Grading follicular lymphomas in fine-needle aspiration biopsies - The role of ThinPrep and flow cytometry

BACKGROUND. The World Health Organization (WHO) recommends a 3-tier grading system (Grades 1-3) for follicular lymphomas (FLs) based on the absolute number of centroblasts per high-power microscopic field (HPF) in 10 neoplastic follicles. Grades 1 and 2 FL are still managed as indolent FLs, whereas Grade 3 FL is thought to behave more aggressively. In this study, the feasibility of grading FL using ThinPrep (TP) slides and flow cytometry (FC) was evaluated. METHODS. Fifty-three cases of lymph node fine-needle aspiration (FNA) from patients with histologically confirmed FL (20 Grade 1, 17 Grade 2, and 16 Grade 3) were included. The number of centroblasts present in 300 lymphoid cells and in 10 HPF in TP Papanicolaou-stained slides was evaluated. The percentage of CD10-positive small cells was calculated with FC results. Statistical analysis was performed with the Jonckheer-Terpstra nonparametric trend test and the Wilcoxon rank sum test. RESULTS. The statistical analysis demonstrated a significant upward trend in the number of centroblasts as the grades increased. Also, all 3 methods had statistically significant results to distinguish different grades of FL, except when FC was used to distinguish Grade 2 from Grade 3 FL. CONCLUSIONS. Counting centroblasts, either in 300 lymphoid cells or per 10 HPF in TP slides, represented a statistically significant method to separate different grades of FL in FNA samples. Analysis of cell size by FC was not as reliable to distinguish different grades of FL, especially Grade 2 from 3.