(A and B) Immunohistochemical demonstration of BCL-6 protein expression in a CD30⁺ anaplastic large-cell lymphoma employing the APAAP method on frozen tissue sections. (A) In this field several tumor cells show a nuclear staining pattern with anti–BCL-6 MoAb PG-B6. (B) Anaplastic large cells show strong nuclear immunoreactivity with the anti–BCL-6 MoAb PG-B6. The positivity is microgranular. (C) Coexpression of BCL-6 protein (nuclear, blue) is observed in a proportion of CD30⁺ (cytoplasmic and membranous, reddish) anaplastic large tumor cells, as detected by two-color staining (see Materials and Methods). Original magnification (A) ×250, (B) ×400, and (C) ×400.