Cytomorphological features of lymphoepithelial carcinoma of submandibular gland in an adolescent male.

A case of lymphoepithelial carcinoma (LEC) occurring in right submandibular gland of a 13-year-old Indian male is presented, wherein the lesion unveiled itself only after multiple fine needle aspiration (FNA) procedures. This unusual neoplasm has high frequency of occurrence in Eskimos and a predilection for the parotid gland. The aspirates obtained were highly cellular comprising tight clusters of atypical epithelial cells with admixture of lymphocytes. Histopathological examination of the resected submandibular gland and lymph node chain was consistent with the diagnosis of LEC. Immunohistochemistry (IHC) revealed cytokeratin (CK)-positive and S-100-negative tumor cells lying admixed with CD45-positive lymphoid cells. A detailed otorhinolaryngological examination with inclusion of multiple biopsies was found negative for any primary tumor. Although histopathological features of this entity are well established, only a handful of case reports describing cytological features of this entity are present in medical literature. We conclude that the cytomorphological features of LEC are sufficiently distinctive to at least, suggest a possibility of this lesion.

Introduction

Lymphoepithelial carcinoma (LEC) of salivary gland is a rare neoplasm with a striking geographic and ethnic distribution with a vast majority occurring in North Americans, Greenland Eskimos and Asian Orientals.[1] The parotid gland is involved in more than 90% of tumors, with the submandibular gland being an uncommon site.[2] A high proportion of these tumors show consistent association with Epstein-Barr virus (EBV).[1] Although a variant of undifferentiated carcinoma, the prognosis seems to be better than other undifferentiated carcinomas of salivary gland, probably because lymphoid stroma has a role in limiting the aggressiveness of this lesion.[3]

Case Report

A 13 year old male presented with a hard, fixed 4 × 4-cm mass located in the right submandibular region. The aspiration yielded highly cellular smears comprising markedly atypical epithelial cells disposed in cohesive clusters and few small groups. The cells were large, polygonal with high nucleocytoplasmic ratio and indistinct cytoplasmic borders. The nuclei were highly pleomorphic, vesicular with prominent nucleoli [Figure 1]. An intimate intermingling of mature lymphocytes within these epithelial clusters was seen. A diagnosis of metastatic poorly differentiated carcinoma was suggested.

Figure 1

Highly cellular smears showing cohesive aggregates of atypical epithelial cells lying against a background of mature lymphocytes (H and E, x100). Inset shows atypical cells having indistinct cytoplasmic borders, large vesicular nucleus with single to multiple prominent nucleoli and finely granular chromatin (H and E, ×1000)

Excision of right submandibular gland with radical neck dissection was performed. The resected specimen consisted of 4 × 3-cm mass replacing the normal gland. The cut surface was grey-white and lobulated. The lymph node chain consisted of eight enlarged lymph nodes, three of which had a grey-white cut surface. The microscopic examination disclosed a malignant neoplasm characterized by anastomosing cords, syncytial nests and islands of highly undifferentiated cells with indistinct borders, eosinophilic cytoplasm, large vesicular nuclei and single to multiple prominent nucleoli [Figure 2a]. Frequent mitotic figures were also seen. The epithelial component was sharply demarcated from stroma consisting of diffuse sheets and aggregates of lymphoid cells forming germinal centres at few places as well as fibrosis. Microscopically, four out of 10 lymph nodes showed metastatic deposits. A diagnosis of LEC was made with a suggestion to rule out metastatic nasopharyngeal carcinoma. A detailed otorhinolaryngological examination was undertaken with inclusion of multiple site biopsies which were negative for malignancy. Immunohistochemistry (IHC) demonstrated CK-positive and S-100-negative tumor cells intermingled with CD45-positive lymphoid cells [Figure 2b, c] thereby, clinching the diagnosis of primary LEC of submandibular gland.

