are rare and yet they represent a wide variety of benign and malignant histological subtypes. Salivary gland neoplasms make up 1% of all head and neck tumors. Among these, 80% arise in parotid gland, 10-15% in submandibular gland and the remainder in sublingual and minor salivary glands. Oncocytes are most abundant in the parotid gland; they are also found in other major and minor salivary glands as well as in the larynx, trachea, bronchi, oesophagus, nasal mucous membranes, thyroid, parathyroid, pancreas, liver, and stomach. Although focal oncocytic features are seen in a wide variety of salivary neoplasms, pure oncocytic carcinoma of salivary gland origin is rare.[1] Most cases of oncocytic carcinoma have occurred in the parotid glands, but recent reports have described tumors that involved the submandibular gland and minor glands of the palate, nasal cavity, and ethmoid and maxillary sinuses. We describe a new case of oncocytic carcinoma that arose in the minor salivary gland and metastasized to lymph nodes.

Case Report

A 43-year-old female presented with progressively increasing painless swelling on the lower lip for 25 days. Physical examination revealed a fixed hard 3 × 3 cm mass on the lower lip. Regional lymph nodes were not enlarged. Fine needle aspiration (FNA) of mass was done. Smears showed tumor cells scattered singly and in multilayered sheets. These cells had well-defined cell borders, round to oval, central to eccentrically located moderately pleomorphic nuclei with fine chromatin, prominent nucleoli and abundant eosinophilic granular cytoplasm. An occasional atypical mitosis was also seen. Cytological diagnosis of oncocytic carcinoma was suggested. Surgical excision of the swelling was done and the specimen was submitted for histopathological examination.

Pathological findings

Gross examination revealed a well-circumscribed, firm, grey white tumor measuring 3 cm in diameter.

Microscopically, a neoplasm with infiltrative growth pattern consisting of large, round to polyhedral cells in solid sheets, islands and cords with abundant eosinophilic granular cytoplasm was seen. A histopathological diagnosis of oncocytic carcinoma of minor salivary gland was made. Streptavidin–biotin immunohistochemical study was performed on paraffin-block sections by the standard labelled method. The primary antibody was a mouse monoclonal antihuman mitochondrial antibody (DAKO-LSAB kit, K0675). Immunohistochemically, oncocytic cells showed intense finely granular immunoreactivity in the cytoplasm. After 5 months, the patient again presented with bilateral submandibular and right axillary lymphadenopathy. FNA was done from these lymph nodes and the smears prepared revealed similar morphology suggesting metastatic deposits from oncocytic carcinoma [Figure 1a–d].

Figure 1

(a) FNA from swelling lip showing pleomorphic oncocytic cells (MGG, ×200). (b) Cytoplasmic positivity revealed by the oncocytic cells using antimitochondrial antibody (IHC, ×400). (c) Oncocytic carcinoma: Photomicrograph showing mitosis (H and E, ×400). (d) FNA from submandibular lymph node showing metastatic deposits from oncocytic carcinoma (MGG, ×400)

Discussion

Oncocytic carcinoma of salivary gland origin is rare and rarest when it arises in minor salivary gland. Bauer and Bauer[2] reported the first case in 1953. Most cases of oncocytic carcinoma have occurred in parotid glands, and some have been described in submandibular gland and minor salivary glands. The terms oncocytic carcinoma, malignant oncocytoma, oncocytic adenocarcinoma and malignant oxyphilic adenoma are synonymous.[3] They have been estimated to represent only 5% of all oncocytic neoplasms and 0.0005% of all salivary gland tumors.[4] They are characterized by oncocytes with marked cellular atypia, frequent mitosis, destruction of adjacent organs, perineural or vascular invasion and distant or regional lymph node metastasis. Various benign and malignant salivary gland neoplasms may have foci of oncocytic cells, but the oncocytic component usually comprises such a small portion that is unlikely to be confused with oncocytic carcinoma. Oncocytosis is non-neoplastic proliferation of oncocytes that can be differentiated from oncocytic carcinoma by the presence of multiple foci of oncocytic cells within salivary gland lobules without altering the normal architecture. Tumors with significant oncocytic component include Warthin's tumor, oncocytoma and oncocytic carcinoma.[5] Other neoplasms that arise from salivary gland with a granular cytoplasm are oncocytoma, acinic cell carcinoma and salivary duct carcinoma. Oncocytoma can be differentiated by the presence of a well-differentiated connective tissue capsule. Moreover, compared to oncocytoma, oncocytic carcinoma shows greater nuclear pleomorphism and mitotic activity. Malignant nature of the neoplasm can be recognized by its morphological features and infiltrative growth pattern.

Acinic cell carcinoma can be differentiated from oncocytic carcinoma by the presence of amphophilic or basophilic granules in the cytoplasm of tumor cells and their predominant microcystic and papillary growth pattern. Salivary duct carcinoma, in contrast, forms duct like spaces with papillary and cribriform growth pattern and also shows comedo necrosis. In addition, immunohistochemically, oncocytic cells show positivity for mitochondrial antigen, keratin and alpha-1-antichymotrypsin.[6] Electron microscopy reveals numerous mitochondria filling the cytoplasm of oncocytic cells. Shintaku and Honda[7] reported that immunohistochemistry with antimitochondrial antibody is highly sensitive and specific for light microscopic identification of mitochondria and superior to routine HandE staining, especially for the detection of isolated oncocytic cells. In this patient, the immunohistochemical study with antimitochondrial antibody revealed intense immunoreactivity of the cytoplasm in the tumor cells.

Despite being described five decades ago, not much is known about these rare tumors. The biological behavior cannot be evaluated fully because of the paucity of cases reported and the lack of follow-up information. However, the main treatment modality is surgery with or without adjuvant radiotherapy. Radiation does not appear to favorably alter the biologic behavior of this tumor. Goode and Corio[4] reported that tumors smaller than 2 cm in diameter appeared to be associated with better prognosis than those that were larger.

Presence of distant rather than local lymph node metastasis is the most important prognostic indicator. However, clinical course and prognosis of patients with oncocytic carcinoma remains to be evaluated as more cases are being reported.