Clinical characteristics of pediatric patients with myeloid sarcoma without bone marrow involvement in Japan.

Myeloid sarcoma (MS) is a rare neoplastic condition that is often described in association with acute myeloid leukemia (AML). MS in childhood has received little attention, particularly in Japan. We carried out a nationwide retrospective analysis of Japanese children diagnosed with MS without bone marrow involvement. Inclusion criteria were diagnosis of MS at younger than 20 years of age between January 1, 2000 and December 31, 2013. There was a predominance of males (8:2), and the median age at MS diagnosis was 4 years. Sites of involvement varied and included skin (n = 3), head and/or neck (n = 2), and multiple sites (n = 2). Karyotypes were evaluated in seven patients, with one individual carrying t(8;21) and t(9;11). Four patients developed bone marrow involvement 2-55 months after diagnosis of MS. All patients received chemotherapy for de novo AML and two individuals received HSCT in first remission. Seven of ten patients survived for 50-152 months (median, 93 months) without disease after initial chemotherapy. This retrospective study confirmed that pediatric MS without bone marrow involvement in Japan is a very rare disease. MS patients responded favorably to therapies for de novo AML, and HSCT in first remission was not indicated for all patients.