A 51-year-old man was admitted to the hospital with two month history of painless mass that was located anterior to the right ear. In physical examination, there was a 2 cm, mobile mass in the right parotid gland and the presumptive clinical diagnosis was pleomorphic adenoma. Past medical history was insignificant. Laboratory tests including complete blood count and blood biochemistry were normal. The patient underwent a superficial parotidectomy.
The gross examination showed a 1.7 cm, white-tan, firm solid mass located within the parotid gland substance (Figure 1). Microscopically, there was a lymph node within otherwise normal parotid tissue. The lymph node architecture was effaced by atypical lymphoid cell infiltration which had geographical configuration without recognisable follicle formation (Figure 2). The atypical cells were medium to large sized with oval to round, vesicular nuclei that were occasionally indented. The chromatin pattern was fine and nucleoli were located mostly peripherally (Figure 3).
Immunohistochemicaly, the atypical lymphoid cells were strongly positive for B-cell-associated antigens (CD20, CD79a) and were also positive for Bcl-2 and Bcl-6 (Figures 4, 5 and 6). There was no staining with CD5, CD15, CD21, CD23, CD30, CD1a, CD68, ALK and EMA. The proliferation index using Ki- 67 was approximately 60%.
What is your diagnosis?
Follicular lymphoma, grade 3, geographic pattern.