Grading of Follicular Lymphoma: Comparison of Routine Histology With Immunohistochemistry

Abstract Context.—Follicular lymphoma (FL) grading is based on the average number of large transformed cells in 10 neoplastic follicles at ×40 high-power field (×10–40 high-power field) examination (grade 1, 0–5 centroblasts per high-power field; grade 2, 6–15 centroblasts per high-power field; grade 3, >15 centroblasts per high-power field). Objective.—Since there may be significant interobserver variability, we analyzed the usefulness of immunohistochemical stains in grading FLs more reliably. Design.—Forty-three FLs initially graded by World Health Organization criteria (grade 1, 12; grade 2, 18; grade 3, 13) were reviewed and stained with CD3, CD20, Ki-67, CD30, CD68, PAX-5, and BCL-6. Retrospective review was performed for the average number of large cells, of large lymphoid cells, of large cells staining with CD3, CD20, BCL-6 (40 cases), and PAX-5, and of all cells staining with CD68, Ki-67, and CD30. Results.—By histologic review, 8 of 43 FLs had a significant grade change (4 cases upgraded and 4 c...