Immunoreactivity of CD99 in non-Hodgkin's lymphoma: unexpected frequent expression in ALK-positive anaplastic large cell lymphoma

Abstract

To verify the spectrum of CD99-expressing lymphoid malignancy, an immunohistochemical study for CD99 was carried out in 182 cases of non-Hodgkin's lymphoma, including 21 lymphoblastic lymphomas, 11 small lymphocytic lymphomas, 9 mantle cell lymphomas, 12 follicular lymphomas, 37 diffuse large B cell lymphomas, 18 Burkitt's lymphomas, 28 NK/T-cell lymphomas, 8 angioimmunoblastic T-cell lymphomas, 23 peripheral T-cell lymphomas, unspecified, and 15 systemic anaplastic large cell lymphomas. CD99 was positive in all T-lymphoblastic lymphomas and in 60% of B-lymphoblastic lymphomas. Majority of T and NK cell lymphomas were negative for CD99, except anaplastic large cell lymphomas (ALCLs). Eight of 15 cases (54%) of ALCLs reacted with anti CD99 antibody. Seven of 10 (70%) ALK positive ALCLs expressed CD99, whereas only 1 of 5 (20%) ALK negative ALCLs were positive. Of the mature B-cell lymphomas, 5.4% (2/37) of diffuse large B cell lymphomas and 11.1% (2/18) of Burkitt's lymphomas expressed CD99. In conclusion, CD99 is infrequently expressed in mature B and T cell lymphomas, except ALK-positive ALCL. High expression of CD99 in ALK-positive ALCL is unexpected finding and its biologic and clinical significances have yet to be clarified.

Fig. 1

(A) Anaplastic large cell lymphoma. H & E stain (×400). (B) Anaplastic large cell lymphoma, CD30 expression (×100). (C) Anaplstic large cell lymphoma, ALK protein (×100). (D) Anaplastic large cell lymphoma, CD99 expression (×100). (E) Anaplastic large cell lymphoma. Higher magnification of CD99 immunostain (×400).

Fig. 2

Western blot analysis using CD99 antibody shows positive band of 33 kDa in size. N, negative control; 1, anaplastic large cell lymphoma; P, positive control (lymphoblastic lymphoma).