Sections from FFPE tissue samples were used to build TMAs. During pathological review of each section, areas containing malignant follicles, representative of the entire biopsy sample and avoiding fibrotic portions were marked on the paraffin blocks. Cylinders that were 1 mm in diameter from three different areas were then collected and included in the TMA blocks. After dewaxing and pressure-cooker antigen retrieval, immunostaining was conducted in an automated immunostainer (Dako, Glostrup, Denmark) using a standard avidin–biotin–peroxidase technique. The primary antibodies (EZH2, H3K27me2 and H3K27me3) and staining conditions were used as previously described.19 (link) Deparaffinization, rehydration, epitope retrieval and staining were performed as described by Dubois et al.19 (link) Slides were scored in a blinded fashion by three experienced anatomopathologists (LX, ST, LM). Tumors were scored according to the proportion of tumor cells stained (0–10, with 0 representing negative staining, 1 representing 1–10% positive tumor cells and 10 representing 91–100% positive tumor cells). For each patient, the methylation score was adapted from Dubois et al. as follows:
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