(a) Section of a paraffin-embedded lymph node from patient D.F. stained for ALK1 expression (alkaline phophatase-technique). Large pleomorphic tumor cells show marked cytoplasmic but no nuclear immunostaining. (b) G-banded partial karyotype of patient D.F. exhibiting the translocation t(1;2)(q21;p23) (arrows). (c) G-banded partial karyotype of patient S.N. showing the t(2;3)(p23;q21) (arrows) and, additionally, a +del(3)(p21).