Due to the large size of the mass, and given the differential diagnosis, a decision was made to obtain a tissue sample under local anesthesia for histopathologic analysis. A 1 cm X 0.5 cm wedge of tissue was obtained from the lateral aspect of the mass, in the vicinity of the left maxillary tuberosity. Care was taken to incise deep into mass to avoid missing its core. Of interest, there was minimal bleeding and the tissue had the consistency of cutting through a soft rubber ball. Local measures were applied to obtain hemostasis and no sutures were placed over the surgical defect. A gauze pressure dressing was also applied to the area.

Incisional Biopsy

The histologic diagnosis of this case was rendered by Drs. Thomas Morton (Oral Pathology Service) and Sindhu Cherian (Hematopathology Service) from the University of Washington. Histologic examination reveals a hemisected piece of soft tissue composed of surface epithelium with underlying fibrous connective tissue intensely infiltrated by sheets of medium-to-large-size blue cells consistent with B-lymphocytes (Figures 2 & 3. These cells have large nuclei with vesicular chromatin pattern and multiple nucleoli arranged haphazardly (Figure 3). A few cells with large nuclei and prominent centrally located nucleoli are also present. A few macrophages with tangible bodies are also present. This neoplasm shows high mitotic activity as demonstrated by the H & E histology and by the Ki-67 antibody stain (approximately 90% mitosis) (Figure 4). The immunohistochemistry staining was positive for PAX5, CD20 (Figure 5) and Ki-67 (Figure 4).

Figure 2 Low power (x40) H & E histology demonstrates a piece of mucosa infiltrated by diffuse sheets of monotonous medium to large size blue cells. The nuclei are large, most with multiple nucleoli and some with centrally located prominent nucleoli. Scattered macrophages with tangible bodies are also present.

Figure 3 Higher power (x400) H & E histology demonstrates closer look at the atypical medium size to large round cells with large oval to round nuclei and high mitotic activity.

Figure 4 Low power (x40) Immunohistochemistry stain demonstrate that the neoplastic cells are uniformly positive with Ki-67 with approximately 90% mitotic rate.

Figure 5 Low power (x400) Immunohistochemistry stain demonstrate that the neoplastic cells are variably positive with CD-20.