Detection of Cup-like Blasts in Acute Myeloid Leukaemia

A 59-year-old female, presented with generalised weakness for several months. Her complete blood cell count revealed mild anaemia moderate thrombocytopenia with hyperleukocytosis. Differential leucocyte count revealed large number of blast cells (88%), with most of the blast cells having cup-like invaginations of nuclear membrane (giving it a fish-mouth-like nuclear appearance). Using a strict criteria of ≥10% blasts with nuclear invaginations and occupying ≥25% of nuclear area, most of immature cells were cuplike blasts. The blast cells had fine chromatin, high nuclear cytoplasmic ratio and 1 to 2 nucleoli. Cytoplasm of blast cells did not contain granules or Auer rods. Morphologically, the blast cells were suggestive of Acute Myeloid Leukaemia (AML) and the M1 subtype (FAB classification). Flow cytometric examination revealed moderate positivity for CD33 and mild positivity for CD11c, CD117 and CD45 antigens. Moderate expression of CD33 suggested aberrant expression on myeloid cells and Nucleophosmin (NPM 1) mutation.