Expression of IGF-IR and IGF-I in primary tumors from ALK⁺ ALCL patients. (A) Immunohistochemical staining of sections from a reactive lymph node shows that IGF-IR is weakly expressed in germinal center lymphocytes. The expression of IGF-IR is more pronounced in small lymphocytes and plasma cells in the mantle zone (400×). Of 12 ALK⁺ ALCL tumor samples, 10 demonstrated significant levels of expression of IGF-IR. Examples of 2 positive tumors are shown in panels B and C. (D) Immunohistochemical study of a reactive lymph node shows very low levels of expression of IGF-I in scattered small lymphocytes and plasma cells. Eight of 12 ALK⁺ ALCL tumors showed the expression of IGF-I. Two positive cases are illustrated in panels E and F. (E) The large infiltrating tumor cells are positive for IGF-I, and the background small benign lymphocytes are negative. (F) Lymph node architecture is replaced by tumor cells that are strongly positive for IGF-I. (G-H) Illustrated are 2 ALK⁺ ALCL cases where the lymphoma cells are negative for IGF-I.