ymphoblastic leukemia (ALL) of B-cell lineage can be classified using the French- American-British (FAB) classification as L1, L2 and L3 type. L1 and L2 ALLs express terminal deoxynucleotidyl transferase (TdT) and are surface immunoglobulin (sIg)-negative. SIg expression in adults with L1 or L2 ALL is extremely rare. We report a case of L1 ALL with positive sIg. A 39-year-old woman had suffered from fever and abdominal pain for 15 days. Her initial complete blood cell counts were WBC 1.3×10⁹/ℓ, hemoglobin 8.8g/㎗ and platelet 59.0×10⁹/ℓ. Blast cells on blood were counted up to 24% and showed typical FAB L1 morphology on bone marrow. Immunophenotyping was performed and showed expression of CD5, CD19, CD20, HLA-DR, TdT and sIgλ. Karyotype was 46,XX,der(8;9)(q10;q10),＋der(8;9) (q10;q10),t(9;22)(q34;q11.2)[3]/47, idem,＋der(22)t(9;22)[5]/46,XX[12]. The case was finally diagnosed as the sIg positive ALL, L1. Chemotherapy consisting of cytoxan, dau-norubicin, vincristine, L-asparaginase, prednisolone and intrathecal methotrexate was initiated. The patient had been in complete remission for 12 months. Twelve months later, blasts were detected in cerebrospinal fluid. The patient received intrathecal methotrexate and radiation therapy. Thereafter six months later, blasts were observed on peripheral blood. Bone marrow examination showed diffuse infiltration by blasts with L2 morphology and loss of previously positive sIg. At that time, she had given up the treatment. Although several cases of sIg positive B cell ALL, L1 or L2 have been reported, we could hardly find same case of ours in Korean.

Keywords: Acute lymphoblastic leukemia, L1, Immunophenotyping, Surface immunoglubulin, Terminal deoxynucleotidyl transferase