Nonsebaceous lymphadenoma of salivary glands: proposed development from intraparotid lymph nodes and risk of misdiagnosis.

Nonsebaceous lymphadenoma (NSLA) is a rare benign salivary gland tumor composed of lymphoid and epithelial components. By definition, the epithelial component lacks sebaceous differentiation and instead displays a wide range of histological differentiation. In this study, we have collected nine cases of NSLA to characterize their histological and immunohistochemical profiles. The samples were histologically reviewed and immunohistochemical stains for CK5/6, CK7, CK14, CK18, p63, and Ki67 performed. Patients were six males and three females (mean age, 50 years). All tumors were located in the parotid gland and showed intimate intermingling of lymphoid tissue with islands or strands of epithelium with a wide spectrum of histological differentiation. The immunohistochemical profiles mirrored the epithelial differentiation; hence, areas with basaloid or lymphoepithelial differentiation strongly expressed CK5/6, CK14, and p63, while areas with ductal differentiation showed strong positivity for CK18/CK7 and CK5/6/CK14/p63 in luminal and basal cell layers, respectively. A hilus structure with salivary inclusions or D2-40 (podoplanin)-positive marginal sinus was identifiable in four and nine of the cases, respectively, supporting origin within intra-/periparotid lymph nodes. Six cases were initially misdiagnosed as other benign (n = 4) or malignant tumors (n = 2). Our study on the second largest series of NSLA reported to date provides strong evidence that NSLA belongs to the group of salivary gland tumors that pathogenetically develop from embryonic salivary gland inclusions in intra-/periparotid lymph nodes. Knowledge of the wide histological spectrum of this rare and presumably underreported tumor is important in order to avoid misdiagnosis, particularly as malignant tumor.