Classical Hodgkin disease.

(A) Radioactive in situ hybridization with a probe specific for Oct2 mRNA. In contrast to bystander B cells, HRS cells remained completely unlabeled (arrows). (B) Immunostaining for Oct2. All HRS cells are unlabeled. (C) Immunostaining for Oct2. A proportion of HRS cells is positive. (D) Immunostaining for BOB.1/OBF.1. HRS cells are negative. All immunolabeling reactions were performed with the APAAP technique.