Acquired Trisomy 12 and Absent Y Chromosome in a Patient with Acute Undifferentiated Leukaemia

A 60‐year‐old man developed pancytopenia and then acute leukaemia. The neoplastic cells in marrow were undifferentiated by electron microscopy and by immunological and cyto‐chemical markers. The only other cells present in marrow were lymphocytes, plasma cells, macrophages and non‐haematopoietic elements. Prior to chemotherapy, cytogenetic analysis of marrow cells showed two karyotypically distinct cell populations, one with 45,X,‐Y and the other with a 46,X,‐Y, + 12 karyotype. All marrow cells stimulated by protein‐A from staphylococcus aureus were 46,X,‐Y, + 12. Phytohaemagglutinin‐stimulated cells were normal, 46,XY. These findings suggest strongly that most of the undifferentiated leukaemic cells were missing the Y chromosome. A subpopulation of these leukaemic cells also had trisomy 12. These observations and previously published findings suggest that trisomy 12 occurs non‐randomly in haematological disorders, and in particular, may be associated with B‐lymphoid malignancy.