Immunohistochemical analysis of PDGFRA, DDR2, EPHB1, RON, TRKB, and TRKA expression. Immunohistochemical analysis of patients with primary HL using alkaline phosphatase and Fast Red as substrate revealed the HRS cell–specific expression of PDGFRA (A), DDR2 (B), EPHB1 (C), RON (D), TRKB (E), and TRKA (F). In positive patients, most HRS cells were stained. In a clonally related composite lymphoma, PDGFRA-specific staining was observed in the HRS cells (G) but not in the follicular lymphoma cells (H). All magnifications are 200×; those in the inserts are 400×. (I) The percentages of patients with B-NHL (n = 86; 22 mantle cell lymphomas, 15 chronic lymphocytic leukemias, 19 follicular lymphomas, 11 Burkitt lymphomas, 19 diffuse large B-cell lymphomas), LP HL (n = 23), MC HL (n = 21), and NS HL (n = 19) expressing the indicated RTKs are shown. (J-M) Pie charts showing the breakdown of patients expressing the indicated numbers of RTKs for B-NHL (J) (n = 86), LP HL (K) (n = 23), MC HL (L) (n = 21), and NS HL (M) (n = 19).