ABSTRACT
<p><b>OBJECTIVE</b>To investigate co-expression of CD99/MIC2 and anaplastic lymphoma kinase (ALK) protein in anaplastic large-cell lymphoma (ALCL) tissues and Karpas 299 cells and its significance.</p><p><b>METHODS</b>Clinical prognoses and ALK protein expressions of 25 cases of ALCL were reviewed retrospectively, the median duration of survival was analyzed for patients with ALK(+) ALCL and ALK(-) ALCL. Histological and immunohistochemical staining were applied to other 25 cases of ALCL and paraffin-embedded tissue from human anaplastic large-cell lymphoma Karpas 299 cells to detect the protein of CD99 and ALK.</p><p><b>RESULTS</b>Of former 25 cases of ALCL, median duration of survival for ALK(+) patients was 59 months, whereas 20 months for ALK(-) patients. The prognosis of ALK(+) group was better than that of ALK(-) group, survival curves of these two groups showed statistically significant (P < 0.05). CD99 was positive in 18 cases (72.0%) while negative in 7 cases (28.0%) of the latter 25 ALCL, ALK was positive in 19 cases (76.0%) while negative in 6 cases (24.0%); Of 19 ALK(+) ALCL, 16 (84.2%) cases co-expressed CD99-ALK; and in 6 ALK(-) ALCL, 2(33.3%) were CD99-ALK double negative, the expression of CD99 protein strongly correlated with that of ALK protein (P < 0.05). ALK and CD99 protein expressed in Karpas 299 cells with diffuse distribution.</p><p><b>CONCLUSIONS</b>CD99 highly expressed in ALCL, and showed high rate of co-expression with ALK. CD99 protein expression could be considered as a helpful diagnostic and prognostic factor of ALCL, especially for ALK(+) ALCL.</p>