PRDM1 gene is inactivated in ALCL samples. (A) Representation of the aberrations, and their size, affecting the PRDM1 locus (6q21). Blue bars represent loss; light blue bars represent homozygous deletion (hdel). (B) Results of sequencing and mutational analysis of PRDM1 coding exons in 46 ALCL samples (31 ALK⁻ and 15 ALK⁺ samples) and in 7 ALCL cell lines (5 ALK⁺ and 1 ALK⁻ cell line and 1 cALCL). Red triangles are new mutations in 2 different ALK⁻ samples. (C) View of the single nucleotide changes in different sequences. (D) Immunohistochemistry results for BLIMP1 staining: BLIMP1 staining was evaluated on TMA obtained from an independent series of ALCL samples. TMA samples were considered negative or positive for BLIMP1 depending on the intensity of the staining. A representative case for each condition, BLIMP1 negative (left panel), BLIMP1 positive only at cytoplasmic level (middle panel), BLIMP1 positive only at a nuclear level (right panel), is reported (magnification, ×40). TMA, tissue microarray.