Prognostic importance of Sudan Black positivity: a study of bone marrow slides from 1,386 patients with de novo acute myeloid leukaemia.

Analysis of bone marrow slides from 1,386 patients entered into the Medical Research Council's 8th and 9th trials in Acute Myeloid Leukaemia confirmed that features associated with differentiation in blast cells, in particular increasing Sudan Black (SB) positivity, were the most important morphological features for predicting remission achievement (P = 0.002) and hence survival (P less than 0.0001). SB positivity was also weakly predictive of remission duration (P = 0.05). A low complement of maturing granulocytes was associated with early induction death and a high percentage of blasts with shorter remissions. The few patients with acute promyelocytic leukaemia (FAB M3) had a high haemorrhagic death rate during induction and a low relapse rate. Apart from this, lineage involvement was not predictive of outcome. Multiple lineage leukaemias, in particular those with megakaryocytic and/or erythroid involvement, which had been reported previously to have a poor prognosis, did not have any worse remission rates in this series. When more than one cell line was involved, no combination with particularly good or poor prognosis could be identified. Multivariate analysis suggested that percentage SB positivity was adequate on its own to divide granulocytic leukaemias into poorly differentiated (less than 50% SB +ve) and well-differentiated groups (50% or more SB +ve) without the need for further measurements. This simple and reproducible test was strongly predictive of resistant disease but not of induction deaths. It was of considerably greater prognostic value--and was less open to inter-observer disagreement--than the FAB criteria which are usually used to classify granulocytic lineage leukaemias into the M1 and M2 subgroups. It is proposed that greater than or equal to 50% of blasts with SB positivity should replace blasts greater than 10% of maturing myeloid cells for this sub-categorization between M1 and M2.