Figure 2

(a) Histopathological section of LEC showing nests and islands of tumor cells embedded in a densely lymphoid and fibrotic stroma (H and E, ×400); (b) Pan-CK immunostain highlighting tumor cells (IHC, ×1000); (c) CD45 decorating the interspersed lymphoid cells (IHC, ×1000)

Discussion

LEC is an unusual type of squamous cell carcinoma predominantly occurring in the upper aero-digestive tract.[1] Primary LEC occurring in the salivary gland is extremely rare accounting for 0.4-1.0% of the epithelial tumors of the salivary gland.[2] This lesion displays a mysteriously strong racial predilection with the age at presentation ranging from 20 to 60 years and female to male ratio of 1.5:1.[13]

The parotid gland is the favored site for LEC of salivary gland constituting more than 90% of lesions.[124] The ratio of LEC of the parotid gland to submandibular gland in accumulated cases in literature is 17:1.[5] A strong association of LEC with EBV is noted. Although important pathogenetically, EBV does not seem to influence the prognosis of these lesions.[1]

Most LEC develop de novo with only a subset of cases arising from benign lymphoepithelial lesion (BLEL).[36] Hilderman et al[7] described a malignant lesion of parotid gland that resembled BLEL and called it ‘malignant lymphoepithelial lesion (MLEL)’. This obfuscatory term was replaced by ‘lymphoepithelial carcinoma (LEC)’ after the squamous epithelial origin was confirmed by electron microscopic studies of Kott et al.[1]

Although medical literature is replete with case reports describing histopathological features of LEC, only a handful of case reports describing the cytopathological features of this lesion exist. The earliest description of cytological features of this entity was made by Gunhan et al.[8] and Thompson et al.[4] in parotid lesions. Characteristically, the smears are cellular comprising biphasic population of cells with one component of poorly differentiated epithelial cells exhibiting marked pleomorphism, high nucleocytoplasmic ratio, vesicular nuclei with finely granular chromatin and prominent nucleoli. The other component consists of mature lymphocytes with occasional macrophages.[4]

Before establishing a diagnosis of primary LEC of the salivary gland, it is essential to exclude metastasis from an undifferentiated carcinoma. Anatomically, nasopharyngeal lymphoepithelioma is the most likely candidate to metastasize to this area.[8] According to Gunhan et al.,[8] the cytological proof of malignancy in cases of primary or metastatic LEC is generally easy but, specifying the type of lesion as LEC may be difficult. The characteristic cytological features of cohesive large epithelial cell clusters intermingling with mature lymphocytes, histiocytes and plasma cells seen in LEC, are similar to those seen in nasopharyngeal carcinoma. The distinction between these two entities is difficult and depends on careful clinical evaluation. Histopathologically, the presence of BLEL adjacent to the tumor is helpful but, multiple site biopsies from the upper aerodigestive tract are mandatory to rule out nasopharyngeal carcinoma.[1]

The cytological differential diagnosis for nasopharyngeal lymphoepithelioma are also valid for LEC of salivary gland and include large cell lymphoma and poorly differentiated carcinoma of various organs.[8] Differentiation from large cell lymphocytic and histiocytic neoplasm is helped by IHC markers like CD20, CD45RO, CD68, Leu-1, Ki-67 and epithelial markers. Another differential diagnosis is amelanotic melanoma where marker proteins like anticytokeratins, anti-S100 and anti-HMB-45 help.[1] In the present case, IHC confirmed the lesion as LEC.

Although most case reports describe the cytological smears of LEC as moderately to highly cellular,[248] in the present case the lesion remained masked despite two FNA attempts due to scant cellularity. Jang et al.[1] have also made a brief mention regarding the sparse cellularity of smears consisting of atypical cells intermingled with lymphocytes. Thus, the lesion may remain cryptic and the cytopathologist must not refrain from a repeat FNA or biopsy if the clinical suspicion is high.

Conclusions

Although a rare entity, LEC must be considered in the differential diagnosis when a cytopathologist is confronted with aspirates comprising atypical epithelial cells admixed with lymphocytes. The lesion may remain masked under the garb of reactive lymphadenitis or due to scant cellularity, warranting repeat aspiration/biopsy if the clinical suspicion is high. The presence of large undifferentiated cells with prominent nucleoli and fine chromatin, admixed with lymphocytes in cytology aspirates are fairly distinctive to at least suggest a possibility of LEC.