If a patient's bone marrow shows 70% blasts that are negative for Sudan Black B, what is the likely diagnosis?

When a patient's bone marrow shows a significant percentage of blasts—specifically 70%—this indicates a high level of immature cells, which is typically associated with acute leukemias. In this scenario, the blasts being negative for Sudan Black B is a key detail in the diagnosis process.

Sudan Black B is a stain used to differentiate between types of leukemic blasts. It specifically stains lipids present in myeloid cells. Therefore, if the blasts are negative for this stain, it suggests that they are not of myeloid origin. This points away from diagnoses such as acute myeloid leukemia and acute promyelocytic leukemia, which would show positivity for Sudan Black B due to their myeloid lineage.

Given the negativity for Sudan Black B and the high percentage of blasts, the findings are consistent with acute lymphoblastic leukemia (ALL). This type of leukemia is characterized by the proliferation of lymphoid blasts, which do not contain the lipid components that would cause them to stain positively with Sudan Black B. Thus, the diagnosis in this case is acute lymphocytic leukemia.