Primary myelosarcomas are associated with a high rate of relapse: report on 34 children from the acute myeloid leukaemia–Berlin–Frankfurt–Münster studies

Primary myelosarcomas are rare manifestations of acute myeloid leukaemia (AML) that precede bone marrow involvement. Out of 744 children observed during the AML–Berlin–Frankfurt–Münster (BFM) studies 87 and 93, 34 children presented with extramedullar myelosarcomas and no blasts (n = 21; 2·8%), or a low blast count (n = 13; 1·7%) in the bone marrow. Owing to the initially mild and variable symptoms, in some children (n = 12) diagnostic procedures were delayed and treatment intensity was reduced. At 0·65 ± 0·13, the cumulative incidence of relapse was significantly higher than in other AML patients (0·28 ± 0·02). The 5‐year event‐free survival was 0·19 ± 0·08 (compared with 0·48 ± 0·02 in AML‐BFM studies 87/93; P(log rank)