Correlation between CD30 mRNA and protein expression by tumor cells assessed by IHC in 238 PTCLs. Representative examples of the CD30 expression scores in PTCLs (A,C,E,G,I,K: hematoxylin and eosin; B,D,F,J,L: CD30 immunostaining by immunoperoxidase; H: double CD30/PAX5 immunostaining by immunoperoxidase, 3-amino-9-ethyl carbazole for CD30, and 3,3′ diaminobenzidine for PAX5, respectively; magnification ×40). (A-B) PTCL-NOS composed of small tumor cells with CD30 immunohistochemical score 0 (rare CD30⁺ cells, <5%). (C-D) PTCL-NOS composed of small/medium atypical cells with CD30 immunohistochemical score 1 (scattered tumor cells express CD30). (E-F) PTCL-NOS composed of medium/large tumor cells with immunohistochemical score 2. (G-H) AITL featuring a CD30 immunohistochemical score 2 (the CD30⁺ cells mainly correspond to CD30⁺/PAX5⁻ tumor cells, in addition to scattered CD30⁺/PAX5⁺ B blasts). (I-J) PTCL-NOS composed of medium/large tumor cells with CD30 immunohistochemical score 3. (K-L) EATL type 1 composed of large tumor cells with CD30 immunohistochemical score 4. Correlation between CD30 IHC scores and CD30 mRNA expression levels (M; histogram shown on the y-axis, red bars = high expression; blue bars = low expression). The regression line between mRNA and protein expression values is shown (blue); this line is used to project the mRNA expression value that distinguishes high- from low-CD30–expressing samples onto its corresponding IHC level (broken lines). Samples that express low levels of CD30 mRNA but that have high IHC scores are shown with a halo. Asterisks indicate points where 2 samples overlap.