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Am J Clin Pathol. 2009 Apr;131(4):574-9. doi: 10.1309/AJCPE68HZXCGWTKK.

Frequent expression of CD99 in anaplastic large cell lymphoma: a clinicopathologic and immunohistochemical study of 160 cases.

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  • 1Department of Pathology and Laboratory Medicine, Loma Linda University School of Medicine, Loma Linda, CA 92354, USA.


Originally described as a diagnostically useful marker for Ewing sarcoma, CD99 immunoreactivity has also been documented in a variety of other tumors, including hematopoietic neoplasms. By using conventional paraffin immunoperoxidase staining and tissue microarrays, we retrospectively investigated CD99 expression in a series of 160 anaplastic large cell lymphoma (ALCL) cases. Of the 160 cases, 103 (64.4%) were positive for CD99. The distribution of CD99 positivity was similar for nodal (66/103 [64.1%]), extranodal, (21/32 [66%]), and primary cutaneous lesions (16/25 [64%]). CD99 expression was present in 96 (64.4%) of 149 of the common type, 4 (80%) of 5 of the small cell variant, and 3 (50%) of 6 of the lymphohistiocytic variant cases. CD99 expression was slightly more frequent in anaplastic large cell lymphoma kinase (ALK)+ cases compared with ALK- cases (43/54 [80%] vs 44/81 [54%]). With 2 exceptions, ALK+ ALCL was seen only in patients younger than 41 years. We conclude that CD99 is frequently expressed in ALCL, with a slightly increased frequency in the younger age ALK+ cases. Nodal and extranodal ALCL should be considered in the differential diagnosis when a CD99+ neoplasm is encountered.

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