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BACKGROUND The clinicopathologic and molecular features of the newly characterized Ki-1 lymphoma, although well studied in Western countries, are less well described in Asia. METHODS Pathology material of lymphoma cases, consecutively diagnosed at our institution between 1986 and 1994, was reviewed. The cases fulfilling the diagnostic criteria of Ki-1 lymphoma were selected, and their clinicopathologic features were studied. Immunohistochemistry and cytogenetic studies of the lymphoma tissues, and molecular analysis for nucleophosmin (NPM) gene translocation were performed. RESULTS A total of 13 cases (2.3%) of Ki-1 large cell lymphoma were identified from a total of 572 cases of non-Hodgkin's lymphoma diagnosed during this period of time. There were 10 men and 3 women with a median age of 43 years (range, 18 to 61 years). The initial presenting sites included the skin alone in five cases, lymph node alone in one case, both skin and lymph node in five cases, and the stomach in one case. All cases had large cell morphology, with the majority of the neoplastic cells expressing Ki-1 antigen (CD30). Except for the case with gastric involvement, all other cases were T-cell lymphomas. One of seven cases examined had chromosomal abnormality of t (2;5). Rearrangement of the NPM gene at chromosome 5 was detected by Southern blot analysis in three of nine cases. Two of seven cases tested by reverse-transcriptase polymerase chain reaction showed fusion of the NPM gene and anaplastic lymphoma kinase gene. Seven (78%) of 9 patients who had received systemic chemotherapy with a standard cyclophosphamide, doxorubicin, vincristine, and prednisolone regimen obtained a complete remission (CR). The median duration of remission was 33 months. Three (60%) of 5 patients, of whom 4 recurred from previous intensive chemotherapy, achieved a prolonged CR with treatment with 13-cis retinoic acid (RA). The median survival of the whole group has not yet been reached at a median follow-up of 40 months. CONCLUSIONS The clinicopathologic and molecular features of Ki-1 lymphoma of Chinese patients are comparable to those reported from Western countries. 13-cis RA appears to be an effective treatment of Ki-1 lymphoma. Cancer 1996;78:1805-12.